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Kolloquien und Seminare (2011-2015)


2011 · 2012 · 2013 · 2014 · 2015


DateTimeTalk internal - external
2015 Dec 17 14:30

Gal Matijevic


RAVE Metal-poor Stars and Kepler Multiply Eclipsing System - Modeling the Noise

RAVE spectroscopic survey has enabled us to serendipitously discover many very metal-poor stars. Their signature spectra having only a few shallow spectral lines are easy to recognize. However, precisely measuring their metallicities has proven to be a difficult task. Firstly, their spectra have very weak lines which means their equivalent widths are harder to measure correctly. Secondly, the noise present in the spectra is correlated to an extent that cannot simply be neglected. We will review an approach for modeling the noise in their spectra which in turn enables us to measure the unbiased metallicity estimates with a flexible calibration model based on Gaussian processes. Altogether, we found more than 1000 very metal poor stars ([Fe/H] < -2), about 70 percent of which were previously unconfirmed. As a bonus, we will quickly go over a very different topic of modeling a quintuple eclipsing stellar system but using a very similar noise model. The mass and radii estimates of the two M-type components in this system are among the most precise ever obtained.

2015 Dec 15 11:00

Special Seminar: Sergey Pilipenko

(P.N. Lebedev Physical Institute, Moscow)

Ginnungagap -- a massively parallel zoomed cosmological initial conditions generator

Ginnungagap is a code for generating cosmological initial conditions. It is aimed at high scalability and ease of use. The main code will generate the velocity field at the requested starting redshift, which is then used by extra tools to generate a particle representation. In this talk the features of the code will be presented with the emphasis on the methods of rescaling of the initial conditions to higher resolution while preserving the same large scale structure.

2015 Dec 10 14:30

Smitha Narayanamurthy


Deciphering the polarized spectrum of the Sun with atomic physics

The Sun with its low density atmosphere provides us with a unique astrophysical laboratory to test some of the interesting and rare atomic effects. These effects are often not observed in the terrestrial laboratories. One such is the quantum mechanical interference between the atomic states. This talk discusses the signatures of these interferences in the polarized spectrum of the Sun and our efforts in modeling them. A detailed comparison between the observed and synthesized profiles will be presented, with a few examples. Finally, the diagnostic potential of such atomic lines for the measurement of chromospheric magnetic fields will be discussed.

2015 Dec 03 14:30

John Peacock


Gravitational lensing of the Cosmic Microwave Background: flux conservation and growth of inhomogeneities

Gravitational lensing is a rich source of cosmological information: it probes both the amplitude and evolution of metric fluctuations, plus the distance-redshift relation via the geometry of the distortion of background images. But in 2014, Clarkson et al. suggested that lensing had an average non-Newtonian "back-reaction" effect, which altered the effective distance to the CMB last-scattering surface, potentially by several percent - enough to cause substantial change in the cosmological parameters we infer. The first part of this talk discusses this issue from the point of view of flux conservation theorems due to Weinberg and to Kibble & Lieu, and a possible loophole in these theorems is identified. This loophole relates to the area of constant-redshift surfaces, and the solution to this puzzle is critical in order to decide whether the Clarkson et al. claims should be taken seriously. The second part of the talk presents some new results on cross-correlation between galaxy surveys (based on WISE & SuperCOSMOS) and CMB lensing data. These yield interesting measurements of the evolution of cosmological perturbations at redshift z<0.35.

2015 Dec 02 11:00

Special Seminar: John Peacock


Vesto Slipher and the discovery of the expanding universe

We have known about the expanding universe for around a century, but the story of this discovery has been obscured by a number of myths. Chief among these has been the role attributed to Edwin Hubble, and far too little credit has been given to the true pioneers in this field. More than anyone, the figure of Vesto Slipher stands out. Working in isolation at the Lowell Observatory in Arizona, he was the first to prove the true nature of galaxies and demonstrate that they are in motion (including the motion of our own Milky Way). Slipher's first results were published in 1913, and this recent centenary gives good reason to highlight Slipher's achievements, and how they were used by the astronomers who came after him.

2015 Nov 27 11:00

Special Seminar: Ryan Leaman


Cooling and heating in the Milky Way's Goldilocks disk

I will discuss an effort to constrain the accretion history of the Milky Way (MW), by jointly examining the amount of disk heating (as traced by an increase in stellar velocity dispersion of the disk stars of different ages) experienced by the MW from infalling satellite galaxies, and by considering the populations of Globular Clusters that the accreted satellite galaxies might bring with them to the MW's stellar halo. Key to this exercise are new semi-analytic estimates for the energy injection of satellites an orbits of arbitrary circularity, and an empirical estimate for the velocity dispersion of the dynamically hot gas that stars in the MW disk might be born out of at high redshift. I will show that the observed Globular Cluster populations and MW disk structure, are consistent with the MW experiencing a merger history similar to those in cosmological simulations, including one or two 1:10 mass ratio accretion events - provided that the MW's gas disk was already dynamically hot at early times from internal processes (e.g., supernovae feedback and gravitational instabilities).

2015 Nov 26 14:30

Sarah Jane Schmidt


Hot Chromospheres and Flares on Cool and Ultracool Dwarfs

Cool (M) and ultracool (late-M and L) dwarfs include both the least massive stars and warmest brown dwarfs. While their photospheres are characterized by cool (or ultracool) temperatures, the presence of strong surface magnetic fields on many of these objects results in hot chromospheres. On these M and L dwarfs, hot chromospheres are traced by both Halpha emission (in quiescence) and dramatic multi-wavelength flare events. Using detections of Halpha in spectroscopic data primarily from the Sloan Digital Sky Survey, I will examine the changing relationship between activity and age over the M/L spectral sequence. The combination of the strength of these detections with one-dimensional chromosphere models reveals strong changes in the chromospheric heating over the same range of spectral types. I will also discuss the limited flare detections on ultracool dwarfs, placing them in the context of flare observations on cool (early- to mid-M) dwarfs. Flares may prove to be a powerful age indicator in future multi-epoch surveys.

2015 Nov 19


Who does what?

The seventh round of speakers:

Gernot Rosenkranz, Tanya Urrutia, Jakob Walcher,
Chia-Hsun (Albert) Chuang, Dario Fritzewski, Philipp Gast,
Clemens Konrad, Rikke Lund Saust, Sarah Jane Schmidt,
Sabine Thater, Ugur Ural, Michael Weber,
Jörg Weingrill, Lutz Wisotzki, Kris Youakim,
Udo Ziegler

You can download the talks here (pdf, 28 MB).

2015 Nov 05 14:30

Joachim Wambsganss


Searching for Extrasolar Planets with Gravitational Microlensing: Challenges and Exciting Results

Gravitational microlensing is a very powerful method for the detection of extrasolar planets. In particular its sensitivity to low mass exoplanets and its potential for global statistical analyses are highly relevant. In the talk the basics of this technique and its current mode of operation will be explained as well as its advantages and disadvantages compared to other planet-search methods. About three dozen planets have been discovered so far by microlensing surveys. A couple of microlensing exoplanets will be reviewed in detail. A recent statistical investigation on the Galactic abundance of (bound and possibly unbound) exoplanets will be presented and discussed, with particular emphasis on the result that “Planets are the rule, not the exception”: Abundances analyses show that on average every Milky Way star has at least one planet! In a brief outlook, the immense potential of gravitational microlensing for detections of Earth- and Mars-mass planets, of exomoons and of free-floating planets will be highlighted.

2015 Oct 30 14:00

Fifth Potsdam - Berlin Astronomical Colloquium

(at TU Berlin)

You can download the program here (pdf, 1 MB)

2015 Oct 15 14:30

Arianna DiCinto

(Dark, Copenhagen)

The cusp-core crisis: the mass dependent density profiles for DM haloes and its applications

We have derived a mass dependent (DC14) density profile based on the impact of baryonic physics on dark matter haloes that host observed galaxies, using a suite of hydrodynamically simulated galaxies. The main feature is a clear dependence of the inner slope of the dark matter density profile on the ratio between stellar-to-halo mass, with the cored most galaxies expected at a mass M*=108.5 Msun. This prediction for cusps vs cores can be applied to the Local Group, allowing to reconcile abundance matching predictions, “too big to fail” problem and star formation efficiency of such galaxies. Application of the DC14 profile on observable properties of galaxy populations, such as velocity function, mass discrepancy acceleration relation and rotation curves fitting, will be shown as well proving the validity of this modelization of dark matter haloes.

2015 Oct 13

Special Seminar: Lutz Wisotzki


Decision processes at the DFG

For the last 4 years I served on the Astronomy and Astrophysics Board of Reviewers ("Fachkollegium") at the German Science Foundation (Deutsche Forschungsgemeinschaft; DFG). In this seminar I wish to share some of my experiences and insights. I will give an overview about the multi-step process of decision making at DFG, and highlight a few aspects that are maybe not always known or appreciated. And I will of course try to answer questions. (But I will *not* lecture about how to write a good DFG proposal - that would be a big topic on its own.)

You can download the talks here (pdf, 0.5 MB).

2015 Oct 08

Claudia Stolle


Variation and sources of the geomagnetic field

The Earth's magnetic field varies on different time and spatial scale lengths. Its dipole moment is presently decreasing on time scales of decades. During geomagnetic weather the magnetic field changes rapidly between seconds and days. The observation and analysis of the Earth’s magnetic field receives increasing interest for the modern society that becomes vulnerable to technology. On the other hand, modern observations and modelling of the geomagnetic field allows us to better understand underlying processes that infer geomagnetic field variations. This presentation will provide an overview on the activity in geomagnetic field research at GFZ.

2015 Oct 01

Claude Mack


Do some host stars ingest their rocky planets?

Stars with close-in giant planets may be more likely to ingest their inner rocky planets. Numerical simulations of giant planet migration suggest that migrating giant planets may disrupt the orbits of interior rocky planets by either ejecting them from the system, scattering them to the outer regions of the system, or by scattering them in towards the host star.

My talk will present the current progress of an ongoing project that seeks to detect a potential chemical signature of rocky planet ingestion by studying the detailed chemical abundances of host stars with wide binary companions. A wide binary companion allows us to compare the chemical abundances of the host star with those of a star that most likely formed at the same time and from the same material. Furthermore, we have performed a simple back-of-the-envelope calculation for how the ingestion of Earth-like rocky planets would affect the photospheric abundances of a Sun-like star. Therefore, we can compare any difference we detect between the chemical abundances of the host star and its companion with the differences predicted by our model, and thereby determine how likely it is that the host star has ingested a significant amount of rocky planetary material.

2015 Sep 24

Darren Croton


How to model the Universe in N easy steps (N>>1)

Much progress has been made in recent years in our understanding of the co-evolution of galaxies and supermassive black holes, and their connection to the underlying large-scale dark matter structure. In this talk I will discuss simulation and modelling techniques that bridge theories of galaxy and black hole formation with the properties of observed galaxy populations. In addition, I will discuss a number of open questions important for extra-galactic astronomy and cosmology, and explain how future large-scale surveys and galaxy formation models may jointly address them.

2015 Sep 15

Federico Sembolini

(UAM Madrid)

Exploring the properties of galaxy clusters with hydrodynamical simulations: the MUSIC dataset

I will introduce the MUSIC dataset (Marenostrum-­‐MUltiDark Simultations of galaxy Clusters) -­ presently the largest sample of hydrodynamically simulated galaxy clusters. The MUSIC dataset comprehends more than 700 clusters and 2000 groups simulated in three differentflavours (non-­‐radiative physics, radiative physics including cooling and star formation with and without AGN feedback). The analysis of the baryon content (gas and stars) of the most massive clusters of the MUSIC dataset is compared with the most recent observational estimates of the gas fraction in galaxy clusters, also estimating the impact of the different physics used in the simulation on the results.

I will also present a detailed analysis of the scaling relations of the thermal Sunyaev-­Zel'dovich effect derived from MUSIC clusters. The integrated SZ brightness, Y, is one of the best observational proxies used to infer the total cluster mass.

MUSIC clusters have also been used to assess the reliability of cosmological hydrodynamical simulations of clusters. A comparison of 12 different codes has been performed, including particle based, moving and fixed mesh codes as well as both Eulerian and Lagrangian fluid schemes. We show that methods with modern SPH schemes can recover gas entropy profiles that are essentially indistinguishable from those obtained by grid based methods.

2015 Sep 08

Jean Michel Gomes

(Instituto de Astrofísica e Ciências do Espaço, CAUP, Porto, Portugal)

2D Spectral synthesis studies of early-type galaxies from CALIFA survey

The lambda-by-lambda spectral fitting approach as a mean to estimate physical properties of galaxies, such as the star-formation history, total stellar mass, extinction and kinematics has proved to be one of the most powerful methods available in extragalactic astronomy. A prolific decade with large and high-quality fiber-fed data bases of galactic spectra (e.g, SDSS, 6dF and GAMA surveys), and the combination of a wide set of stellar population libraries, computed from evolutionary synthesis models, together with much refined population synthesis codes has permitted to significantly improve our understanding on the mass assembly and chemical enrichment history of galaxies.

However, our understanding on galaxy formation and evolution essentially relies on single-fiber and long-slit spectroscopy covering only a minor fraction of a galaxy. Integral Field Spectroscopy opens a new window for studying age, metallicity and kinematics of stellar populations over the full spatial extent of galaxies.

I will provide an overview of our ongoing studies of early-type galaxies (ETGs) from CALIFA with our spectral analysis pipeline Porto3D. The main goal of our studies is to investigate the 2D physical characteristics and excitation mechanisms of the warm interstellar medium in ETGs. In Gomes et al. 2015, we study the contribution of photoionization by the post-AGB stellar component to the gas excitation on galactic scales as well as diagnostic emission-line ratios and gas/stellar kinematics.

Among other findings, we identified a small fraction (~10%) of ETGs hosting star-forming spiral-arm like features in their periphery (R >~ effective radius). We show that these features are localized signatures of a still ongoing inside-out galaxy growth process and point out the importance for advancing our understanding of spiral structure within triaxial stellar systems. Additionally, we study both empirically and theoretically how aperture effects might impact the spectroscopic classifications of such ETGs and their morphological analogs.

2015 Sep 03

Facundo Gomez


A deeper look at the impact of minor mergers on the observable properties of the Milky Way

During this talk I will present an overview of our recent work which aims to characterize the impact of host-satellite interactions on the observable properties of our Galaxy. Using fully cosmological simulations of the formation of the Milky Way (MW), I will start by showing how a low-mass low-velocity fly-by encounter with a pericentric distance as large as 80 kpc can excite well-defined vertical patterns on a pre-existing galactic disk. I will discuss the mechanism behind these perturbations and show how such an interaction could be enough to induce the formation of observed features such as the Monoceros Ring. Motivated by recent studies suggesting that the Large Magellanic Cloud (LMC) could be significantly more massive than previously thought, I will then explore whether the approximation of an inertial Galactocentric reference frame is still valid. I will show that previous estimates of the LMC's orbital period and apocentric distance, derived assuming a fixed MW, are shortened if the MW is allowed to freely move in response to the gravitational pull of the LMC. Due to this interaction, the MW center of density can be strongly displaced in phase-space in a very short period of time. Such previously ignored interaction is likely to significantly affect both the orbit and phase space distribution of tidal debris from MW satellites such as the Sagittarius dwarf galaxy (Sgr). In addition, it can also affect previous estimates of the (timing) mass of the Local Group.

2015 Aug 17

Special Seminar: Petri Käpylä

Modeling spot forming dynamos - current perspectives and future challenges

Self-consistent global and semi-global simulations of convection-driven dynamos in spherical coordinates are now used routinely to study stellar magnetism. Phenomena such as equatorward migration of activity belts and longitudinal dynamo waves have been obtained from such simulations and can be associated with magnetism in the Sun and more rapidly rotating rotating late-type stars, respectively. Furthermore, recent high-resolutio simulations are beginning to resolve the small-scale granulation near the surface and capture the near-surface shear layer observed in the Sun. The magnetic fields in the global simulations are typically diffuse and the resolution is in general too low for spot formation. Recent local models, encompassing only a small fraction of the convection zone have, however, shown spontaneous formation of spot-like features.

Combining the global dynamo action and spot-formation into a single model that can be used to compare to real stars is a grand challenge that requires not only substantially higher resolution than what is feasible today but als improvements in terms of subgrid-scale physics and advanced computational methods that can cope with exascale datasets.

In this talk the current status of global modeling of stellar magnetism and our understanding of spot-formatio processes is reviewed and the requirements for combining the two into a single model are outlined.

2015 Aug 13

Marcel Pawlowski

(Case Western Reserve University, Cleveland USA)

Co-orbiting satellite planes and dwarf galaxy structures in the Local Group

Comparisons of observed satellite galaxies with ΛCDM simulations have revealed numerous 'small-scale' problems. While the missing-satellites, the core-cusp and potentially even the too-big-to-fail problems might be solved by invoking baryonic processes, the problem I will present still lacks an viable solution in the ΛCDM framework. The satellites of the Milky Way and of the Andromeda galaxy preferentially co-orbit within narrow planes, and there is increasing evidence that satellite planes are also present around more distant hosts. I find that similarly anisotropic phase-space distributions of sub-halos are extremely rare in cosmological simulations. This makes the satellite planes one of the most-serious small-scale problem for ΛCDM, because the distribution of sub-halos on scales of hundreds of kpc is dominated by gravitational effects and not strongly affected by baryonic physics. While scenarios explaining the coherence of satellite positions and orbits exist, none of them are without problems, and some require radical adjustments to the ΛCDM model. I will discuss the highly controversial current situation and address why some recent studies claim consistency between ΛCDM and observed satellite planes while others find the opposite. Finally, I will argue that to find a solution, we must consider the overall phase-space distribution of dwarf galaxies in the Local Group, including the mutual relation between the MW and M31 satellite planes, the highly symmetric non-satellite dwarf galaxy planes in the Local Group and other aligned features such as the Magellanic Stream.

2015 Jul 14

Special Seminar: Rolf Kuiper

The Formation and Feedback of the Most Massive Stars

Importance of massive stars: Stars with more than 100 times the mass of our sun are observed in the present-day universe. These \cf2 massive stars are of great importance for a wide range of astrophysical problems. In spite of the fact that they are both rare and short-living, they represent the major source of radiation energy in their stellar clusters. Therefore, they act as valuable tracers of star formation in distant galaxies. Additionally, the radiation emitted during a massive star\'92s lifetime influences the surroundings through various interactions such as heating and ionization of gas, evaporation of dust, and radiative forces leading to powerful stellar winds and outflows. Finally, when a massive star dies, it enriches its neighborhood with heavy elements. In this sense, massive stars are the main drivers of the morphological, dynamical, and chemical evolution of their complex environments.

Observational difficulties of massive star formation: However, knowledge about their formation is rather poor compared to the case of low-mass star formation. Observationally, this is mostly due to their larger average distances to us and the fact that they are deeply embedded in dense, opaque cores of gas and dust especially during their early evolutionary phases. Also, their short lifetime, rareness, and complex environment pose difficulties for detailed observations. Nevertheless, current observational results support the assumption that the basic concepts of star formation, including the collapse of an unstable gas and dust core, the formation of both bipolar outflows and jets, as well as accretion disks, are possibly valid throughout the whole range of stellar masses.

Theoretical problems of massive star formation: From the theoretical point of view, assuming that the formation of high-mass stars is basically a scaled-up version of low-mass star formation, implies its own challenges: Their rapid evolution inside the collapsing core leads to the interaction of the in-falling accreting flow of gas and dust with the emitted radiation from the newborn star. The radiative force of the emitted photons onto the stellar environment thereby quickly exceeds the gravitational attraction of the nearby dust grains by the star. How is such a star able to sustain accretion despite its superior radiative force to allow the formation of the most massive stars observed?

Our methods: In this talk I present the results of several series of self-gravitating radiation-hydrodynamics simulations of core collapse towards high-mass star formation. To be able to study in especially the radiation pressure problem in high detail, we have developed a specially adapted hybrid radiation transport scheme for problems of dominating radiative point sources.

Our findings: The classical accretion disk scenario of star formation self-consistently allows to circumvent the radiation pressure problem: Due to angular momentum conservation, the forming high-mass protostar is surrounded by an high-mass accretion disk. The irradiated and heated inner rim of such an accretion disk re-emits the radiative flux preferentially perpendicular to the disk's midplane (due to the fact that the optical depth in this direction is much smaller than in any other). This anisotropy of the thermal radiation field allows the accretion to continue in the shadow behind the inner disk rim, while the strong radiative force in the direction perpendicular to the disk yields the launch of wide-angle radiation-pressure-dominated outflows. By this process, roughly half of the initial core mass is blown away from the evolving system. The angular momentum transport - required for ongoing accretion through the circumstellar disk - is provided self-consistently by the strong self-gravity of the disk, which yields the formation of spiral arms in the disk.

Summary: I will demonstrate a straight-forward and self-consistent mechanism, which allows the formation of the most massive stars known in the present-day universe despite of their strong radiative feedback. The basic theory of star formation herein is just a scaled-up version of low-mass star formation.

Outlook: If time permits, I will further elaborate on our recent results on feedback of protostellar outflows from massive stars as well as preliminary results on their ionization feedback.

2015 Jul 09


Who does what?

The sixth round of speakers:

Orkun Özdarcan, Janine Fohlmeister, Steffen Frey,
Rohan Louis, Daniel Sablowski, Sergej Schmalz,
Olivier Schnurr, Else Starkenburg, David Streich,
Iris Traulsen, Marica Valentini, Senthamizh Pavai Valliappan,
Meetu Verma, Christian Vocks, Alexander Warmuth,
Peter Weilbacher, Matthias Winker, Roland Winkler,
Jennifer Wojno, Hauke Wörpel, Marina Zajnulina,
Mirko Krumpe

You can download the talks here (pdf, 16 MB).

2015 Jul 06 14:00 Special Seminar: Tonatiuh Matos

(Cinvestav, Mexico-City)

Scalar Fields as the Dark Matter of the Universe

The Scalar Fields as Dark Matter behaves exactly in the same way as Cold Dark Matter (CDM) at cosmological scales. Nevertheless, at galactic scales this model predicts flat central density dark matter profiles and a natural cut off of the mass power spectrum, given rise to less formation of substructure as CDM. In this talk we review this properties, deduce some of them in a very simple way and show numerical simulations of galaxies, where the gas form spiral arms and bars as the real galaxies. We conclude that this model fits well the observations at all scales in a simpler way as the CDM paradigm does.

2015 Jul 01

Special Seminar: Mia Sauda Bovill

(FONDECYT IA-PUC, Chile *** moving to STScI in October)

The Evolution of the Dwarf Satellites of Centaurus A.

I will present work using the interface of simulations and observations to undertake the first detailed study of the complete dwarf satellite population of a galactic system beyond the Local Group. In this talk, I will present initial results from a set of high resolution cosmological N-body simulations of Centaurus A, a 10^13 solar mass halo approximately 3 Mpc from the Local Group. When coupled with our Survey of Centaurus A's Baryonic Structure (SCABS), this work will be a powerful addition to near field cosmology. In addition, I will discuss a possible formation scenario for the observed high M/L Centaurus A globular clusters (Taylor et al, 2015) within a cosmological context.

2015 Jun 30

Special Seminar: Brent Groves

(ANU, Canberra/Australia)

Tracing Gas in Galaxies Near and Far

The gas in galaxies is the fundamental fuel for star formation, and its presence is the prime driver for galaxy growth. However measuring gas systematically in galaxies is not a simple process: neutral hydrogen is only measured in absorption beyond the local Universe and cold molecular hydrogen cannot be traced directly, and so is determined through CO emission, an optically-thick tracer. I will discuss here how we can determine the total gas mass in both nearby and distant galaxies using our knowledge of HI, CO, and dust, and touch upon our understanding and recent measurements on how this drives the growth of galaxies over cosmic time.

2015 Jun 26

Special Seminar: A. C. Lanzafame

(Universita' di Catania)

Rotational evolution of slow-rotators sequence stars

The mass-age-rotation relationship observed in open clusters shows the progressive development of a slow-rotators sequence at masses lower than 1.2 Msun. After 0.6 Gyr, almost all stars have settled on this sequence. The observed clustering on this sequence suggests that it corresponds to some equilibrium or asymptotic condition that still lacks a complete theoretical interpretation, crucial to our understanding of the stellar angular momentum evolution. We couple a rotational evolution model that takes into account internal differential rotation with classical and new proposals for the wind braking law, and fit models to the data using a Monte Carlo Markov Chain method tailored to the case at hand. We explore the extent to which these models are able to reproduce the mass and time dependence of the stellar rotational evolution on the slow-rotators sequence.

The description of the early evolution (0.1 to 0.6 Gyr) of the slow-rotators sequence requires taking into account the transfer of angular momentum from the radiative core to the convective envelope of the stars. We find that, in the mass range (0.85, 1.10) Msun, the core-envelope coupling time-scale for stars in the slow-rotators sequence scales with mass as a power law. After most of the angular momentum stored in the radiative core is transferred to the convective envelope, the rotational period evolution on the slow-rotators sequence follows quite closely the Skumanich law (P proportional to t).

The observed evolution between 0.1 and 2.5 Gyr is best reproduced by assuming that the wind angular momentum loss is proportional to the convective turnover time-scale, the stellar moment of inertia, and to the cube of the envelope angular velocity. We therefore confirm that the convective turnover time-scale is a key parameter in the wind braking law.

2015 Jun 25

Christian Fendt


How to make astrophysical jets?

I will present MHD simulations investigating the launching of astrophysical ets. Our simulations treat the time-dependent evolution of the accretion-ejection structure and the subsequent collimation of the disk wind into a high-velocity jet. Our setup considers various models for a physical (turbulent) magnetic diffusivity that is essential for the mass loading of the outflow. We find relatively high mass fluxes in the outflow, about 20-40% of the accretion rate.

We also consider simulations treating jet launching in a truly bipolar setup, thereby investigating the origin of an intrinsic jet-counter jet asymmetry. Most recent simulations include a mean-field accretion disk dynamo and the launching of outflows by a self-generated disk magnetic field.

2015 Jun 17

innoFSPEC colloquium

Due to their outstanding ability to manipulate the light, integrated optics and optical fibre based components will continue to have a central role in future design of ground- and space-based instruments for astronomy. Research in the emerging field of Astrophotonics – in which innoFSPEC is one of the world pioneers – promises to offer solutions to many practical problems, in particular to address the huge challenges in connection with building large diameter telescopes. Nowadays, Astrophotonic developments include - amongst other - fibre based optical frequency combs for calibration in spectroscopy, fibre Bragg gratings used to filter out atmospheric emission lines, and integrated optic devices. The Colloquium will give a short overview of the above aspects by means of three short thematic seminars (15 min. each).

2015 Jun 09 14:00

Special Seminar: Ana Gonzalez-Galan

(University of Potsdam)

Multi-wavelength study of SXP 1062: A young and slowly rotating X-ray pulsar of the SMC

X-ray binaries are point-like X-ray sources which consist of a compact object (neutron star or stellar black hole) orbiting a "normal" star from which there is an accretion of material. This material is accelerated to extremely high velocities due to the strong gravitational field of the compact object, and rapidly decelerated when it reaches the surface of this compact object. The free-fall kinetic energy resulting from this process is radiated away giving as a result the observed X-rays. X-ray pulsars are X-ray binaries in which the compact object is a rotating neutron star. SXP 1062 is a long period X-ray pulsar in the Small Magellanic Cloud associated with the supernova remnant MCSNR J0127-7332. This association makes it possible to estimate the age of the neutron star with a value of ~2x10^4 years. This young age, the long rotational period of the X-ray pulsar (>1000s), and the fact that it spins down during the accretor phase, present a challenge for the understanding of the formation and evolution of such systems.

2015 Jun 03 14:00

Special Seminar: Brent Tully

(IfA, Hawaii)

3. Wempe Lecture, "Galaxy Groups"

2015 May 29

Georges Meynet

(Geneva Observatory, Switzerland)

The first generations of stars in the Universe

After a recall of the main observations of the surface abundances of the most iron-poor stars in the halo, we shall discuss what these observations tell us about the nucleosynthesis occurring in the first stellar generations in the Universe. We shall show that, independently of the stellar models, two points can be deduced just from considerations based on the nuclear reactions active in the H- and He-burning regions: 1.- the need for some partial mixing between the H- and the He-burning zones; 2.- Most of the first stars must have chemically enriched their environment by the loss of their H-rich envelope, keeping the contributions from the regions inside the He-burning zone at a modest level. We shall then discuss what could be the physical causes responsible for the mixing implied by point 1, and for the loss of only the outer layers implied by point 2. Among the physical mechanisms, axial rotation does appear as very promiseful. This would imply relatively fast initial rotations for the first stars. Implications of this fast rotation on other questions as the origin of the anti-correlation in the globular clusters, the expected frequency of long Soft Gamma Ray bursts in the early Universe, or the contribution of stars in ionizing photons at early cosmic epochs will be briefly mentioned.

2015 May 28

Brent Tully

(IfA, Hawaii)

Large Scale structure velocity fields

Coherent flows are a fundamental property of the development of large scale structure. In a universe with matter density well below closure density, local velocity dispersions are small and motions are coherent. Structures on intermediate scales are strongly affected by large scale tides. Current observations of motions that deviate from the cosmic expansion are providing an increasingly nuanced picture of structure on a wide range of scales.

2015 May 27 14:00

Special Seminar: Brent Tully

(IfA, Hawaii)

2. Wempe Lecture, "The extra galactic distance scale"

2015 May 21 10:30

Donald Lynden-Bell

(Cambridge, IoA)

Magnetic Jets

The main thrust of this is to answer the question "Why are there Jets at all"? I shall then concentrate on the abstract problem of a massive thin differentially rotating accretion disk dragging around the feet of a magnetic field which is dominant in the surrounding magnetosphere. I give both some exact solutions for force-free fields and more general Energy Principles that give trial- function solutions. The primary results only require the knowledge that the magnetic field energy density is B^2/(8 pi) and that equilibrium fields take up minimum energy configurations subject to the boundary conditions.

2015 May 20

Special Seminar: Brent Tully

(IfA, Hawaii)

1. Wempe Lecture, "Topics Concerning Galaxy Groups"

2015 May 20

Special Seminar: Seshadri Nadathur

(University of Helsinki)

Understanding the nature of voids: simulations, the relation to theory, and use in cosmology

Cosmic voids are an exciting tool which can potentially be used to test a number of different cosmological models, including the growth of structure, dark energy and modified gravity. Yet voids are not well understood. I will discuss the general properties of voids in simulations show that they do not match the predictions of the standard theoretical model of voids based on the excursion set formalism. I will discuss the reasons for this discrepancy and argue that it points to the need for simulation-based calibration of void properties for comparison with observation. I identify some universal properties of voids which are independent of the bias and sampling density of the galaxies which are used to identify them, in particular the way in which they trace maxima of the gravitational potential field. This provides clues to the void environment and greatly aids the use of voids in cosmological studies.

2015 May 07

Gabriel Bihain


Mid-infrared search for substellar companions to Barnard's Star

Beyond Alpha Centauri, Barnard's Star is the second nearest star system to the Sun. Its relatively old age typical of solar neighborhood stars implies very low-mass brown dwarf companions and giant Jupiter-like planets would have reached temperatures below 500 K and emit most of their light in the mid-infrared. Direct imaging searches explore a range of physical separations complementary to that of radial velocity or transit methods, a range also where most giant planets are expected to form. Therefore, we obtained mid-infrared images in the 8.7 micron band (Si-2 filter) with 10.4 m GTC/CanariCam at two epochs and searched for low-mass companions at orbital separations of 1.8-25 astronomical units (au). Despite a spatial resolution of 0.5 au and a detection sensitivity of about 1.0 mJy, near the brown dwarf - planet mass boundary, no sources other than the star were found, indicating no brown dwarf companions. As a corollary and considering previous searches, giant planets in wide orbits may still be discovered by deeper searches.

2015 May 06

Special Seminar: Pier-Emmanuel Tremblay

(STScI Baltimore)

Evolution of White Dwarfs and Magnetic Fields

The vast majority of stars will become white dwarfs at the end of the stellar life cycle. These remnants are precise cosmic clocks owing to their well constrained cooling rates. By employing spectroscopically derived atmospheric parameters, white dwarfs constrain the stellar formation history in the early developing phases of the Milky Way, the initial mass function in the 1.5-8 solar mass range, and the mass loss during the post main-sequence evolution. White dwarfs also harbor evolved planetary systems. We have completed the first grid of 3D RHD model atmospheres for white dwarfs and have connected these surface calculations to structure models, creating a robust framework to study all stellar remnants without resorting to free parameters for the treatment of convection. The new generation of white dwarf models will strengthen the use of white dwarfs as cosmochronometers and maximize the science output from GAIA and 4MOST in the next decade. I will also discuss our new evolution sequences for magnetic white dwarfs using MHD simulations as outer boundary condition, providing new insights on the origin and photometric variation of these remnants.

2015 May 05

Special Seminar: Julius Koza

(Astronomical Institute of the Slovak Academy of Sciences, Tatranska Lomnica, Slovakia)

THEMIS spectropolarimetry of quiescent prominences

The talk reports on spectropolarimetric observations of quiescent prominences in the He I D3 line performed by the THEMIS telescope in the summer 2014. For selected samples, we show results of inversion of the data and measured Doppler velocities and discuss them comparing with the simultaneous GONG Halpha imagery. The talk also presents plans and outlooks for interpreting data by the HAZEL inversion code and integrating data into wider context of prominence research.

2015 May 04 11:00

Special Seminar: Peter Behroozi

(STScI Baltimore)

Exploiting The Connection Between Galaxies and Halos from z=0 to z=15

We present a robust, self-consistent, semi-empirical model which matches observed galaxy stellar masses and star formation rates over nearly all of observed cosmic history. Key results include constraints on star formation rates as a function of halo mass, average star formation histories for galaxies from z=0 to z=8, and the buildup of the intracluster light as a function of halo mass and time. We also examine the connections between halo growth and galaxy growth, and we find that the universe's star formation history since z~4 can be explained by a star formation efficiency which is strongly dependent on mass but only weakly dependent on time. We discuss how it is possible to physically extend the connection between galaxies and halos to very high redshifts, allowing predictions for what the James Webb Space Telescope will be able to see out to z=15.

2015 Apr 30 14:00


Who does what?

The fifth round of speakers:

Roelof de Jong, Christoph Kuckein, Andrea Kunder,
Claude Ernest Mack III, Isha Pahwa, Pouneh Saffari,
Christer Sandin, Allar Saviauk, Elmar Schmälzlin,
Ralf-Dieter Scholz, Axel Schwope, Jenny Sorce,
Federico Spada, Federico Stasyszyn, Matthias Steffen,
Matthias Steinmetz, Marvin Stolz, Jesper Storm,
Ole Streicher, Carsten Denker

You can download the talks here (pdf, 15 MB).

2015 Apr 16

Joe Silk

(IAP, JHU and Oxford)

The Challenge of Galaxy Formation

The origin of the galaxies represents an important focus of currentvcosmological research, both observational and theoretical. Itsvresolution involves a comprehensive understanding of star formation,vgalaxy dynamics, supermassive black holes, and the cosmology of thevvery early universe. It is a field that is largely driven by avphenomenology that depends on our accumulating data taken with the largest available telescopes. I will review our current understanding of galaxy formation and describe some of the challenges that lie ahead. Specific issues that I will address include the star formation rate in galaxies and the galaxy luminosity function, including the role of feedback.

2015 Mar 27 10:30

Kai Polsterer

(Heidelberg Institute for Theoretical Studies)

Machine Learning in Astronomy - small lessons learned from learning machines

The amount and size of astronomical data-sets was growing rapidly in the last decades. Now, with new technologies and dedicated survey telescopes, the databases are growing even faster. VO-standards provide an uniform access to this data. What is still required is a new way to analyze and tools to deal with these large data resources. E.g., common diagnostic diagrams have proven to be good tools to solve questions in the past, but they fail for millions of objects in high dimensional features spaces. By applying technologies from the field of computer sciences this data can be accessed more efficiently. Machine learning is a key tool to make use of the nowadays freely available datasets. This talk exemplarily presents what we learned when using machine learning algorithms on real astronomical data-set.

2015 Mar 19 14:00

Andreas Korn

(Uppsala University, Uppsala, Sweden)

M67: the birth cluster of the Sun?

I will discuss our on-going work to define the chemical profile of stars in the solar-age, solar-metallicity cluster Messier 67. The remarkable chemical similarity of the first confirmed solar twin in M 67 to the Sun (Önehag et al. 2011) made us tentatively suggest a solar origin as part of this rather unique cluster. But can the dissimilarity of the orbits, in particular the current high Galactic latitude of M 67, be reconciled with this hypothesis? And what about the idea that solar-like abundance profiles reveal the presence of terrestrial planets? I will argue that M 67 holds key observables for open questions related to planetary, stellar and Galactic astronomy.

2015 Mar 18 15:30

Special Seminar: Hitoshi Hanami

(Physics Section/Fac Humanities, Iwate University, Japan)

Unveiling Dusty Star Formation and AGN Activities in high-z LIRGs

A major issue in observational cosmology is to reconstruct the growth history of galaxies and Active Galactic Nuclei (AGNs), which can be traced with Luminous InfraRed Galaxies (LIRGs) detected by the infrared observing satellites as the ISO, Spitzer, AKARI, and Herschel. Their IR emissions are expected not only with Star Formation (SF) but also with AGN activities, which possibly regulate or quench the SF with their feedback mechanism in galaxy evolutions. We can classify LIRGs into starburst (sb-LIRGs), starburst-AGN (s/a-LIRGs), and AGN (agn-LIRGs) populations with the flux ratio of FIR to MIR as the former and the later emitted from cold dusts in dusty star-forming regions and hot dusts in tori around AGNs, respectively. These classified LIRGs with higher AGN activities show lower specific SF Ratio (sSFR). The SF/AGN distinction of these AKARI classified LIRGs becomes recently confirmed by using Chandra data (Krumpe+2015). The IR SED analysis is a unique technique for studying co-evolution of dusty SF and AGN activities with dusty tori. I will discuss the hidden connection between dusty starbursts and AGNs, adding recent radio observational results obtained with the JVLA.

2015 Mar 10 14:00

Special Seminar: Claudia Conrad


Open Cluster Groups and Complexes

It is generally agreed upon that stars typically form in open clusters and stellar associations, but little is known about structures in the Galactic open cluster population. Do open clusters and stellar associations form isolated or do they prefer to form in groups? Answering this question would provide new insight into star and cluster formation, as well as to the structure and evolution of our Milky Way. In the past decade the studies of open clusters groupings were either based solely on spatial criteria or also included tangential velocities for the identification of structures. Our approach was that genuine open cluster grouping would occupy a well defined area in the sky and show similar velocity vectors. Thus, it was only reasonable to use 6D phase-space information for the identification of open cluster groupings. We explored the Catalogue of Open Cluster Data (COCD) and could determine 6D phase-space information for 432 out of the 650 listed open clusters and compact associations. The group identification was performed using an adapted version of the Friends-of-Friends algorithm with linking lengths of 100 pc and 10-20 km/s. For the verification of the identified structures we applied Monte-Carlo simulations with randomised samples. The majority of the found gropings were pairs, accompanied by a few groups and one larger complex. The Monte-Carlo simulations revealed that the larger groups and the complex are most likely genuine, whereas the pairs are more likely to be by chance alignments. A closer look at the characteristics of the detected open cluster groupings suggested that they are likely to originate from a common molecular cloud.

2015 Mar 06

Jenny Sorce


Cosmic Flows observations give us CLUES to the formation of the Local Universe

Our Local Universe, the best-observed volume of the Universe, provides an excellent sample with which we can test gravitational theories and attempt to understand the formation and evolution of our neighborhood. Using recently released data - positions and peculiar velocities of more than 8,000 galaxies from the second catalog of the Cosmicflows project - and a newly developed technique - the reverse Zeldovich approximation and a bias correction, we produce simulations which resemble the Local Universe. The resulting Constrained Local UniversE Simulations reproduce the Large-Scale Structure down to a few megaparsecs (typically 3-4 h-1 Mpc). Local observations and constrained simulations can therefore be efficiently compared.

2015 Mar 05

Special Seminar: Antonio Garcia Munoz


Radiative transfer in planetary atmospheres: A Pre-Conditioned Backward Monte Carlo algorithm

The interpretation of polarized radiation emerging from a planet atmosphere must rely on solutions to the vector radiative transfer equation (VRTE). Monte Carlo integration of the VRTE is a valuable approach for its flexible treatment of complex viewing and/or illumination geometries, and it can intuitively incorporate elaborate physics. In this talk, I will present a novel pre-conditioned backward Monte Carlo (PBMC) algorithm for solving the VRTE. As classical BMC methods, the PBMC algorithm builds the solution by simulating the photon trajectories from the detector towards the radiation source, i.e. in the reverse order of the actual photon displacements. The neglect of polarization in the sampling of photon propagation directions in classical BMC algorithms leads to unstable and biased solutions for conservative, optically thick, strongly polarizing media such as Rayleigh atmospheres. The numerical difficulty is avoided by pre-conditioning the scattering matrix with information from the scattering matrices of prior (in the BMC integration order) photon collisions. Pre-conditioning introduces a sense of history in the photon polarization states through the simulated trajectories. Since the convergence rate for MC integration is independent of the integral’s dimension, the scheme is a valuable option for estimating the disk-integrated signal of stellar radiation reflected from planets. Such a tool is relevant in the investigation of both exo- and solar system planet phase curves. Examples of ongoing work on the investigation of planet phase curves will be presented.

2015 Mar 03 14:00

Special Seminar: Sami Dib

(Niels Bohr Institute, Denmark)

The Milky Stellar Clusters meet statistics: Evidence for a non-universal IMF

I will present the results from two complementary studies that investigate the shape and universality of the IMF among Galactic stellar clusters. In the first study the universality of the IMF is tested using a sample of eight young stellar clusters IC 348, ONC, NGC 2024, NGC 6611, NGC 2264, ρ Ophiuchi, Chameleon I, and Taurus). I will show that the posterior probability distribution functions (pPDFs) of the IMF parameters, inferred using Bayesian statistics techniques, do not overlap within the 1-sigma uncertainty limit as well as with the value of the parameters for the Galactic field IMF. In the second study, the high mass star content of a larger survey of Galactic clusters is used to further test the universality of the IMF. In addition to confirming the IMF is not universal, the results of this study put strong constraints on the shape of the Galactic cluster mass function and rule out the existence of a cluster mass-maximum stellar mass relation.

2015 Feb 27 10:30

Alessandro Lanzafame

(Dipartimento di Fisica e Astronomia, Università di Catania, Italy)

Gaia-ESO survey science validation: first results on young open clusters

The Gaia-ESO Spectroscopic Survey is obtaining high-quality spectroscopy of some 100,000 Milky Way stars using the FLAMES spectrograph at the VLT, down to V=19 mag, systematically covering all the main components of the Milky Way and providing the first homogeneous overview of the distributions of kinematics and chemical element abundances in the Galaxy. Observations of young open clusters, in particular, are giving new insights into their initial structure, kinematics, and their subsequent evolution. In this talk I shall describe the analysis of UVES and GIRAFFE spectra acquired in the fields of young clusters whose population includes pre-main sequence (PMS) stars. The analysis is applied to all stars in such fields, regardless of any prior information on membership, and provides fundamental stellar atmospheric parameters, elemental abundances, and PMS-specific parameters such as veiling, accretion, and chromospheric activity. Science validation of our analysis on the first two years of observations has lead to interesting results on the kinematic structure of two young (~10 Myr) open clusters as well as on accretion and chromospheric activity on an extensive sample of PMS stars in the first five young open clusters observed.

2015 Feb 20 11:00

Fourth Potsdam - Berlin Astronomical Colloquium

(at Potsdam University)


  • 11.00 - 11.30 Cecilia Scannapieco (Leibniz-Institut AIP): "Cosmological simulations of galaxy formation"
  • 11.30 - 12.00 Martin Wendt (Uni Potsdam): "IGM, ISM & DIBs in absorption"
  • 12.15 - 13.30 Mittagspause, Mensa Golm
  • 13.30 - 14.00 Michael Schulreich (TU Berlin): "Investigating the link between an iron-60 anomaly in the deep ocean’s crust and the origin of the Local Bubble"
  • 14.00 - 14.30 Marek Kowalski (HU Berlin): "Experimental Cosmology at the Humboldt-University Berlin"
  • 14.30 - 15.00 Kathrin Egberts (Uni Potsdam): "Gamma-Ray Astronomy with H.E.S.S."
2015 Feb 13 10:30

Brad Gibson


Building Spiral Galaxies with Supercomputers

The history of disk galaxy simulation is dotted with remarkable successes, tempered by frustrating impasses, including an inability to recover anything remotely similar to the Milky Way. Recent advances suggest that we might have made a breakthrough by generating essentially bulgeless disks. I will examine the evidence for this new-found optimism and identify where the shortcomings suggest we should be concentrating our future efforts.

2015 Feb 06 10:30

George Kordopatis


Galactic archaeology: latest observational results on the Milky Way formation mechanisms

Galactic archaeology aims to unravel the sequence of events that have taken place during the history of the Milky Way, in order to understand how our Galaxy evolved. The investigation is done by analysing fossil records (metallicity and orbits) of stellar populations old enough to probe the initial formation stages of the Milky Way. In this talk I will review the recent progress in our understanding of the formation of the old stellar disc and the galactic bulge. Based on the large spectroscopic surveys like RAVE (data-release 4: ~500,000 spectra) and Gaia-ESO (DR2:~20,000 stars) I will show how the observations manage to constrain the formation mechanisms of the galactic components, requiring both internal galactic evolution and external accretion of satellite galaxies. The talk will end with a brief overview of the use of the future data to come (e.g.: Gaia, 4MOST).

2015 Feb 03 15:00

Special Seminar: Bruno Henriques


Galaxy formation in the Planck Cosmology - Matching the observed evolution of star-formation rates, colours and stellar masses

I will present results from the recent major release of the Munich galaxy formation model. In addition to the new PLANCK cosmology, significant modifications to the physics were implemented in order to fix major problems identified in previous versions. These include the too early formation of low mass objects and their too passive populations at later times. I will show how the new physics result in a model that is consistent with the observed evolution of the stellar mass functions of all, red and blue galaxies from z=3 to z=0, while matching the evolution of the star formation rate densities and the main sequence of star formation across the entire observable mass range. I will connect the different evolution of low and high mass galaxies to the efficiency of the star formation quenching processes included in the model such as AGN radio mode feedback and environmental effects across cosmic time. I will then detail the plans we have to extend the predictive capabilities of this model to the key areas required to interpret new observational surveys that promise to revolutionize our knowledge of galaxy formation. These include resolved studies of molecular gas from sub-millimetre telescopes, and ionised gas and stellar populations from high-resolution multi-object spectrographs. To provide theoretical insights to these observations, models have to resolve the internal distribution of stars and gas while following different hydrogen phases and heavy elements.

2015 Jan 23 10:30


Who does what?

The fourth round of speakers:

Horst Balthasar, Thorsten A. Carroll, Giovanni Guidi,
Eloy Luis Hernandez Anguizola, Arto Järvinen, Roelof de Jong,
Thiago Junqueira, Francisco Kitaura, Philipp Kummerow,
Georg Lamer, Umberto Maio, Gal Matijevic,
Alexey Mints, Martin Mitzkus, Justus Neumann,
Alejandro Paredes, Daniel Phillips, Pierre-Antoine Poulhazan,
Andreas Rabitz, Jürgen Rendtel, Kristin Riebe,
Monika Rutowska, Martin M. Roth, Ilya Ilyin,
Gabriele Schönherr

You can download the talks here (pdf, 12 MB).

2015 Jan 22 15:00

Special Seminar: Wojciech Hellwing


Probing the nature of Dark Matter and Dark Energy: from the Local Group to the Local Universe

Cosmology asks fundamental questions about the structure and composition of the Universe, its birth, evolution and future fate. The current understanding is encapsulated in a well established concordance cosmological model, the LCDM (Lambda Cold Dark Matter) model, whose parameters have been measured to remarkable precision. Nonetheless, the current cosmogony is characterized by several fundamental puzzles about the physical nature of the Universe. The most important questions concern the nature of the two components that dominate the evolution and fate of the Cosmos: Dark Matter (DM) and Dark Energy (DE). In my talk I will discuss my research focusing on possible ways of extracting the information about the physical nature of the DM and DE components using observations of the Local Universe (LU). Our cosmic neighbourhood stretches from the "backyard" dwarf galaxies of the Local Group (LG) to the relatively nearby galaxies woven into the Cosmic Web extending up to hundreds of Megaparesecs around us. The main topic of my talk will be twofold: (i) how we can explore the information encoded in the peculiar motions of local galaxies to study the nature of the DE and gravity; (ii) and how we can use the connection between the larger-scales and the local neighbourhood to get insights into the physical nature of DM and LCDM specific characteristics of galaxy formation.

2015 Jan 16 10:30

Thiago Junqueira


Disk resonances and a new method for estimating the pattern speed of the MW spiral arms

The resonances play an important role in the evolution of the disks of spiral galaxies, and in particular, of our Galaxy. Its effect on the chemical abundance gradients is even a tool to estimate the age of the present spiral arm structure, which we find to be long-lived, contrary to a recent common belief. One expected effect of corotation resonance is a minimum of star formation associated with the minimum velocity at which the interstellar gas feeds the spiral arms (seen as potential wells and star-formation machines). The 4:1 resonance also plays an import role in our Galaxy and it might be responsible for some bifurcations that appear as short arms, as we'll show. However, one of the fundamental parameters of the spiral structure, which determines the location of all resonances in the disk, is its angular velocity or pattern speed. In here we propose a new method based on the interaction between the spiral arms and the stars in the disk. Using a sample of around 600 open clusters and 500 giant stars observed by APOGEE DR10, we found Ωp = 23.0 ± 0.5 km s −1 kpc −1. This is in close agreement with a number of studies which suggest values in the range 20-25 km s −1 kpc −1.

2015 Jan 13

Special Seminar: Richard McDermid

(Macquarie University / Australian Astronomical Observatory, Sydney, Australia)

Star Formation Histories and varying IMF of Early-Type Galaxies from Atlas3D

The Atlas3D Survey comprises spatially-resolved spectroscopic data for a complete, volume-limited sample of 260 early-type galaxies observed within the local 40 Mpc volume. This K-band selected sample spans a range in mass from 10e10 to 10e12 solar masses, and probes two orders of magnitude in local galaxy density, giving a large range in mass and environment. Our integral-field spectroscopy covers on average more than one effective radius, providing a complete picture of most of the stellar content of these objects. I will present recent results analysing the global star formation histories of these objects as a function of mass and environment, and explore evidence for a systematically varying IMF normalisation as derived from a combined dynamics and stellar population approach.

2014 Dec 17 14:00

Special Seminar: Carolina von Essen

(SAC Aarhus, Denmark)

Exoplanet characterization using ground-based observations

During its four years of photometric observations the Kepler space telescope has detected thousands of exoplanet candidates. One of Kepler's most intriguing tools has been the confirmation and characterization of multiplanet systems via Transit Timing Variations (TTV). Unfortunately there are many interesting multiplanet candidate systems displaying TTVs on such long time scales that the existing Kepler observations are not sufficiently long enough to confirm and characterize them. Therefore we have organized KOINet, a near-global photometric follow-up network consisting of $\sim$20 middle-sized telescopes distributed in longitude between the United States and China. KOINet will allow almost 24 hours of continuous monitoring. Over the next years we will use KOINet to follow-up long period TTV systems to confirm and characterize them. Here I will mostly present the current status of KOInet and first results.

2014 Dec 16 11:00

Special Seminar: Mickael Rigault

(HU Berlin)

Environmental dependencies in Type Ia supernova luminosity, and their consequences on cosmological measurements

Use of Type Ia supernovae (SNe Ia) as distance indicators has proven to be a powerful technique for measuring the dark energy equation of state and the Hubble Constant. However, their progenitor remains largely unknown and bias may arise from unaccounted for stellar variation that could impact the way the progenitor-star evolves in SN Ia.

In this talk I will present the results of a study of host galaxy regions in close proximity to SNe Ia. We find a significant offset in SNe~Ia standardized magnitude between these from locally star-forming regions and those from passive regions. (Rigault et al 2013) Since the fraction of SNe Ia from passive region is expected to decrease with redshift and/or to vary between samples, such a magnitude bias, introduces a bias in distance measurements using these standardizable candles.

We discover that this effect impacts the measurement of the Hubble by 3%, which explains the current tension between the indirect- (from CMB) and direct-measurements of this constant. (Rigault et al submitted)

Systematic errors are today dominating the error budget of cosmological constant measurement (such as w). In this context, local host informations of SNe~Ia are precious to better understand this probe. In the near future, these informations will enable us to improve their use as standardisable candles. As an example, I will show that a simple environmental selection of SNe Ia allow to significantly reduce the dispersion of the Hubble diagram by 30%.

2014 Dec 12


Who does what?

The third round of speakers:

Joar Brynnel, Detlef Elstner, Harry Enke,
Yori Fournier, Marcus Gellert, Gohar Harutyunyan,
Swetlana Hubrig, Silva Järvinen, Ondrej Jaura,
Josephine Kerutt, Arman Khalatyan, Jochen Klar,
Georges Kordopatis, Davor Krajnovic, Manfred Küker,
Andreas Künstler, Noam Libeskind, Adriane Liermann,
Matthias Mallonn, Adriana Mancini Pires, Gottfried Mann,
Ivan Minchev, Benito Moralejo, Alessandro Mott,
Jan Peter Mücket, Volker Müller, Sebastian Nuza,
Hakan Önel

You can download the talks here (pdf, 90 MB).

2014 Dec 11 14:00

Special Seminar: Hans Zinnecker

(Deutsches SOFIA Institut, Univ. Stuttgart, Germany and SOFIA Science Center, NASA-Ames, Moffett Field, USA)

SOFIA - past, present, and future

SOFIA, the Stratospheric Observatory for Infrared Astronomy, which carried out first science flights in mid 2010, has finally reached full operational capability in April 2014. In the second half of 2014, the plane has undergone a major structural overhaul at Lufthansa Technik in Hamburg. It is now back at its base in Palmdale, southern California.

Cycle 3 observing time (80% US, 20% Germany) has been awarded and some 80 flights will be carried out in 2015, including a southern deployment to New Zealand and a Pluto occultation near Australia (June 29, 2015). In this talk, I will summarize the current status of SOFIA, its instrument suite, and some of the recent science highlights of Cycle 1 and 2 (e.g. star formation and astrochemistry). After a difficult year in terms of NASA support, SOFIA is getting back into gear poised to continue delivering unique mid- and far-infrared science, in the post-Spitzer and post-Herschel era.

You can download the talk here (pdf, 8.7 MB).

2014 Dec 09 14:00

Special Seminar: Henry Aurass


Particle acceleration sites during solar eruptive processes

In 2002, Aurass, Vrsnak and Mann described an enigmatic bright flare radio source occurring during the impulsive flare phase (and sometimes again about ten minutes later) suggesting a radio shock signature without frequency drift. Cases with imaging data revealed a height between 0.3 and 0.4 Rs above the flaring active region at frequencies between 200 and 350 MHz, well above expectations based on coronal density models. Despite of clear and reproduced observational evidence there was much doubt about this finding (and speculations about radio signature of a standing reconnection outflow shock) in the community. In two recent papers (A&A 2013, Solar Phys. 2014) the study of a limb event led to the understanding of the physical nature of these sources. I will explain the essence of both papers and discuss its consequences for models of solar eruptive processes and coronal particle acceleration sites.

2014 Dec 05 10:30



Research Environments, Data Publication and the Virtual Observatory

E-Science develops and builds tools and infrastructure for the scientific workflow. With current observing and compute facilities the data size and the methods to work on this data is changing. For maximizing the scientific output from these data, interaction of a variety of specialized scientists is required.
E-Science at AIP focuses on the following topics:
- Collaborative Research Environments (e.g. CLUES, MUSE)
- Data Publication (e.g. CosmoSim, RAVE)
- Virtual Observatory (Interfaces for databases)
Additionally, in a hands-on session in the afternoon 13:30 - 15:00, we give a short SQL intorduction, show how to access the RAVE and CosmoSim databases, demonstrate some VO Tools, and how to use the Data Access Service.
If you want to actively participate in the afternoon session, please bring a laptop with Topcat and Aladin installed. (If you need help with this, please contact us beforehand. We won't have time to fix installations during the session.)

You can download the talk (pdf, 17 MB) and the tutorials (pdf, 2.5 MB).

2014 Nov 28 10:30

Francisco Kitaura


Modelling and inferring the cosmological large-scale structure from galaxy redshift surveys

The imprints of the origin and cosmic evolution of our Universe are encoded in the cosmological large-scale structure. However, the action of gravity after billions of years has washed out this information. Moreover our observations yield only a discrete and distorted luminous fraction of biased tracers of the continuous underlying cosmic (dark) matter density field. How accurately can we model the biased galaxy distribution including redshift space distortions and nonlinear clustering?, How far can we undo gravity?, and How far can we recover the full phase-space information from such tracers?

2014 Nov 24 11:00

Special Seminar: Ales Kucera

(Astronomical Institute of the Slovak Academy of Sciences, Tatranska Lomnica)

Research of the solar corona at Lomnicky Peak Observatory

We introduce a historical overview of an investigation of the solar corona at the Lomnický Peak Observatory including a description of the older observational infrastructure.

In the second part of the talk we show scientific data and results and we will describe new infrastructure (Coronal Multichannel Polarimeter and Solar Chromospheric Detector) and plans for future.

2014 Nov 21

Tim Brown

(Las Cumbres Observatory)

Dancing with the Stars: How Do They Spin the Way They Do?

All stars rotate, with periods ranging from milliseconds (for some neutron stars) to years (for some supergiants). Cool main-sequence stars with surface convection zones (Sun-like stars) show less range, but still span periods from fractions of a day to months. Our current understanding says that young stars rotate rapidly, but are eventually spun down by the torque from a magnetized stellar wind. To explain the details of rotational period distributions in not-too-old star clusters, the theory invokes other processes, notably a moderately long-lived (few hundred MY) decoupling of the rotation of the stellar convection zone from that of the interior. In this talk, I will first review the observational and theoretical arguments that lead to this picture. Then I will describe a modest variant (of mine) to an alternative explanation for the observations that was first suggested by Sydney Barnes. This variant retains the notion of magnetized wind braking but does not require young-star convection zones to rotate independently of their radiative interiors. A desirable feature of this view is that if it is shown to be correct, we may as a result learn something fundamental about stellar dynamos. Last, I will discuss how one might choose between these two pictures. Unsurprisingly, time-domain observations are the key; LCOGT's world-wide network of robotic telescopes is ideally suited to provide much of the necessary data.

2014 Nov 20 14:00

Special Seminar: Tim Brown

(Las Cumbres Observatory)

Las Cumbres Observatory: The Network Comes Alive!

Las Cumbres Observatory Global Telescope is an observatory headquartered in Goleta CA, with ties to UC Santa Barbara, created in 2005 to pursue studies in time-domain optical astronomy. "Time domain astronomy" covers many subfields, ranging from near-Earth asteroids to supernovae/cosmology. What these specialties have in common is the need to observe their targets at will, anywhere in the sky, any time (and in some cases, all the time). Traditional ground-based observatories and scheduling models are a poor fit to this kind of observing. LCOGT is responding to this disconnect by building a coordinated world-wide network of robotic telescope clusters, designed and instrumented to attack the most critical issues in the time domain. Since mid-2012, six years of development work have suddenly condensed into working telescopes and instruments: two spectrographs on our original 2m telescopes, nine new 1-meter telescopes in Texas, Chile, South Africa, and Australia, six cross-dispersed echelle spectrographs under construction, and possible further expansion in the works. In this talk, I will first describe the science goals of LCOGT (illustrated with recent results), and then lead you on a tour of our newly-expanded facilities for achieving these goals.

2014 Nov 14

Alexander Kashlinsky

(NASA Goddard Space Flight Center)

The near-IR cosmic background from first stars: from Spitzer to Euclid and JWST

I will review the current theoretical understanding of the first stars and black holes and their potential contributions to the Cosmic Infrared Background (CIB) during the emergence of the Universe out of the "Dark Ages". Intriguing indications of the possible emissions from these objects have been obtained over the last several years from CIB fluctuation measurements using Spitzer/IRAC deep images. The uncovered source-subtracted CIB fluctuations substantially exceed those from remaining known populations. The spatial spectrum of these fluctuations is consistent with populations clustering according to high-z LCDM model. The SED of the CIB fluctuations is blue and consistent with emissions produced by hot objects at high z. Cross-correlation analysis with Chandra X-ray data suggests that the unresolved CIB and CXB are coherent at a remarkably high level implying fractional abundance of black holes, among the emitters of the CIB, which significantly exceeds that in known populations. I will also discuss a new CIB project, LIBRAE (Looking at Infrared Background Radiation Anisotropies with Euclid), planned by NASA and ESA for the future Euclid satellite mission. I will review how LIBRAE will identify the net emissions from the first stars era, lead to a better understanding of the condition of intergalactic medium at that epoch in combination with the existing CMB data, and isolate the contributions from the first black holes in conjunction with X-ray data. A significant and unique further information can be provided with CIB measurements from JWST.

2014 Nov 13

Special Seminar: Elisabetta Caffau

(Observatoire de Paris/Meudon)

The first generations of stars

Extremely metal-poor (EMP) stars are the descendents of the massive stars of the first stellar generation. Their chemical composition reflects the early phases of the Universe: on one side, it puts constraints on the masses of these first-generation massive stars, and on the other side it allows us to better understand the formation of low-mass stars from a gas cloud depleted in metals. EMP stars are are a minor component of the present stellar population (about one thousandth) and special efforts are required to find them. We exploited the Sloan Digital Sky Survey to search for EMP candidates with the colors of turn-off stars. We subsequently observed them at medium- and high-resolution to derive their chemical composition.

2014 Nov 13

Special Seminar: Paul Jorden / Pierre Chazan

e2v: CCD and CMOS technology developments for astronomical sensors

Recent development in the technology of silicon sensors for astronomical applications. Novel CCD and CMOS sensors have been designed for low noise and high sensitivity astronomical use. High resistivity sensors allow thicker silicon for higher red sensitivity in several types of new CCD. The capability to manufacture large sets of CCDs to form large focal planes has allowed several very large mosaics to be built for astronomy with increasing formats on the ground and in space. In addition to supplying sensors we discuss increasing capacity and interest in the commercial supply of integrated "camera" systems.

2014 Nov 10 11:00

Special Seminar: Fabio Iocco

(Instituto de Fisica Teorica, IFT)

The dark matter profile of the Milky Way

Spiral Galaxies are known to be dark matter dominated systems, and one of the most outstanding astrophysical proofs of its existence. Yet retrieving information about the the dark matter distribution in our very own spiral Galaxy, the Milky Way, is quite challenging.

I will show how a new set of analysis of purely observational data permit to draw strong model-independent conclusions on the presence of DM in the Milky Way, and sketch its distribution while getting rid of theoretical bias. These new results are competitive with those of existing methods, and open up an interesting avenue for the study of the dark matter profile of the Milky Way with forthcoming observational results.

2014 Nov 07 10:30

Yori Fournier


A universal relation for a compressible model of rising flux tubes in low mass stars.

During this colloquium I will discuss the main issue of my thesis, namely rising magnetic flux tubes. We are Interested about active regions, and try to explain some of the recurrent characteristics we observe. I am going to present the numerical model we designed. And show that it suggests that low mass stars follow a universal relation. As well as it provides predictions which can be used to challenge the theory.

2014 Oct 28 14:00

Paola Oliva-Altamirano

(Swinburne University/Australian Astronomical Observatory)

Brightest Cluster Galaxies as probes of galaxy formation

Brightest group and cluster galaxies (BGGs/BCGs) are old giant ellipticals, which have been show to be different from any other cluster galaxy. Despite of being easy detectable their formation and evolution is still poorly understood. I will present a statistical analysis of a large sample of 883 Brightest group and cluster galaxies (BGGs/BCGs) from the Galaxy and Mass Assembly Survey (GAMA). We analyse their stellar mass growth, position in the cluster, and the percentage of BGGs/BCGs that show H\alpha in emission. We find that BCGs grow steeply until z~0.5, and slow down at lower redshift.

BCGs have been predicted to have a more active accretion history than less massive galaxies. We further use IFU spectroscopy to study the spatially-resolved stellar populations of BCGs and their connection with galaxy's angular momentum. We find that all the BCGs in our sample have gone through at least one major merger after z=1. Our stellar population analysis suggest that BCGs have a more active accretion history than early-type galaxies of similar mass.

2014 Oct 17 10:30

Enn Saar

(Tartu Observatory)

Measuring clustering in the galaxy distribution

Measuring galaxy clustering has been a long time the main tool for understanding the large-scale structure of the Universe. In the early days it allowed us to understand the main features of the structure, its dynamics and evolution. Nowadays we are seeking for much finer details in clustering -- a good example is the discovery of the traces of baryonic oscillations. As those traces are tiny, it is very important to assure these are real -- we must know well how our statistics behave. I will try to convince you that sometimes the estimation of errors might be interesting, too.

2014 Oct 14 11:00

Special Seminar: Alexis Rouillard

(CNRS, IRAP, Toulouse, France)

Probing the origin of solar energetic particles using combined remote sensing and in-situ measurements

The origin of the most energetic solar particles released during solar storms is still debated. In this study, combined observations and modelling techniques are used to test the hypothesis that the most energetic solar energetic particles (SEPs) are accelerated by coronal shock waves. Combined STEREO SOHO and SDO observations allow us to reconstruct the 3-D extent of pressure waves formed during the eruption of coronal mass ejections. We concentrate on the proton-rich events detected by the near-Earth spacecraft and the STEREOs between 2011 to 2014. The SEPs measured in situ during these episodes of propagating coronal waves propagate along coronal and interplanetary magnetic field lines between the Sun and 1 AU. We use a combination of observations and modelling to reconstruct the 3-D location of magnetic field lines and thereby establish the magnetic connectivity between the shock near the Sun and the points of in-situ measurements near 1AU. This 3-D localisation allows us to determine the (1) the height and spatial extent of the pressure waves at the SEP release times near the Sun, (2) compare the longitudinal extent of SEP events with the extent of the pressure waves. We combine a 1D Solar Wind hydrodynamical code (VP code) with a potential model of the solar corona to compute the density, bulk speed, ion and electron temperatures and pressures along the relevant magnetic flux tubes. This allows us to compute the characteristic speeds of the medium and the fast and slow-mode speeds at the potential shock transition. We compare the properties of the inferred shocks with those of the SEPs measured in situ.

2014 Oct 10 10:30

Antonino Lanza

(INAF, Catania Astrophysical Observatory)

Interactions between late-type stars and close-in planets

Late-type stars have outer convection zones where hydromagnetic dynamo action can develop and tides can effectively dissipate kinetic energy. Therefore, close-in planets can interact with stellar magnetic fields, while their orbital evolution is ruled by tides and planet-planet gravitational interactions in systems with more than one planet. I shall introduce some selected observations that can provide information on the magnetic or tidal interactions between planets closer than about 0.1 AU and their host stars. Then I discuss some models proposed to account for those observations.

2014 Oct 09 11:00

Special Seminar: Klaus G. Strassmeier


PEPSI arrives at the LBT

2014 Sep 26

Jörg Weingrill


Ages of Open Clusters with STELLA

IC4756 is an open cluster in the CoRoT field, and with an age of 800 Myr neatly splits the difference in age between the well-studied Hyades (625 Myr) and NGC 6811 (1 Gyr) clusters. Consequently its rotation periods should lie between those of the Hyades and NGC 6811, independent of an theoretical model, if rotation is indeed a well-defined function of stellar age and mass. Therefore we have performed precision time-series photometry of the IC4756 field for almost 73 days with the CoRoT satellite, and derived 348 main sequence rotation periods in the cluster region. Radial velocity measurements taken with WIYN+Hydra together with multi-color Strömgren photometry using the STELLA robotic telescopes on Tenerife allowed us to identify about 200 cluster members and to compare age-determinations stated by different theories. To date, the cluster member rotation periods indeed lie between those of the Hyades and NGC 6811. The corresponding cluster age is 720 Myrs. We will also present photometry and rotation periods from the Stella Open Cluster Survey (SOCS) from several clusters including NGC 1647, NGC 6633 and M 48.

2014 Sep 23 14:00

Special Seminar: Kevin Croxall

(Ohio State)

Oxygen in the Local Universe: Error and Uncertainty in Abundances

The metal content of a galaxy is one of the most important properties used to distinguish between viable evolutionary scenarios and strongly influences many of the physical processes in the ISM. An absolute and robust calibration of extragalactic metallicities is essential in constraining models of chemical enrichment, chemical evolution, and the cycle of baryons in the cosmos. Despite this strong dependence on abundance, the calibration of nebular abundances from nebular emission lines remains uncertain. Different calibrations of the abundance scale require different assumptions, which may or may not be valid, and measurements, not all of which are easily obtained. MODS on LBT and the late Herschel Space Observatory are allowing us to clarify this long standing calibration uncertainty. The sensitivity of MODS is enabling the detection of numerous temperature sensitive lines and features in nearby galaxies and Herschel observations of the [O III] 88 micron fine structure line in nearby galaxies are enabling the determination of nebular abundances that are nearly independent of temperature. I will discuss current efforts at constraining the abundance scale using these modern facilities.

2014 Sep 19 10:30

Klaus Dolag


The Magneticum Pathfinder Simulations

Upcoming astronomical surveys and instruments like Planck, SPT, PanStars, DES, Euclid, LOFAR, eRosita and many more will need a theoretical counterpart in form of simulations which follow the formation of cosmological structures in so far unaccomplished detail, taking into account enough physical processes to allow a self consistent comparison to observations at multiple wavelength and throughout the entire epoch of structure formation. I will report on preliminary results from a recent simulation campaign, where we followed the formation of cosmological structures in so far unaccomplished detail, performing a large set of cosmological, hydrodynamical simulations covering up to Gpc^3 volumes, taking into account enough physical processes (star-formation, chemical enrichment, AGN feedback) to allow a self consistent comparison to observations at multiple wavelength.

You can download the talk here (pdf, 38 MB).

2014 Sep 18

Special Seminar: Karin Muglach

(Goddard Space Flight Center)

Properties of Coronal Hole Jets and Outflows as Observed With SDO and Hinode

Solar coronal holes are known to be the source of the fast solar wind (as observed with in-situ instruments near Earth). Although generally darker than surrounding quiet and active regions, they contain small-scale bright areas. In low-resolution coronal images these areas were called bright points, but modern high-resolution images show that they consist of tiny loop-like coronal structures with a bipolar magnetic field distribution at their photospheric footpoints. X-ray and EUV imaging instruments have shown in the past that these bright points undergo episodic ejection of mass, coronal hole jets.

In this presentation I will show an analysis of these coronal hole jets observed with Hinode/EIS and SDO. Coronal velocities of up to 200 km/s and enhancements in line width are measured. On the other hand, some of these jets are hardly visible in imaging data like SDO/AIA and Hinode/XRT.

I will also discuss the photospheric signatures at the footpoint of these jets using SDO/HMI magnetograms and the plane-of-sky flow field derived with local correlation tracking. Both the evolution of the magnetic field and the flows allow us to study the photospheric drivers of these jets. I will give both a summary of all events observed in a 44h time series and a discussion of a couple of events in detail. This allows us to address the question of the origin of the solar wind and its relation to the magnetic field.

This work is funded by the National Science Foundation.

2014 Sep 12


Who does what?

The second round of speakers:

Sydney Barnes, Stuart Ian Barnes, Simona Bekeraite,

Frank Breitling, Omar Choudhury, Harendra Fernando,

Joris Gerssen, Domenico Giannone, Sergio Javier Gonzalez Manrique,

Stefan Gottlöber, Thomas Granzer, Quan Guo,

Dionne Haynes, Roger Haynes, Christian Herenz,

Anne Hutter, Thomas Jahn, Katja Janßen,

Andreas Kelz,

You can download the talks here (pdf, 38 MB).

2014 Sep 05

Daniel Ceverino

(Universidad Autonoma de Madrid)

The role of cold flow accretion in Galaxy Formation

The flow of gas from the cosmic web into galaxies provides the necessary fuel for star formation and galaxy assembly. I will review our current knowledge about gas accretion into galaxies and its consequences for galaxy formation at high and low redshifts. Special attention will be given to the detectability of cold streams as Lyman-alpha blobs or Lyman-Limit systems, as well as the current challenges to the cold-flow picture.

2014 Sep 01 11:00

Special Seminar: Robert Nikutta

(PUC, Santiago)

The Weather around Active Galactic Nuclei - From X-rays to IR

The evidence for clumpiness of the gaseous, dusty medium surrounding the central AGN engine is mounting. There is growing consensus that the distribution of material is not smooth, at least not all of it. I will introduce the CLUMPY radiative transfer models for AGN tori (Nenkova et al. 2002,2008) and show how we use them to understand the observational evidence, both in X-rays and in the IR domain. Analyzing 16 years of X-ray observations in AGN with RXTE, we recently found 12 secure eclipse events and several candidates. In a recent paper (Markowitz, Krumpe, Nikutta, 2014) we show that these events are discrete gas+dust clouds crossing our line of sight. Due to RXTE's long mission duration, it was sensitive to eclipses caused by clouds much further away from their AGN than previously reported events. Our clouds are located both in the BLR and also well into the dusty part of the cloud distribution, the "torus". Because the number of events found by RXTE is quite large, we were able to perform a statistical analysis and derive "instantaneous" probabilities to observe an AGN in an obscured state. In a follow-up (Nikutta, Krumpe, Markowitz, in prep.) we constrain the properties of the clouds further, and test the predictions of most recent AGN torus models. Using Bayesian inference together with the CLUMPY models, we can derive most of the parameters that govern the distribution of clouds in the BLR and in the torus. This provides a natural connection between the AGN X-ray light and the Infrared emission, a signature of the dusty AGN torus. I will show how using the large WISE catalog we can reliably identify type-1 and type-2 AGN through their IR properties, putting AGN unification to the test.

2014 Jul 18 11:00

Special Seminar: Charles Kuhen

(University of Sydney, Australia)

RR Lyrae As Cosmic Swiss Army Knives

RR Lyrae stars are old, radially pulsating stars located on the horizontal branch which have long been used as cosmic distance indicators. More recent work has shown that RR Lyrae are useful tools for studying a wide variety of topics in stellar, galactic, and extragalactic astronomy. In this talk, I will discuss ongoing work in these different areas that is utilizing RR Lyrae and how these stars can be used to help identify substructures in the Milky Way halo, better understand how the halo was formed, and to look at mass transfer between binary stars.

2014 Jul 04 10:30

Marco Limongi

(INAF - Osservatorio Astronomico di Roma)

Presupernova evolution, explosion and nucleosynthesis of rotating massive stars at various metallicities

I will present an overview of the evolution of massive stars from the pre main sequence phase up to the onset of the iron core collapse, their hydrostatic and explosive nucleosynthesis and their final fate. The models extend in mass between 13 and 80 Msun, have initial metallicities corresponding to [Fe/H]=0,-1,-2,-3 and have initial rotation velocities corresponding to v=0, 150 and 300 km/s.

2014 Jun 27 10:30

Lars Koesterke

(Univ. of Texas Austin)

The Astronomer's workplace is changing. Why should I care?

For good reasons many astronomers have ignored changes in computer architecture in the past. However, the next change combined with a shift towards Big Data in 'traditional' astronomy may force us to pay more attention. My talk will be mostly geared towards the non-HPC astronomer. I will introduce the basics concepts of new hardware architectures that will soon leap from high-end accelerators (GPUs and Xeon Phi) into our desktops, and will present an astronomer's view on what the changes in hardware and the shift towards Big Data may mean for our community.

2014 Jun 20 14:00

Third Potsdam - Berlin Astronomical Colloquium


14:00 Matthias Steinmetz (AIP) - Welcome address

14:05 Wolf-Christian Müller (TUB) - Investigation of plasma turbulence

14:35 Helge Todt (UP) - Hydrogen deficient central stars of planetary nebulae

15:05 Cristina Chiappini (AIP) - New observational constraints to MW chemodynamical models

15:35 Coffee break

16:05 Igor Telezhinsky (UP) - Cosmic rays and their radiation in young supernova remnants

16:30 Rainer Arlt (AIP) - Magnetic fields on stars - stability, activity and dynamos

17:00 Bier & Grillwürstl

2014 Jun 18 11:00 Special Seminar: Alexander Grossman

(HTWK Leipzig)

New Perspectives in Scientific Publishing

How will scientific publishing develop in the 21st century? Over the last decades topics such as Journal Impact Factor, blind peer-review and library subscriptions have dominated the discussion. However the digital revolution has already begun to change the rules. New topics such as "article- level-metrics", "post-publication peer review" and "open data" have emerged and every single day four new Open Access journals are founded. Open Access is becoming publicly mandated in the US and EU, encouraging researchers to submit their work to open repositories. Preprint servers and subject repositories such as arXiv or bioRxiv have been entering the market to provide faster access to unpublished results. Open peer review is practiced by ever more journals and consortia. Post- Publication Peer Review is a new buzz word to use crowd-sourcing to evaluate scientific research. Publication of research results is at the center of the scientific enterprise. It is therefore essential not only for young scientists to have a good overview of the changing publishing landscape. This seminar explores the ways in which the speed and network character of the internet breaks down old categories of scholarly publishing and creates new ways of communicating scientific results.

2014 Jun 13 10:30


The concept of the Jambogun was announced at the last Institute's Conference and the Internal Scientific Committee (ISC) has taken on the organization of this event.

The first round of speakers:

Silvia Adelhelm, Friedrich Anders, James Anderson,

Rainer Arlt, Metin Ata, Samuel Barden,

Olga Bellido Tirado, Abhijit Bendre, Irene Bernt,

Gabriel Bihain, Maria del Pilar Bonilla-Tobar, Joseph Caruana,

Gabriele Cescutti, Jose Chavez-Boggio, Cristina Chiappini,

Maria-Rosa Cioni, Claudia Conrad, Peter Creasey,

Andrea Diercke, Igor Di Varano, Katjana Ehrlich, Rene Eisermann.

You can download the talks here (pdf, 29 MB).

2014 Jun 06 10:30

Re'em Sari


Supernovae Shock breakout and Low Luminosity Gamma Ray Bursts

2014 May 27 11:00

Special Seminar: Richard de Grijs

(Kavli Institute for Astronomy and Astrophysics, Peking University)

Not-so-simple stellar populations in Local Group star clusters

Until about a decade ago, star clusters were considered "simple" stellar populations: all stars in a cluster were thought to have similar ages and the same metallicity. Only the individual stellar masses were thought to vary, in essence conforming to a "universal" initial mass function. Over the past decade, this situation has changed dramatically. Yet, at the same time, star clusters are among the brightest stellar population components and, as such, they are visible out to much greater distances than individual stars, even the brightest, so that understanding the intricacies of star cluster composition and their evolution is imperative for understanding stellar populations and the evolution of galaxies as a whole. I will discuss my group's recent progress in this context, with particular emphasis on the properties and importance of binary systems, the effects of rapid stellar rotation, and the presence of multiple populations in Local Group star clusters across the full age range.

2014 May 23 10:30

Torsten Boehm

(CNRS - Université de Toulouse)

Rotation, activity and stellar oscillations in Vega? - Illustrating the power of high resolution stellar spectroscopy and velocimetry

In a first part of my presentation I will show the power of asteroseismology based on high resolution spectroscopy, illustrated on quasi continuous spectroscopic time series of oscillating Herbig Ae stars. Some of these stars are pre-main sequence delta-Scuti pulsators and their strongly irregular frequency spectrum can only be understood by analyzing extensive spectrocopic data sets, enabling the determination of oscillation modes, fundamental stellar parameters as well as the dynamic behaviour of stellar activity tracers (eg. rotational modulation). In a second part will present velocimetric results at the m/s precision: the rapidly rotating standard Ae star Vega has been observed during 5 nights with the highly stabilized velocimeter/spectrograph Sophie at OHP/ France. New insights on stellar oscillations in that category of stars have been searched for and are presented. The detailed study of photospheric line variations enabled us to conclude on the stellar rotation period, providing a direct answer to a longlasting polemics between spectroscopists and interferometrists. I will finish the talk with a short presentation of the challenging Neo-Narval instrumental project, the radial veloicty stabilisation of the Narval/TBL spectropolarimeter.

2014 May 21 11:00

Special Seminar: Mark Siewert

(Argelander-Institut f. Astronomie Bonn)

IBEX, Voyager and the outer heliosphere

In the past decade, most of what we knew about the outer heliosphere has been put into doubt. Observations of outer heliospheric plasmas and magnetic fields by the IBEX and the Voyager missions demonstrated many nontrivial properties that until then had been absent from theoretical and numerical modeling. New models are currently being developed, aiming to describe the multicomponent solar wind termination shock, plasma flows in the inner and outer heliosheath, and also the heliopause.

I give an overview of the current state of the modeling progress, and present multiple aspects of the problem where current progress is still lacking. These aspects include the geometry and the boundary conditions of the inner heliosheath, i.e. the solar wind termination shock and the so-called heliocliff, which might consist of a nonideal heliopause.

2014 May 15 11:00

Special Seminar: Grzegorz Kowal

( )

Fast magnetic reconnection in turbulent media

In this talk I will present the results of our numerical studies on a model of fast magnetic reconnection in the presence of weak turbulence proposed by Lazarian and Vishniac (1999). The three-dimensional direct numerical simulations show that the reconnection of magnetic field becomes fast, i.e. independent of resistivity, in the presence of weak turbulence in the way consistent with the Lazarian and Vishniac (1999) model. I will discuss our results on the reconnection rate scalings, independence of the way of the turbulence injection happens, the ability of reconnection to generate turbulence and therefore self-sustains its fast rate, as well demonstrate that the process of reconnection is an efficient particle accelerator producing cosmic rays through the first order Fermi process.

2014 May 12

Rafael Rebolo

(Instituto de Astrofísica de Canarias, Tenerife, España)

Free-floating super-Jupiters: from star clusters to the solar neighbourhood

Free-floating objects with a few times the mass of Jupiter are known in star clusters since year 2000. Subsequent work on the substellar mass function of young star clusters showed that these objects are rather numerous, at least as numerous as main sequence solar-type stars. I will review imaging searches for these objects in sigma Orionis and in the Pleiades star clusters, as well as searches in the solar neighbourhood (including the latest discovery of a super Jupiter at about 2pc from the Sun). The photometric and spectroscopic caracterization of free-floating super-Jupiters is a major astrophysical challenge. In the solar neighbourhood they are expected to display very low atmospheric temperatures (below 300 K) and extremely low luminosities.

2014 May 09 10:30

Marica Valentini


The joint action of asteroseismology and spectroscopy of Red Giants in the characterization of the Galactic disk.

Nowadays big spectroscopic surveys are providing unique stellar databases for better investigation of the formation and evolution of our Galaxy. Great attention must be devoted to the accuracy of the basic stellar properties derived by pipelines adopted by these surveys: large uncertainties in stellar parameters lead to large uncertainties in abundances, distances and and ages. Solar-like oscillating red giants represent a useful set of stars for both testing pipelines and for investigating the Milky Way, thanks to the high precision of the seismic gravities (precision below ~0.05 dex) and the precision that can be reached in determining distances and ages.

In order to implement the use of seismic observables in the process of spectroscopic analysis, I developed an automated tool for measuring atmospheric parameters (Teff ,log (g), [Fe/H]) for F-G-K dwarf and giant stars. The tool, when seismic data are available, performs the spectral analysis of Red Giants by fixing the surface gravity to th accurate value provided by asteroseismology.

In this seminar I will also show preliminary results on the use of CoRoT Red Giants in the characterization of the Milky way disk and in testing the accuracy of pipelines in the frame of the CoRoT-Gaia-ESO survey collaboration.

2014 May 07 11:00 Special Seminar: Ralph Neuhäuser

(Astrophysikalisches Institut und Universitäts-Sternwarte Jena)

The C-14 event in AD 774/5 - supernova, gamma-ray burst or solar activity?

2014 May 05

Pavol Schwartz

Astronomical Institute of the Slovak Academy of Sciences

Non-LTE modelling of the prominence fine structure using hydrogen Lyman line profiles

A prominence on NW limb was observed on 18 May 2005 in several EUV spectral lines and in whole hydrogen Lyman series (including Lyman alpha) by the CDS and SUMER spectrographs, respectively, both on board of the SOHO satellite. From Earth the prominence was observed by the National Solar Telescope in the H_alpha center. The prominence looks in H_alpha as two radially directed columns while in EUV transition-region spectral lines OV 629 A and NeVI 562 A we can see in emission both these two structures and material between them. Emission in these two lines, which temperatures of formation are 250000 and 400000 K, respectively, indicates presence of such rather hot plasma in prominence except of cool plasma (temperatures from approximately 10000 up to several ten thousands K) emitting in H_alpha and hydrogen Lyman lines. In the HeI 591 A the both H_alpha structures are seen in absorption in bright background. That indicates that the H_alpha structures contain very dense and cool plasma that emits less radiation in the HeI line than hotter and less dense plasma in between the two structures. The active part of the SUMER slit is crossing Northern one of the two H_alpha structures and partly area between them. Observations of SUMER were made with static slit and 18 observations of Ly_alpha and 36 observations of the higher Lyman lines were made. This large set of observed profiles of Ly_alpha -- Lyman_delta was statistically compared with synthetic profiles obtained using the multi-thread model with identical threads approximated by 2D horizontal slabs embedded in horizontal dipped magnetic field and irradiated from the chromosphere at their sides. The following four characteristics of profiles were used for statistical comparison: integral intensities, Lyman decrements -- ratios of integral intensities of individual Lyman lines and Lyman_beta, two-peaked profile asymmetries and ratio of intensities at profile central reversals and peaks. The multi-thread model with hotter outer threads was also tested and it was found: Temperatures in interior of the outer thread can be only slightly higher (several thousand K) that in internal threads. But still a prominence can have a hotter shell which radiates in transition-region lines such as OV 629 A and NeVI 562 A. Each thread has its own prominence-to-coronal transition region with an increase of temperature which is much steeper across than along magnetic field.

2014 Apr 11

Helene Courtois

University of Lyon France and University of Hawaii USA

Cosmic Flows give CLUES as to where is the dark matter in the Universe

While massive amounts of observational data as well as high performance super-computing capacities are becoming the norm for cutting edge research, our knowledge of the matter distribution in the Universe (on the Million Light years scale) remains an open question.

The science of mapping the heavens has since antiquity been known as "cosmography". On earth, cartographers evolved from surface mapping (2D) to elevation maps (3D) to tectonic mapping with real-time motions (GPS). Cosmologists are just now making this last step. In 2013 a detailed cartography of galaxy motions in a volume reaching 1% of the observable universe was made public, thanks to the joint efforts of two international projects: CLUES and "Cosmic Flows".

We have recently produced a newest catalog of galaxy gravitational velocities: "Cosmic Flows-2", which approximately doubles the dynamically cartographied volume of the universe. I will present results obtained when this catalogue is used by the CLUES project: an endeavor to run cosmological numerical simulations that are constrained to reproduce the observed cosmography. The time evolution of these simulations provides a detailed window on the history of how the local universe assembled and formed. I will conclude by focusing on a special place : the Great Attractor - a gravitational sink in the local universe which is pulling towards it many galaxies (including us). A comparison between the dynamics in the observed universe and the simulated one, allows us to map the dark matter distribution and to test the standard theory of structure formation. Mapping the distribution and motions of galaxies attempts to answer some of the most basic questions in cosmology: where are we? where do we come from? where are we going? and "why" are we going there?

2014 Apr 09

Special Seminar: Marie Martig

MPIA, Heidelberg

Formation histories of spiral galaxies

How do spiral galaxies form? what is the relative importance of mergers, gas accretion and internal instabilities for the formation of the bulge, thin and thick disk? and can we find signatures of these formation mechanisms in present day properties of nearby galaxies and in the Milky Way? I will present a suite of 33 cosmological re-simulations following the formation and evolution of Milky Way-mass isolated galaxies from z = 5 to 0. I will first discuss how the properties of bulges are related to the merger and gas accretion histories of their host galaxies, but will also show that the fine structure of galactic disks is the most sensitive indicator of past mergers.

2014 Apr 08 11:00

Special Seminar: Alex Markowitz

Univ. of California, San Diego; Karl Remeis Sternwarte & ECAP

First X-ray-Based Statistical Tests for Clumpy-Torus Models: Eclipse Events from X-ray Monitoring of Seyfert AGN

We present an analysis of multi-timescale variability in line-of-sight X-ray absorbing gas as a function of optical classification in a large sample of Seyfert AGN to derive the first X-ray statistical constraints for clumpy-torus models. We systematically search for discrete absorption events in the vast archive of Rossi X-ray Timing Explorer monitoring of 55 nearby type Is and Compton-thin type IIs.

We detect 12 eclipse events in 8 objects, roughly tripling the number previously published from this archive. Event durations span hours to years. The column density profile for an eclipsing cloud in NGC 3783 is doubly spiked, possibly indicating a cloud that is being tidally sheared.

We infer the clouds' distances from the black hole to span \sim 0.3 - 140 \times 10^4 R_g. In seven objects, the clouds' distances are commensurate with the outermost portions of the BLR, or the inner regions of infrared-emitting dusty tori. We discuss implications for cloud distributions in the context of clumpy-torus models.

2014 Apr 04

Matthias Mallonn


Spectroscopic characterization of extrasolar planets

About 20 years after the first discovery of planets orbiting other stars than the sun, the big topic now in the field changed from "Are they there?" to "What are they like?". The recent years saw a tremendous progress in exoplanet charaterization in terms of observing techniques and number of characterized planets, which allow now for comparative studies.

I am going to review the current status of exoplanet characterization by spectroscopy and tell about my own contributions to the field.

2014 Mar 28

Umberto Maio


Exploring the Cosmic Dawn

We investigate the birth and formation of primordial structures at early times via 3D numerical N-body, hydro, chemistry simulations including gas cooling, star formation, feedback effects and stellar evolution for stars with different masses and according to corresponding metal yields and lifetimes. This allows us to address physical and luminous properties of primordial stars and galaxies; the interplay between matter and radiation on cosmological scales; and the back-reaction of primordial stellar populations on the surrounding medium. Comparisons with current data of primordial cosmic observables, like gamma-ray-burst hosts, Lyman-alpha emitters and damped Lyman-alpha systems are finally proposed.

2014 Mar 21

Ansgar Reiners


Advances at the cool end of the Main Sequence: Dynamos and Exo-Earths

Astrophysics at the cool end of the Main Sequence experienced a strong push from the realization that low-mass stars are optimal targets for the search for Earth-like exoplanets. Today, several instruments are under construction or planned with the aim to search for planets around very cool stars. These instruments will open a new window into cool star physics and provide crucial information on stellar activity and the solar dynamo.

I will summarize recent observational results for stellar dynamos and some plans for instrumentation for the quest for Exo-Earths.

2014 Mar 14

Eiichiro Komatsu


Critical Tests of Theory of the Early Universe using the Cosmic Microwave Background

The Cosmic Microwave Background (CMB), the fossil light of the Big Bang, is the oldest light that one can ever hope to observe in our Universe. The CMB provides us with a direct image of the Universe when it was still an "infant" - 380,000 years old - and has enabled us to obtain a wealth of cosmological information, such as the composition, age, geometry, and history of the Universe. Yet, can we go further and learn about the primordial universe, when it was much younger than 380,000 years old, perhaps as young as a tiny fraction of a second? If so, this gives us a hope to test competing theories about the origin of the Universe at ultra high energies. In this talk I present the final results from nine years of observations using the Wilkinson Microwave Anisotropy Probe (WMAP) satellite, and discuss future prospects on our quest to probe the physical condition of the very early Universe.

More information about this event.

2014 Mar 13 14:00

Special Seminar: Alejandro Benítez Llambay

IATE Córdoba

Imprint of Reionization on the Star Formation Histories of Dwarf Galaxies

We use one of the CLUES cosmological hydrodynamical simulation to explore the impact of cosmic reionization on the star formation history (SFH) of isolated dwarf galaxies. We focus our analysis on dwarfs that form in halos with virial mass between 3x10^9 and 2x10^10 solar masses at redshift z = 0. These galaxies exhibit, as do nearby dwarfs, a wide diversity of star formation histories. From ancient systems that have completed their star formation ~10 Gyr ago to young dwarfs that form most of their stars in the past ~5 Gyr. Overall, star formation declines at intermediate times (4 < t/Gyr < 8), a feature that it is also strikingly clear in the average star formation history of nearby dwarfs. We trace this feature to the impact of cosmic reionization.

2014 Feb 28 10:30

Mercedes Richards

Penn State, USA

3D Images of Astrophysical Gas Flows in Interacting Binary Star Systems

Interacting binary star systems are in the process of mass transfer during which gas will flow along a path called the gas stream, from the more evolved mass-losing star to its companion. Images of these gas flows have not yet been realized with direct-imaging techniques because such details cannot be resolved even with the largest telescopes. However, the image reconstruction technique of Doppler tomography has revealed 2D images of gas flowing along the predicted gravitational path between the stars, accretion disks or accretion annuli around the mass-gaining star, hot spots where the gas flow collides with the surface of the star, and evidence of magnetic flows connected with the cool magnetically-active mass-losing star. The extension to 3D tomography has unveiled views of extensive gas flows beyond the central plane of the binary system. These new 3D images show that the magnetic field of the mass losing star can influence the gas motions dramatically in some cases. Hence, tomography has revealed the active environments that exist in a range of objects from direct-impact binaries to cataclysmic variables and gamma ray binaries.

2014 Feb 21 10:30

Pavel Kroupa


The vast polar structures around the Milky Way and Andromeda, and the implications thereof for fundamental physics

The current cosmological model rests on Einstein's theory of general relativity. In order for it to be consistent with large-scale structure data, the existence of cosmologically relevant physical processes need to be postulated: inflation, cold or warm dark matter particles and dark energy. Each of these is not well understood, but assuming the resulting standard mathematical description is a representation of cosmological reality, this representation can be tested in a different regime, namely on the scales of the Local Volume of galaxies down to individual galaxies. It is found that each test which has been designed shows the standard description to fail such that the currently standard model of cosmology is difficult to be upheld. In particular, the Dual-Dwarf-Galaxy Theorem, which must be true in the standard model, is falsified. The arrangement of satellite galaxies in rotating disk-like vast near-polar structures around both, the Milky Way and Andromeda, support this conclusion. As suggested by Milgrom, scale-invariant dynamics may be showing a new direction for the understanding of the astrophysics of galaxies.

2014 Feb 20 11:00

Special Seminar: Will Saunders

Australian Astronomical Observatory (AAO)

AESOP and the AAO Instrumentation Program: Technology for large scale surveys

Survey astronomy has been driven for decades by the dramatic improvements in signal-to-noise and multiplex capability afforded by rapidly evolving technology, at a combined rate of about a factor ten per decade. Each generation of instrument brings new challenges in achieving these gains within fixed cost envelopes. The AAO has always maintained a very high profile in this area, with the UKST and AAT being virtually dedicated to this work. We have also delivered instruments to Subaru and ESO, and are currently designing instruments with Gemini, LBNL, GMT and AIP, as well as new survey instruments for our own telescopes. I will review the AAO instrumentation program, especially focussing on AESOP, the positioner for the 4MOST facility. I will also cover Wide Field Corrector and spectrograph designs, IFU technology, and OH suppression.

2014 Feb 14 10:30

Maria-Rosa Cioni


Status of the VMC survey and Proper Motion of the Magellanic Clouds

The VISTA near-infrared YJKs ESO public survey of the Magellanic Clouds system (VMC) began observations in 2009. To date the survey is about 50% complete and several results have already been obtained. These studies confirm the superior quality of the data to meet the main objectives of deriving spatially resolved star formation histories and the 3D structure of the system, and to contribute to a wealth of legacy science studies.

In this presentation I will briefly review the status of the VMC survey and then I will focus on measurements of the proper motion of stellar populations across the Magellanic system. This is achieved by comparing both the VMC data with the 2MASS data or by using VMC data alone for different, by age, stars selected from colour-magnitude diagrams. The implications of this study on the evolution of the Magellanic system will also be discussed.

2014 Feb 07 10:30

Christoph Kuckein


Near-infrared spectropolarimetry of solar filaments

Solar filaments form as elongated structures of dense plasma above magnetic polarity inversion lines. They appear as absorption features on the solar disk and in emission above the solar limb, where they are called prominences. On-disk filaments are conspicuous in the quiet Sun (quiescent filaments) and in active regions (active region filaments) when observed in strong chromospheric absorption lines, e.g., in the He I 1083 nm multiplet and the H-alpha 656.3 nm line. I will review the major properties and formation models of filaments, concentrating on active region filaments. I will introduce near-infrared spectropolarimetric observations in the He I 1083 nm spectral range acquired with the Vacuum Tower Telescope at Observatorio del Teide, Tenerife, Spain. In a comparative study, I analyze full Stokes spectra of the Si I 1082.7 nm line and the He I 1083 nm triplet by using three different inversion codes. Finally, I will discuss the infered vector magnetic field in the context of standard filament formation models.

2014 Jan 31 10:30

James Binney


Extracting Science from Surveys of our Galaxy

Our Galaxy offers a unique opportunity to establish the correctness or otherwise of the LCDM cosmology. Massive surveys are underway, culminating in the Gaia mission. Equilibrium dynamical models will play a key role in extracting science from these surveys. We have been developing new types of models and fitting them to available surveys, most recently the RAVE survey for which Matthias Steinmetz in the PI. The status of this work will be reviewed, especially its current focus: weighing our Galaxy's disc(s).

2014 Jan 24 10:30

Emre Isik


Modelling magnetic flux transport in the Sun and active cool stars

I present an overview of the physical processes thought to underly the observed cyclic magnetic field of the Sun. The turbulent solar convection zone leads to a diversity of effects, which are responsible for the self-organisation of magnetic fields and large-scale flows. I summarise the successes and drawbacks of surface flux transport models, dynamical thin flux tube models, and Babcock-Leighton-type flux transport dynamos, in comparison with observational results. I finish the presentation by discussing our understanding of large-scale magnetism in stars more active than the Sun.

2014 Jan 20 11:00

Special Seminar: Sasha Kashlinsky

NASA Goddard Space Flight Center

Probing the cosmic infrared background from first stars with gamma-ray absorption at high z

I will discuss the evidence for significant emissions from first stars and black holes era present in recent cosmic infrared background (CIB) measurements. A consequence of this high redshift CIB component is that there should be a large density of CIB photons which is conserved (in comoving coordinates) from the epoch of emissions. These photons would then be the dominant opacity sources due to two photon absorption with high-energy gamma-ray emitters at sufficiently large z. After robustly reconstructing the floor to this opacity from known sources, the excess absorption is measurable with Fermi/LAT data, and would provide important information on the first stars era. I will discuss the prospects and the region of measurability of this feature in the upcoming Fermi/LAT data.

2014 Jan 17 10:30

Andrea Kunder


Galactic Bulge Kinematics from the Bulge Radial Velocity Assay (BRAVA)

Only for stars in the Milky Way is it currently possible to examine both the three dimensional kinematics and composition of a central bulge/bar population, offering a unique laboratory for the study of galaxy formation and evolution. I will present new results from the BRAVA spectroscopic survey of giants in the Galactic bulge, and highlight how this database constrains dynamical models of the Galactic bulge and the formation of the Milky Way Galaxy.

2014 Jan 10

Alexander Warmuth


Constraining energy release and particle acceleration in solar (and stellar) flares with hard X-ray observations

In solar flares, stored magnetic energy is impulsively converted to kinetic energy of nonthermal particles and bulk mass motions, and to thermal energy of hot plasmas. Both nonthermal particles and thermal plasmas generate signatures in the hard X-ray range. NASA's RHESSI mission allows us for the first time to quantitatively characterize both thermal and nonthermal particle populations, and thus to put strong constraints on energy release and particle acceleration processes. I will review some of the most important results of the RHESSI mission and discuss some recent work on energy partition in solar flares. Possible implications of these studies for stellar flares will be discussed. Finally, the upcoming Solar Orbiter mission will be introduced.

2013 Dec 17

Special Seminar: Areg Mickaelian Byurakan

Astrophysical Observatory (BAO), Armenia

Multiwavelength Properties of Active Galaxies

A review of recent multiwavelength (MW) studies of active galaxies will be given. The activity types of 779 Markarian galaxies have been revised based on available SDSS spectra and a MW catalogue of Markarian galaxies has been created. Such MW catalogue is being created for all bright (m<17) AGN as well, which will include their gamma-ray, X-ray, UV, optical, IR and radio data, altogether 38 photometric measurements, giving a large possibility for comparative studies of their SEDs. Activity types for 83 Byurakan-IRAS Galaxies (BIG) have been determined from SDSS DR7-DR9. We have cross-correlated X-ray (ROSAT) and radio (NVSS, FIRST) catalogues and obtained a sample of high probability bright AGN (Blazars, QSOs, Seyferts), which will be observed for spectroscopic identification. On the other hand, we have cross-correlated NVSS and FIRST and obtained a sample of variable radio sources (having > 3 sigma deviations between the two catalogues), as well as investigated the radio structure of the NVSS sources having multiple associations in FIRST (central source, radio lobes and possible jets).

2013 Dec 17

Special Seminar: Else Starkenburg

University of Victoria, Canada

Galactic archaeology to its limits - Understanding the most pristine stars

The lowest metallicity stars that still exist today probably carry the imprint of very few supernova. As such, they represent our best observational approach to understanding of the First Stars. Within the most metal-poor stars, various chemical sub-classes are found. The intriguing question therefore is if these chemical anomalies teach us something about the very first stages of star formation? I will review our understanding of the origin for the peculiar abundance patterns in various chemical subclasses of these pristine stars, taking into account new observational data from monitoring programs.

2013 Dec 16

Special Seminar: Andreas Faltenbacher

University of the Witwatersrand, Johannesburg

Modelling the HI Correlation Function - an Abundance Matching Approach

With SKA and the precursor Instruments (MeerKat and ASCAP) the number of HI detected galaxies will increase substantially. In order to use this data for cosmology it is important to connect the galaxies with the background dark matter density field. I discuss an abundance matching approach which applies similar techniques to the HI as introduced for the stellar component of galaxies.

2013 Dec 10

Special Seminar: Radek Wojtak

Phase-space shapes of the virialised cosmic structures

It is a well-known fact that dark matter (DM) haloes and galaxy groups embedded within have aspherical shapes approximated by preferentially prolate triaxial ellipsoids. On the other hand, the shapes of these objects in velocity space are commonly assumed to be spherical. In the first part of my talk, I will show that this assumption cannot be reconciled with the actual velocity distributions of DM particles in simulated haloes, which exhibit strong axial symmetry, with the degree of this symmetry increasing towards the halo centre. I will discuss how this assumption affects most measurements of the velocity anisotropy in simulated haloes. In the second part of my talk, I will present the first observational constraints on the phase-space shapes (shapes in both position and velocity space) of clusters and rich groups from the SDSS. I will compare these results with cosmological simulations and draw conclusions on considerable limitations of spherically symmetric dynamical models.

2013 Dec 06

Achim Brauer

GFZ Potsdam

The influence of the Sun on Earth’s climate: what can we learn from lake mud?

This presentation discusses effects of solar activity variations on climate from a geological point of view. After a brief overview including reports of solar signals in geological archives, an introduction to seasonal lake sediment formation and modern analytical methods for high resolution climate reconstruction will be given. On the basis of two examples from the mid-latitudes, possible amplification mechanisms of solar-climate links will be discussed. The first example is from Lake Meerfelder Maar, a volcanic lake in the Eifel (Western Germany), where the effects of the Homeric Grand Solar Minimum ca 2700 years ago can be clearly demonstrated, and in the second example, a 5500 flood record from Lake Ammersee (Southern Germany) is shown and the relation of these data to long-term reconstructions of sun activity will be discussed.

More information about this event…

2013 Nov 29

Jorge Federico Gonzalez

Conicet, Argentina

The role of stellar multiplicity for the development of chemical anomalies in HgMn stars

In recent years HgMn stars have attracted attention after the discovery, in several of them, of surface chemical spots of different elements. In this talk I will review recent observational results concerning the binarity and multiplicity of HgMn stars, with emphasis on the chemical spot patterns in binary systems and on the nature of their binary companions. The system HD161701, recently discovered as the first binary containing a HgMn primary and a classical magnetic Ap companion will be described in some detail.

2013 Nov 25

Special Seminar: Joar Brynnel

University of Arizona

LBT Status and Developments

For the LBTO, the second half of 2013 is filled with an unprecedented number of instrument arrivals to the LBT Observatory on Mt. Graham. Current status of the Observatory will be presented together with an update of ongoing commissioning projects, along with an outlook into the future planning.

2013 Nov 22

Jeremy Walsh


NGC 5128 as a nearby template for the star formation history in early-type galaxies

NGC 5128, the elliptical galaxy underlying the Centaurus-A radio source, is the nearest example of a large early-type galaxy, despite its prominent dust lane. This proximity makes it ideal for a variety of investigations of the present-day structure and history of interactions in an early-type galaxy. Some studies of the planetary nebulae (PNe), sampling the late stages of evolution of the common, low mass, stars, are described. Many PNe have been detected in NGC 5128, abundances of the light elements have been determined from spectra and velocities measured to study the local and global kinematics. The contribution of these results to the star formation history will be outlined.

2013 Nov 21

Special Seminar: Jan-Pieter Paardkooper

MPE Garching

The sources of cosmic reionisation

The formation of the first stars and galaxies marks the beginning of the Epoch of Reionisation, when the inter-galactic gas was transformed from cold and neutral to a hot, ionised plasma. The coming years promise to be very exciting for the study of reionisation as newly build low-frequency radio arrays like LOFAR will likely detect the 21 cm signal of neutral hydrogen during this important epoch. For the interpretation of this signal numerical simulations are vital but these are extremely challenging due to the large simulation volumes that are required. These simulations therefore rely heavily on the source models used. My work aims to test these assumptions by simulating the sources of reionisation at high resolution taking into account the relevant baryonic processes. Using high-resolution simulations of isolated galaxies and a large sample of galaxies from cosmological galaxy formation simulations I will show which physical processes drive the escape of ionising photons from galaxies and how this depends on the properties of the halo in which galaxies are forming. Our simulations show that the source models in large-scale reionisation simulations are inaccurate and that reionisation is likely to progress markedly different from what simulations have shown so far.

2013 Nov 20

Special Seminar: Edward Macaulay

University of Oxford

Surprising Results from Peculiar Velocities

Peculiar velocities offer a unique window on the dark universe. At low redshift, velocities can be directly measured with luminosity distances, and at high redshift, the velocity field can be inferred indirectly via Redshift Space Distortions. In this talk, I will present results from both methods, which can both appear in tension with LCDM. At low redshift, bulk flows suggest a large scale excess in the matter power spectrum, while at high redshift, RSDs consistently measure a growth rate less than LCDM with Planck parameters. At face value, the RSD results may be evidence of modifications to gravity beyond General Relativity, although there is also independent evidence that systematic effects in the data have not been fully accounted for. I will highlight possible systematic effects and physical explanations for these results, although the current tension between Planck and RSDs remains a mystery. In light of this, I will demonstrate how the tension from bulk flows is dramatically reduced as a more complete picture of the velocity field is considered, and suggest possible directions for future surveys.

2013 Nov 18

Special Seminar: Areg Mickaelian

Byurakan Astrophysical Observatory (BAO), Armenia

Search and Studies of Active Galaxies in the Byurakan Astrophysical Observatory

The Byurakan Astrophysical Observatory traditionally is involved in search and studies of active galaxies. Viktor Ambartsumian was the first in mid-1950s to pay attention to the phenomenon of the activity of galactic nuclei. Markarian survey was in fact the first systematic survey for AGN and it also resulted in definition of Starbursts (SB). Arakelian and Kazarian galaxies and Shahbazian groups are known as well. Markarian survey was also used for search and study of blue stellar objects, including QSOs and Seyferts, as well as for optical identification of IR sources. Later on, in collaboration with Hamburg Observatory, optical identification of ROSAT sources was carried out and the largest sample of X-ray selected AGN was created. For Markarian galaxies, a multiwavelength catalogue has been created and activity types have been revised. We have created the Digitized First Byurakan Survey (DFBS), the digitized version of Markarian survey, having some 40 million low-dispersion spectra of 20 million objects.

2013 Nov 15

Davor Krajnovic


ATLAS3D Project: what shapes early-type galaxies?

ATLAS3D project is a multi-wavelength survey of a complete and volume limited sample of morphologically selected early-type galaxies. 260 galaxies not exhibiting spiral arms or extended dust lanes were extracted from a complete parent sample of 871 galaxies brighter than -21.5 mag (K-band) and observed from La Palma with the SAURON integral-field spectrograph mounted on the 4.2 William Herschel Telescope. Additionally, the majority of sample galaxies were observed also with the IRAM 30m telescope, CARMA and Westerbork interferometeric arrays, as well as the MegCam at the Canada-France-Hawaii-Telescope.

In this talk I will briefly describe the survey and discuss the clues for formation and evolution of early-type galaxies based on structure, kinematics and dynamics of observed galaxies, as well as their stellar populations and properties of gas in the cold, warm and hot phases. The main conclusions are that nearby early-type galaxies carry imprints of various types of formations processes (dissipative, non-dissipative, in-situ, ex-situ, environmental effects), most evident at non edge-on views of the fundamental (mass) plane, that velocity dispersion is the best predictor of galaxy properties and that spirals and early-type galaxies should be considered together, as they form a parallel and a continuous sequence in their properties.

2013 Nov 01

Joseph Caruana


The search for the most distant galaxies in the Universe

Recent years have seen a concerted effort at pushing observations of galaxies to ever higher redshifts. The advent of Wide Field Camera 3 (WFC3) on the Hubble Space Telescope opened up new doors for the pursuit of extremely high redshift galaxies, with several groups making use of the Lyman-break technique to identify high-z candidates. However, while the number of selected candidate galaxies at z > 6.5 is substantial, the number of spectroscopically confirmed objects (via follow-up observations aimed to detect Lyman-alpha emission in these objects) remains very small. In this talk I will review the progress made in the field and will also comment about the very difficult challenges and some of the pitfalls associated with this endeavour, which from time to time have led to conflicting results.

Later in the talk I will focus the attention on the use of Lyman-alpha emitting galaxies as a cosmological tool to probe the neutral fraction of Hydrogen in the universe and to investigate the era of reionization. Current observations seem to suggest that there is a drop in the number of Lyman-alpha emitters at z > 7 when compared to lower redshifts. The possible meanings of this apparent number drop will be discussed.

2013 Oct 29

Special Seminar: Alexei Moiseev

Special Astrophysical Observatory, N. Arkhyz, Russia

Scanning Fabry-Perot interferometer at the SAO RAS 6-m telescope: current state and results

The scanning Fabry-Perot interferometer is a powerful tool for 3D spectroscopic study of the emission-line kinematics of extended objects. I briefly review the opportunities of this technique on the last decade observations at the SAO RAS 6-m telescope. The results concerning different Galactic and extragalactic objects are considered: Herbig-Haro flows, polar and collisional rings galaxies, expanding bubbles in dwarf galaxies and a hypernova remnant.

2013 Oct 22

Special Seminar: Timo Reinhold


Rotation and differential rotation of stars in the Kepler field

The talk is about the results from high-prescision photometry with the Kepler satellite of an extremely large sample of stars.

2013 Oct 18

Special Seminar: Stuart Barnes

The search for extrasolar planets using high resolution echelle spectroscopy

An overview of the design and construction of high resolution echelle spectrographs designed for precision radial velocity observations of extra-solar planets.

2013 Oct 01

Special Seminar: Gilles Rasigade

Silicon Photonics: 40Gbit/s integrated optical modulator

The silicon photonics has emerged as the key area of research for optical telecommunications with the objective of developing an integrated transceiver fully-compatible with the available CMOS technology. In this context, developing an optical modulator available for 40Gbit/s applications can be seen as the cornerstone of the research in this domain. The presentation will present the design of such components, fabrication process-flow and characterization.

2013 Sep 30

Aaron Geller

Northwestern University, USA

The Dynamical Environments of Open Star Clusters

Most stars are born in star clusters. However, star clusters can be hostile environments, where close stellar encounters can be frequent and can have violent consequences, including direct stellar collisions. Such encounters can dramatically alter stellar and planetary systems, and can produce exotic stars that define new pathways in stellar evolution. Open clusters are particularly valuable to our understanding of these processes due to their accessibility to both comprehensive ground-based observations and full-scale sophisticated N-body simulations. Indeed, the combination of both our observations and N-body simulations is beginning to reveal a highly accurate and detailed picture of the stellar dynamical environment of open clusters. In this talk, I will discuss the impact of these dynamical processes on the observed characteristics of binary stars and planetary systems, and the origins of X-ray sources and blue straggler stars.

2013 Sep 27

Special Seminar: Till Sawala

Durham University, England

Structure formation: not just dark matter

While collisionless simulations of cold dark matter (CDM) successfully describe the large scale evolution of structures, its apparent failures on small scales have prompted renewed interest into alternative models. I will review the principle challenges to CDM, and discuss some of the proposed solutions. Based on a comparison of numerical simulations with and without baryons, I will also discuss the impact of baryons on structure formation, and show that gas pressure, re-ionisation, supernova feedback, and truncated accretion systematically reduce the total masses and abundances of structures. In particular, I will show that accounting for the reduced mass of haloes, and for the presence of unobservable "dark" haloes, largely reconciles the CDM predictions with the observations.

2013 Sep 27

Sam Barden

National Solar Observatory, USA

Polarimetric Spectroscopic Imager (PSI) - a new approach to observing the heavens

Volume Phase Holographic Gratings (VPHGs) have a unique characteristic when the light is diffraction from the incoming beam by a right angle where only one polarization state is diffracted with nearly 100% efficiency while the other polarization state is passed through undiffracted. This allows an innovative instrument design of a high resolution spectro-polarimeter with very high efficiency at quite high spectral dispersion but with a compact and simple implementation. I will present the design concept, expected performance levels for a variety of telescope implementations, and review many of the potential applications that it offers for astronomy.

2013 Sep 20

Isabel Suarez


Searching for the missing baryons in the Warm-Hot Intergalagtic Medium

The so called Warm-Hot Intergalactic Medium (WHIM) is considered as one of the biggest reservoirs of baryons in the universe. These structures consist of shock-heated gas with temperatures in the range 10^5-10^7 K and overdensities δ < 100. This combination of high temperatures and small densities make the WHIM very difficult to detect. However, being highly ionized the hot electron gas within the WHIM, which interact with the CMB photons, could leave an imprint in the CMB power spectrum of anisotropies by means of the Sunyaev-Zeldovich effect (SZ). Modelling the WHIM, one can give an estimate of the amplitude of this anisotropies. In this talk I will describe how to model the WHIM in order to calculate the SZ signal induced by the warm-hot gas. Then, I will discuss the possibility of finding this signal in WMAP/Planck data together with a parameter study using WMAP/SPT data.

2013 Sep 06

Gabriele Cescutti


The First Stars: chemical signatures in the Milky Way

Soon after the Big Bang, the appearance of the first stellar generations drastically changed the course of the history of the Universe by enriching the primordial gas with elements heavier than helium through both stellar winds and supernova explosions. High-resolution hydrodynamical simulations of the formation of the First Stars suggest that these objects have played a key role in the formation of the first galaxies. The only way to currently validate the picture arising from the most modern hydro-dynamical simulations of the formation of First Stars is to search for their imprints left on the oldest stars in our Galaxy. The observed chemical signatures coupled with chemical evolution models, can provide new insights to check the validity of the theoretical predictions of stellar formation in the early Universe. In the last years our group has found that many chemical anomalies observed in very metal-poor halo stars, suggest the first stellar generations to have been fast rotators; similar findings can be also extended to the old population of the Galactic bulge.

2013 Aug 21

Special Seminar: Joseph F. Hennawi

Max-Planck-Institute for Astronomy, Heidelberg

Probing the Circumgalactic Medium in Absorption and Emission

2013 Jul 10

Special Seminar: Nicolas Tejos

Durham University, England

On the connection between the IGM and galaxies at z<1

I will present observational results on the large-scale connection between the intergalactic medium (IGM) and galaxies at z<1. I will focus on a statistical approach to this problem by measuring the gas-galaxy 2-point cross-correlation, and comparing it with both the galaxy-galaxy and the gas-gas auto-correlations, as a function of different absorber/galaxy properties. These results come from one of the largest samples of HI absorption lines and galaxies in the same volume obtained from deep spectroscopic galaxy surveys (VLT/VIMOS, Gemini/GMOS, Keck/DEIMOS) around QSOs having high resolution UV spectroscopy (HST/COS, HST/FOS). I will also present results from a complementary study on HI absorption systems found within and around galaxy voids at z<0.1.

2013 Jul 10

Special Seminar: Nikolaos Fanidakis

MPA Heidelberg

The halo environment of AGN: predictions from semi-analytics

AGN inhabit a wide range of dark-matter halo environments; from the centres of clusters, where radio galaxies reside, to average Milky-Way like haloes in which quasars are found. In my talk, I will demonstrate that the variety of AGN environments can be explained when more than one accretion modes are responsible for fuelling the growth of black holes. I will show this by means of a model which combines N-body simulations and analytical prescriptions in a Λ cold dark matter universe. With this model, I will explain how the large scale environment of AGN depends on luminosity, AGN type and black hole mass. I will further demonstrate how AGN can be used, along with line-emitting galaxies, to pinpoint the location of galaxy protoclusters in the high-redshift Universe.

2013 Jul 03

Special Seminar: Nelson Padilla

Pontificia Univ. Cat. de Chile, Santiago

Effects of stochasticity of acquisition of angular momentum in the evolution of galaxies

Dark matter (DM) haloes, the cradles where galaxies form and evolve, acquire angular momentum in a stochastic way which results in a final non-zero DM adimensional spin parameter. We will see how this process translates into the ability of the galaxy, living in this DM halo, to form stars. To do this we will first measure this stochasticity from the Millennium II simulation, and then see how it affects the properties of the disc of baryons that forms in the center of a DM halo. We will see that the smooth infall of matter comes in chunks with almost, but not quite, random angular momenta, which affects the ability of a disc to form stars and also the frequency of instabilities in the disc leading to the formation of bars and pseudo-bulges, constituting an episodic disc creation.

2013 Jul 03

Special Seminar: Jens Lautenbach

Leibniz-Institute of Atmospheric Physics, Kühlungsborn, Germany

Lidar measurements in the atmosphere

This presentation is about the application of ground based Rayleigh and resonance lidar mea- surements in altitudes from 30 up to 105 km. Technical aspects of those systems and parti- cular filter techniques to achieve daylight capability will be discussed. The Leibniz-Institute of Atmospheric Physics is operating three daylight capable lidar. The importance of daylight measurements for the understanding of our atmosphere will be shown with the help of selected examples.

2013 Jun 21

Daniel Zucker

Macquarie University, Sydney, Australia

GALAH takes flight

The GALAH (GALactic Archaeology with HERMES) Survey is a major Australian-led project to obtain detailed elemental abundances for over a million stars, and apply the technique of chemical tagging -- identifying chemically similar groups of stars in the Galactic disk, which presumably formed together -- to decipher the star formation, migration and minor-merger history of the Milky Way. HERMES, scheduled for commissioning in late 2013, is a multi-fibre spectrograph being built for the AAT 3.9m telescope at Siding Spring, designed to simultaneously obtain high resolution (R ~28000 or ~45000) spectra for ~400 stars over a 2° field of view. For the GALAH Survey, ~106 stars (down to V~14, at a S/N of ~100 per resolution element) will be observed in four passbands selected to include elements from all major independently-varying element groups. Providing chemical abundances and precision radial velocities, GALAH will be directly complementary to the astrometry, parallaxes and proper motions which will come from ESA's Gaia mission.

2013 Jun 14

Simon White

MPA Garching

Cosmological results from the Planck satellite

ESA's Planck mission is the third generation satellite to study the Cosmic Microwave Background. It has mapped the full sky at nine frequencies spanning a factor of 30 in wavelength with a resolution and sensitivity superior to those of any previous experiment. Results from the nominal 15.5 month mission were released in a set of 28 papers on 21 March 2013. I will present the maps together with highlights of the cosmological results derived from them. These include: (i) the most precise measurements so far of the parameters describing the content and structure of our Universe, (ii) constraints on the physics driving its very early evolution, (iii) some anomalies which may indicate physics beyond our current standard model, and (iv) maps of the distributions of total mass, of baryonic mass and of star-formation in galaxies throughout the entire visible unverse in front of the CMB.

You can download the talk here (pdf, 17 MB).

2013 Jun 13

Special Seminar: Julio F. Navarro

University of Victoria

Dwarf Galaxies as Cosmological Probes

A prime challenge to our understanding of galaxy formation concerns the scarcity of dwarf galaxies compared with the numerous low-mass halos expected in the current ΛCDM paradigm. This is usually accounted for by assuming that energetic feedback from evolving stars confines dwarf galaxy formation to relatively massive halos spanning a narrow mass range. I will highlight a number of observations that may be used to test this assumption and discuss the puzzles and challenges that arise from this analysis.

You can download the talk here (pdf, 22 MB).

2013 May 31

Anatoly Klypin


Nature of dwarf spheroidal galaxies

Dwarf spheroidal galaxies were thought to be the simplest galaxies in the Universe. They do not have gas or star formation. They are dominated by dark matter. They do not rotate. Recent observational and theoretical results show that the galaxies are not simple. They became a center of one of the most difficult problems in cosmology: too-big-to-fail problem, which is states that structure of large dShp galaxies is not compatible with predictions of the standard cosmological model. I will show results, which show how the problem can be resolved. I will also discuss scenario of the origin of these galaxies.

You can download the talk here (pdf, 5 MB).

2013 Apr 30 11:00

Special Seminar: Alexander Wiegand


Minkowski functionals of the SDSS Luminous red galaxies

In this talk, we present the results of our Minkowski functional analysis of the structure of the galaxy distribution in the luminous red galaxy (LRG) sample of the Sloan Digital Sky Survey. With the discovery of larger and larger coherent structures, it is worthwhile to test the consistency of the observations with the standard models of structure formation. For this purpose, Minkowski functionals are very useful, as they contain more information than the usual two point statistics. For the analysis, we use Minkowski functionals in the boolean grain model, that allows a very precise and robust comparison. In addition, the Minkowski functionals in this model may be analytically related to a series of the (higher order) correlation functions of the distribution. This allows us to quantify the influence of higher order clustering beyond the simple two point correlations.

Comparing the observed Minkowski functionals to the functionals obtained from a set of N-body simulations, we find them basically consistent with each other. Expanding the functionals into a power series of integrals over n-point functions and comparing the coefficients with the theoretical prediction, gives also a consistent picture. Finally, we use the series expansion to investigate the importance of the higher order n-point functions for the shape of the functionals.

2013 Apr 26 10:30

Igor Karachentsev

Special Astrophysical Observatory, Russian Academy of Sciences

Low density structures in the Local Universe

We present results of our search for low-density associations of galaxies, as well as empty volumes in the Local Supercluster and its vicinity ( D < 45 Mpc). By percolation method we found 226 diffuse, non-virialized agglomerates with n>3 members. Eight the most populated among them ( n > 25) have following median parameters: linear size of ~6 Mpc, radial velocity dispersion of 170 km/s, virial mass-to-stellar mass ratio ~ 700 and a density contrast ~5. In the same volume, we also found 89 spherical cosmic voids having diameters from 12 to 24 Mpc. About 93% of them are overlapping, and form three hyper-voids. The largest one contains 56 initial spherical cells and extends in a horseshoe shape, enveloping the Local Volume and the Virgo cluster. A scarce population of the local voids are represented by dwarf late-type galaxies with a high gas content and moderate star formation rates. Most of them sit shallow near the surfaces of cosmic voids.

You can download the talk here (pdf, 2 MB).

2013 Apr 19 10:30

The Calar Alto Legacy Integral Field Area Survey (CALIFA) - science results so far

11:00 Rosa Gonzalez-Delgado (IAA Granada):

We apply the fossil record method based on spectral synthesis techniques to recover the SFH resolved in space and time for more than 100 galaxies from the CALIFA survey, which is gathering Integral Field Spectroscopy over the optical range and up to radial distances of 3 half light radii(HLR) of local (z = 0.005--0.03) galaxies. We investigate the SFH of galaxies and their trends of the radial structure as a function of the galaxy stellar mass and morphology. We show how the different galactic spatial sub-components ("bulge" and "disk") grow their stellar mass over time. We find that star formation history of bulges is more fundamentally related to the stellar galaxy mass, and in contrast disks is related with the local stellar mass surface density. We also obtain the spatially averaged and integrated galaxy properties, and how they are related with the properties at 1HLR.

11:30 Vivienne Wild (Uni St Andrews):

This part of the talk will use the Mice as a case study to introduce for the 3 different aspects of CALIFA data: line emission, stellar continuum and kinematics. The Mice are a major merger between two massive gas-rich spirals, observed between first passage and final coalescence. By combining with multiwavelength observations and comparison to hydrodynamic simulations, the impact of first passage on the progenitor galaxies is revealed. Finally, I will briefly summarise some of the emission line based results from CALIFA so far.

12:00 Mariya Lyubenova (MPIA Heidelberg):

This part of the talk will review our ongoing efforts to understand galaxy kinematics and dynamics along the Hubble sequence. CALIFA, due to it's supreme coverage in wavelength, spatial extent and morphological type of galaxies provides us with a unique setup to study simultaneously gas and stellar kinematics and the distribution of luminous and dark matter.

2013 Apr 15 15:00

Special Seminar: Elmo Tempel


Detecting filamentary pattern in the Universe: a catalogue of filaments

2013 Apr 12 10:30

Dmitry Klochkov

IAAT Tuebingen

Probing the configuration of the emitting region in accreting magnetized neutron stars

Study of accreting magnetized neutron stars (observed as X-ray pulsars) over the last 40 years has led to an understanding of the basic physical mechanisms operating in these sources. Nevertheless a number of key points are still unclear. There is no general agreement neither on the dimensions and shape of the X-ray emitting regions nor on the physical conditions inside them. Both are expected to depend on the pulsar luminosity and the magnetic field strength/configuration. In our work, we use the spectrum-luminosity dependences observed in X-ray pulsars on different time scales to probe the structure of the emitting region. Of particular importance are variations of the cyclotron absorption feature(s), whose centroid energy is proportional to the magnetic field strength at the site of emission. We performed a systematic study of the spectrum-luminosity dependences based on the X-ray data taken with INTEGRAL and RXTE on a sample of bright accreting pulsars. Our results indicate the presence of distinct types of spectral variations with flux which we interpret as a manifestation of different modes of accretion, i.e. different configurations of the accretion column/mound above the star surface. According to our model, different accretions regimes are realized in a source depending on whether its X-ray luminosity determined by the mass accretion rate is above or below certain critical values.

You can download the talk here (pdf, 8 MB).

2013 Apr 11 11:00

Special Seminar: Isha Pahwa

University of Dehli

Inflation in Higher Dimensional Gauss-Bonnet Cosmology

A Gauss-Bonnet term naturally appears in the action for gravity when one considers the existence of space time with dimensions more than 1+3. A variety of inflationary models can be obtained in such a scenario, once the scale factor for the hidden dimension(s) is allowed to be different from that for the visible ones. In particular, no inflaton field is required. The phase space has a rich structure with different types of solutions, both stable and unstable. For a large class of solutions, the scale factors rapidly approach an asymptotic exponential form. Furthermore, sufficient inflation can be obtained for only a modest compression of the hidden world, if the latter is of a sufficiently large dimension.

2013 Apr 09 13:00

Special Seminar: Elena Turitsyna

University of Aston

Fibre Bragg gratings, applications in astrophysics

The talk will include a brief introduction to fibre Bragg gratings and the methods of characterising them. I will present the algorithm used to model particular gratings, which can be used in astrophysics applications - for filtering OH-emission lines. The last results of fabricated grating will be presented and the problems that occur in modelling and fabrication of such gratings will be discussed.

2013 Mar 22

Federico Spada


Magnetic activity and fundamental parameters of solar-like stars

I will present the construction of theoretical models of solar-like stars (i.e., 0.1 < M/Msun < 1.25) and their comparison with the best available observations.

As their name implies, solar-like stars share many properties with the Sun: they have outer convection zones, believed to be the seat of dynamo action, which in turn powers magnetic activity and, via the magnetic wind braking, drives a non-trivial rotational evolution. A long-standing issue in the theory of low-mass stars is the existence of a disagreement between models and observations: observed radii are ~ 10% larger and effective temperatures are ~ 5 % cooler than expected from theory. Interestingly, the R and Teff discrepancies compensate to give about the same luminosity, suggesting a surface origin of the

Very precise measurements of stellar parameters, obtained from interferometry and double-lined eclipsing binaries, establish beyond doubt the reality of such a discrepancy; its correlation with magnetic activity and its possible resolution, based on stellar models including magnetic fields, will also be discussed.

2013 Mar 15

Benjamin Moster

MPA Garching

Constraints on galaxy formation from connecting galaxies and dark matter haloes

Ab initio galaxy formation models such as hydrodynamic simulations and semi-analytic models assume a physically motivated model and try to predict statistical properties, e.g. the stellar mass function. However, despite substantial progress, simplified and uncertain recipes must still be employed to model the formation of stars and black holes and the associated feedback processes. An alternative approach is to link galaxies and haloes statistically using the 'subhalo abundance matching' method. To this end we employ a redshift dependent parameterization of the stellar-to-halo mass relation, populate haloes and subhaloes in the Millennium simulations with galaxies and require that the observed stellar mass functions at different redshifts be reproduced simultaneously. The resulting relation is used in combination with merger trees extracted from the simulations in order to predict the mean assembly histories of the stellar mass components. I will discuss how this method can constrain the physical processes of galaxy formation, and present predictions of galaxy properties at high redshift.

2013 Mar 14

Special Seminar: Alexander Kashlinsky

NASA Goddard Space Flight Center

Looking at Infrared Background Anisotropies with Euclid - LIBRAE and first stars

I will discuss a new project, LIBRAE, of the cosmic infrared background (CIB) planned by NASA and ESA for the future Euclid satellite. LIBRAE will exploit planned Euclid imaging of both the Wide and Deep Survey regions at infrared and visible wavelengths in order to 1) measure the source-subtracted CIB structure (fluctuations) out to scales of a few degrees with better than ~1% accuracy. With this we will be able to clearly distinguish the nature and parameters of the populations responsible for the production of the CIB fluctuations. 2) Determine the Lyman break, and epochs, of the populations producing these fluctuations by expanding the SED of the measured fluctuations from 3-5 micron to 0.5-5 micron. 3) cross-correlate the measured fluctuations with optical, IR, X-ray, and microwave imaging from a number of other facilities. LIBRAE will identify the net emissions from the first stars era, lead to a better understanding the condition of intergalactic medium at that epoch, isolate the contributions from the first black holes and shed light on dust content at those times. The project has potentially transformative implications for understanding the emergence of the Universe out of the "Dark Ages".

2013 Mar 08

Roberto Mendez

Institute for Astronomy, University of Hawaii, Honolulu

Extragalactic planetary nebulae as kinematic tracers and distance indicators

I will explain the methods for extragalactic PN detection and slitless radial velocity measurements; summarize the various results obtained from the study of PN populations in about two dozen galaxies; present a list of unsolved problems, and describe some perspectives for future work.

You can download the talk here (pdf, 7 MB).

2013 Mar 07

Special Seminar: Mariya Lyubenova

MPIA Heidelberg

The complex nature of Nuclear Star Clusters in early-type galaxies

Recent observations have shown that compact nuclear star clusters (NSCs) are present in up to 80% of galaxies. However, detailed studies of their dynamical and chemical properties are confined mainly to spiral galaxy hosts, where they are more easily observed. In this talk I will present our study of the NSC in FCC 277, a nucleated elliptical galaxy in the Fornax cluster. We use a combination of adaptive optics assisted near-infrared integral field spectroscopy, Hubble Space Telescope imaging, and literature long slit data. We show that while the NSC does not appear to rotate within our detection limit of ~6 km/s, rotation is detected at larger radii, where the isophotes appear to be disky, suggesting the presence of a nuclear disk. We also observe a distinct central velocity dispersion drop that is indicative of a dynamically cold rotating sub-system. Following the results of orbit-based dynamical modelling, co-rotating as well as counter rotating stellar orbits are simultaneously needed to reproduce the observed kinematics. We find evidence for varying stellar populations, with the NSC and nuclear disk hosting younger and more metal rich stars than the main body of the galaxy. We argue that gas dissipation and some level of merging have likely played an important role in the formation of the nucleus of this intermediate-mass galaxy. This is in contrast to NSCs in low-mass early- type galaxies, which may have been formed primarily through the infall of star clusters.

2013 Mar 04

Special Seminar: Adriane Liermann


Stellar spectroscopy - mass loss and evolution of high-mass stars

High-mass stars evolve on short time scales giving strong feedback to the ambient interstellar medium in form of ionizing photons, mass loss and kinetic energy before they explode as supernova. With quantitative spectroscopy we can study the different phenomena associated with high-mass stellar evolution. In this talk I will present long-slit and integral-field spectra of high-mass stars in the Milky Way and the Large Magellanic Cloud taken with LBT-Lucifer I and VLT-Sinfoni. In combination with appropriate models their fundamental stellar parameters could be derived, mass-loss scenarios studied and the evolutionary status of the stars evaluated. These studies help to understand the mass-loss mechanisms during different phases of stellar evolution and to get a handle on the properties of the host population of these stars.

2013 Mar 01

Compute-Cluster and Cloud-Storage at AIP

An Overview of the AIP Compute-Cluster and Cloud-Storage will be given. Usage of these facilities will be explained.

2013 Feb 15 10:30

Sydney Barnes


Aspects of the Rotation of Cool Stars

This talk will focus on the rotation of cool stars, and touch on various other aspects related to stellar activity. The study of these activity-related properties seems to permit access to a number of aspects of modern stellar physics that are not possible with `standard' stellar models. Conversely, the rotation of cool stars is now known to be a dependent variable, and this dependence permits improved ways to access `classical' stellar properties such as age (via a method called gyrochronology). I will talk briefly about this method, and a couple of possible applications, such as determining a chronology for Galactic stars. However, the onus will be on attempts to understand what is going on within cool stars, and what the implications might be for the evolution of activity-related observables. Some implications for the history of our own Sun will also be mentioned.


2013 Feb 12 15:00

Special Seminar: Tanya Urrutia


Quasar Outflows in Luminous, Dust-Reddened Quasars

Quasar feedback - the influence of the black hole on the overall properties of its host galaxy - has been invoked to explain many properties in today's galaxies such as the scaling relations between the black hole mass and the bulge properties or the high end galaxy mass function. In the last few years there have been widespread efforts to find physical evidence for such feedback.

I will show results from studies of dust-reddened quasars, an early phase in a luminous quasar's life, in which we find signatures for powerful quasar outflows either in the ionization lines in the UV or in the molecular lines in the far-infrared. These outflows are powerful enough to influence the gas properties in the host galaxy and therefore the star formation efficiency. I will present statistical evidence of such effects and detail future efforts of characterizing the importance of such outflows on the overall properties of the host galaxy.

2013 Feb 01


Adi Nusser


Probing fundamental cosmological physics with large scale motions of galaxies

The standard cosmological model based on dark energy, standard gravity, and cold dark matter as the driver for structure formation has passed important observational tests related to the present distribution of matter on large scales (larger than a few 10s of Megaparsecs). It will be argued that deviations from the standard model can be further probed through signatures of the large scale motions (deviations from pure Hubble flow) of galaxies. Some constraints on f(R) and DGP gravity will be described using motions of galaxies in the nearby Universe. It will be shown how future surveys of ~ a billion galaxies like Euclid will allow constraints on dark energy models.

You can download the talk here (pdf, 8 MB).


2013 Jan 28 14:00

Special Seminar: Veronica Biffi

Triest, Italy

Synthetic X-ray observations of simulated galaxy clusters

X-ray observations provide us with an increasingly detailed pictured of galaxy clusters, for which a clear interpretation of the underlying physical processes is very challenging. While hydrodynamical simulations can currently address many questions about the cluster dynamics and physics, it is vital to find a direct and faithful way to compare their results to real X-ray observations. By means of the X-ray virtual telescope PHOX we can generate mock X-ray observations out of hydrodynamical simulations of galaxy clusters. In this way, we can address a number of interesting issues, such as the reconstruction of the cluster temperature distribution via spectral analysis or the investigation of scaling relations among global observable properties, e.g. luminosity and temperature. Furthermore I will show an application of the simulator to obtain high-resolution spectra of clusters, such those achievable with upcoming X-ray missions as ASTRO-H or ATHENA, from which a tight constrain on the intra-cluster medium (I CM) non-thermal velocity can be derived. This is particularly important since non-thermal motions in the ICM are believed, for instance, to play a non-negligible role in the pressure support to the total gravitating mass of galaxy clusters. Additionally, the L-T relation is explored in combination with the ICM velocity diagnostics, offering a promising way to identify disturbed clusters which is complementary to the commonly used morphological classification.

2013 Jan 15 10:00

Special Seminar: Tim Birks

Department of Physics, University of Bath

Photonic Crystal Fibres

A photonic crystal fibre is an optical fibre in which light is guided along its core by a pattern of air holes in the surrounding cladding. This gives the fibres properties that cannot be attained using more conventional fibres, such as endlessly single-mode guidance, high optical nonlinearity and even guidance in a hollow core.

2013 Jan 11


Moritz Guenther

(Harvard-Smithsonian Center for Astrophysics)

Accretion, winds and jets

Young stars and planetary systems form in molecular clouds. After the initial radial infall an accretion disk develops. The circumstellar envelope depletes and thus the absorption of the central star decreases. The high energy emission of these objects, the so-called classical T Tauri stars (CTTS) differs markedly from their main-sequence counterparts.
I will describe three different emission mechanisms that contribute to the observed X-ray and UV emission:

  1. A corona not unlike that observed on main-sequence stars.
  2. The accretion spot: The accretion disk does not reach down to the central star, but it is truncated near the co-rotation radius by the stellar magnetic field. The inner edge of the disk is ionized by the stellar radiation, so that the accretion has to be funneled along the magnetic field lines. On the stellar surface an accretion shock develops, which is observable in a wide wavelength range including X-rays and UV excess.
  3. Furthermore, many (if not all) accreting systems also drive strong outflows which are ultimately powered by accretion. However, the exact driving mechanism is still unclear. Several components could contribute to the outflows: Slow, wide-angle disk winds, X-winds launched close to the inner disk rim, and thermally driven stellar winds. In any case, the outflows contain material of very different temperatures and speeds.

Accretion and outflows in the CTTS phase do not only determine stellar parameters like the rotation rate on the main-sequence, they also could have a profound impact on the environment of young stars.

2013 Jan 10


Special Seminar: Katja Poppenhaeger

(Harvard-Smithsonian Center for Astrophysics)

How to X-ray an exoplanet

Many exoplanets orbit their host stars at close distances, with orbital periods of only a few days. The incident stellar flux can deposit sufficient energy in those planetary atmosphere to lift parts of it out of the planet's gravitational well, causing substantial mass loss. And indeed, mass loss of atomic hydrogen has been observed in UV spectral lines for a handful of planets. However, at the temperatures thought to be present in the planetary outer atmospheres, hydrogen is mostly ionized, so that these measurements lose their sensitivity at higher planetary altitudes. I will present the first X-ray detection of an exoplanetary transit in front of its host star; we find a surprisingly deep X-ray transit with three times the optical transit depth. This can be traced back to thin outer atmosphere layers of the planet, which are transparent at optical wavelengths but opaque to X-ray photons. I will end with a discussion about how present and future X-ray missions can provide new insights into exoplanetary atmospheres that are inaccessible at other wavelengths.


2012 Dec 21


Bettina Posselt

(Penn State University)

Not yet retired - X-ray emission of the old radio pulsar PSR J0108-1431

The high energy emission of radio pulsars provides interesting information about the extreme temperatures of the neutron stars and the accelerated particles around them. As neutron stars age they become less powerful, but surprisingly more efficient X-ray emitters. The X-ray properties of old pulsars are not well understood.

I will present our recent spectral and timing results of an X-ray study of PSR J0108-1431 with XMM-Newton. PSR J0108-1431 is the oldest and closest of the X-ray detected rotation-powered pulsars. I will discuss our results with respect to past studies of other old (and young) pulsars.

2012 Dec 14


Heike Rauer

(Institute of Planetary Research DLR, Berlin-Adlershof and Center for Astronomy and Astrophysics, TU Berlin)

Status and future of extrasolar planet detection by photometric transits

In this decade we have seen a rapid increase in our understanding of the nature of extra-solar planet systems and their host stars. Missions such as Corot and Kepler have confirmed that not only are extra-solar planets a common occurrence, but that multiple planetary systems are also the norm. The detection of hot low-mass, super-Earth planets like CoRoT-7b and Kepler-10b, has expanded our planet inventory towards small, rocky planets. The planned ESA Small Mission CHEOPS will extend the sample of planets with known radii by following-up planets previously detected from ground, e.g. by the radial-velocity method. Photometric ground-based surveys searching for transiting planets have been very successful in the past and aim towards increasing the number of e.g. mini-Neptune-like planets in future, e.g. like the NGTS survey (Next Generation Transit Survey) starting in the near future. However, whilst there has been significant progress in discovery and to some extent understanding of extra solar planets and their host star(s), major questions remain as we seek to reveal the presence of extra-solar planets harboring life. The PLATO mission is a proposed ESA M3 mission which will revolutionize our understanding of extra-solar planets, through its discovery of planets around hundreds of thousands of stars, orders of magnitudes more than previously known. This talk will provide an overview of the detection status of current and future transit surveys and will then describe the PLATO mission and science yield.

2012 Dec 11


Special Seminar: Daniel Angerhausen

(Rensselaer Polytechnic Institute in Troy, NY)

Exoplanet Atmospheres before JWST - Occultation spectrophotometry with current groud, space and airborne based platforms

In the last few years our knowledge of exoplanets has been revolutionized by the detection of statistically significant numbers of planets by platforms such as Kepler and CoRoT. Furthermore, the characterization of exoplanet atmospheres by the Hubble (HST) and Spitzer Space telescopes brought an 'Era of Comparative Exoplanetology'. By utilizing the transit method (measuring the small, wavelength-dependent variation in flux as an exoplanet passes in front of or behind its parent star), we are now able to characterize exoplanetary atmosphere. However, due to its Earth-trailing orbit, Spitzer will inevitably become unavailable for further observations in the near future and is only capable of photometric observations in limited bandpasses in its “warm” mission phase. HST is scheduled to remain on-line until ~2020, but the current instrumentation limits HST to wavelengths shorter than 1.7 μm.

In my talk I will describe how the airborne-based platform SOFIA and ground-based multi-object-spectrometers will help to close this NIR characterization bottleneck until the start of JWST: I will present the proposals chosen in SOFIA's Cycle 1 in this field as well as the 2nd generation instrument concept NIMBUS (near-infrared multi-band ultraprecise spectroimager). Furthermore I will display recent observations with Keck's MOSFIRE instrument.

2012 Dec 10


Special Seminar: Sunghye Baek


Identifying AGN-powered Lyman Alpha Emitters

The most natural explanation for the large Lya luminosities is associated with star forming activities. Short-lived, massive stars produce large amount of UV photons and H-atoms recombine on a short time scale in the dense interstellar medium emitting Lya photons. Interestingly, a fraction of LAEs seem to host an Active Galactic Nuclei (AGN). I will present our recent work in this talk, radiative transfer cosmological simulations of a prototypical z=6.6 LAE. I will show that this indeed is possible and introduces a simple but solid diagnostic tool to unambiguously assess if the LAE luminosity is powered by an AGN or by starburst.

2012 Dec 07


Barry Rothberg


The Janus Effect: How Multiple Stellar Populations Affect the Observed Dynamics of Major Mergers

A key goal in astrophysics is the ability to identify the progenitors of present-day galaxies. Gas-rich major mergers in the local Universe, particularly Luminous and Ultraluminous Infrared Galaxies (LIRGs/ULIRGs) present a unique opportunity to study the formation of elliptical galaxies, including the most massive which will become QSO host galaxies. Yet, increasingly, a number of observational and theoretical studies suggest that both locally and afar, gas-rich mergers are not a major driving force in the formation of massive galaxies or responsible for the majority of star-formation at any given epoch. The ultimate implication is that Lambda-CDM cosmology and our current understanding of galaxy formation is incorrect. Locally, this is driven by direct measurements of dynamical masses that show LIRGs/ULIRGs form only low-intermediate mass ellipticals. I will present results which demonstrate that our understanding of the dynamical properties of major mergers in the local Universe relies not only upon instrumental resolution and our ability to collect photons, but on our ability to properly disentangle (and use to our advantage) the complicated nature of mergers. The presence of multiple stellar populations and dust affects what we observe at different wavelengths, and until recently, has led to a major underestimation of the dynamical masses of LIRGs/ULIRGs by at least an order of magnitude. I will discuss these new and ongoing results in the context of the ULIRG-QSO connection, and whether this discrepancy is limited only to LIRGs/ULIRGs or if it affects our ability to measure the complete dynamical properties of all galaxies at all epochs.

2012 Nov 30


Holger Israel

(AIfA Bonn)

Cosmology with Weak Lensing Clusters: The 400d Survey and Beyond

Galaxy clusters are of particular interest to cosmology: Their mass function, depending on both the expansion history of the Universe and structure formation enables us to constrain cosmological parameters, e.g. the equation-of-state parameter (time variability) of Dark Energy.
Here, I present the current status of the 400d Weak Lensing Programme, following up a sample of relatively distant (0.35<z< 0.90) X-ray selected clusters. Determining cluster masses by weak lensing, we obtain an independent test of the X-ray analyses for the 400d clusters. Once completed, the WL follow-up allows us to cross-calibrate X-ray and WL mass measurements. Such scaling relations will be contributing crucially to next-generation surveys.
I present the analyses for the first eight clusters for which we determined weak lensing masses based on observations with MMT/Megacam, which we demonstrate to be well-suited for weak lensing. Determining masses for all clusters despite unfavourable data conditions, our analyses highlight the capabilities of WL as well as directions for technical improvement. I highlight the case of a cluster seen through a filament, for which we are able to model the massive foreground structure.
Showing the first results for lensing - X-ray scaling relations with our distant sample of "average-mass" clusters, I conclude with an outlook on some of the planned Dark Energy surveys including galaxy clusters and weak lensing.

2012 Nov 23


Peter Creasey


Supernova feedback at high resolution

Cosmological numerical simulations of galaxy formation are strongly dependent upon the strength and nature of the scheme used for supernova feedback. In this talk I will discuss how the galaxy mass function can be used to infer the mass ejection rates due to feedback process and compare with the difficulty of determining these from first principles. I will also describe a set of converged hydrodynamical experiments that in principle allow us to calibrate these rates, toward the goal of producing realistic galaxy populations.

2012 Nov 16


Andrea Maccio


MaGICC: Making Galaxies in a Cosmological Context

In a universe dominated by Cold Dark Matter (CDM) and a cosmological constant, galaxy formation and evolution is a complex combination of hierarchical clustering, gas dissipation, merging events and secular evolution. Given the high non linearity of the problem, computer based numerical simulations are now a day one of the most powerful tools to unveil the galaxy formation process.
In my talk I will first explain how cosmological numerical simulation are performed and I will review recent results in this field. I will then present the MaGICC project (Making Galaxies in a Cosmological context) a large simulation campaign we recently started at the MPIA in Heidelberg. Our model is very successful in reproducing several properties of observed (disc) galaxies, nevertheless several questions still remain to be answered before we can claim a fully understanding of galaxy formation.

2012 Nov 09


Markus Roth

(Kiepenheuer-Institut für Sonnenphysik, Freiburg)

Helioseismology of the solar meridional flow

The Sun's meridional flow is a large-scale flow observed on both hemispheres of the solar surface. Detailed knowledge on this flowin the solar interior is important for understanding the solar dynamo action. Undesirably, over the bulk of the convection zone, the flow has not been seismically determined. With methods of local helioseismology the flow was measured only in the outer 15 Mm of the Sun in the past. Today, new approaches of global and local helioeismology are developed that promise measuring the meridional flow down to the bottom of the convection zone. In this talk I will describe these new approaches and the first results of these measurements.

2012 Oct 19


Sergei Shandarin

(Univ Kansas)

Tessellation Approaches to Analysis of Cosmic Web

The Cosmic Web discovered at the end of 20th century remains not fully understood even in cosmological N-body simulations where the full dynamical information is easily available. The majority of cosmologists probably would agree that the web is made of four distinct geometrical types of structure, ie. relatively compact clusters, filaments, walls/pancakes, and nearly empty voids. However, they hardly agree on the fractions of mass and volume occupied by these structures. Although it seems paradoxical recent progress in studies of the structure of the Cosmic Web in six-dimensional phase space may help to better understand its geometry and topology in three-dimensional configuration space. I will discuss the novel method based on the tessellation of the phase space sheet of Dark Matter, new results and the future prospects.

2012 Oct 12


Thomas R. Ayres

(Center for Astrophysics and Space Astronomy of the University of Colorado, Boulder, U.S.A.)

C/O isotopes in the Sun & the solar oxygen abundance

Recent results from NASA's Genesis Discovery Mission, whose objective was to directly capture CNO ions from the solar wind, suggest that the Sun is isotopically `lighter' than the Earth. This is in line with theoretical understanding of fractionation processes in the primitive solar nebula, but contrary to a series of solar photospheric measurements -- based mainly on isotopic variants of the CO molecule, notably an early study by Hall, Noyes, & Ayres (1972) -- that suggested that the Sun might be as `heavy' or heavier than the Earth. Now, 40 years later, a whole new series of tools have been brought to the problem, including (most importantly) ab initio solar 3D convection models, as well as broad band measurements of the infrared CO bands (2-6 microns) from the highly precise ATMOS FTS spectrometer in orbit (on Space Shuttle, in the 1990's). I show how the new CO spectra and new 3D models join to trim some isotopic weight off the Sun, and tip the spectroscopic view toward that of Genesis, although not completely the whole way. The story is a cautionary tale concerning the limitations of historical 1D spectrum synthesis, which produces especially bad results for the particular case of the molecules with their ultra-sensitivity to atmospheric thermal properties; but also a glimpse of what can be accomplished with high-precision "forensic" spectroscopy of the solar plasma.

2012 Oct 10


Thomas R. Ayres

(Center for Astrophysics and Space Astronomy of the University of Colorado, Boulder, U.S.A.)

Cool Stars: So Hot Right Now

Space Telescope Imaging Spectrograph (STIS) was the workhorse for cosmic ultraviolet spectroscopy from its 1997 installation in Hubble until its untimely failure in 2004. In fact, with the effective loss of the Far-Ultraviolet Spectroscopic Explorer in 2006, the study of solar-like activity on other stars -- advantageously viewed in the UV -- at that time entered an observational “Dark Ages.” Today, stellar UV astronomy is enjoying a welcome rejuvenation, thanks to Hubble Servicing Mission 4 in May 2009, which not only installed the super-sensitive Cosmic Origins UV spectrograph (COS), but also miraculously repaired STIS. This talk will explore some of the projects that have been carried out with both Hubble UV spectrographs over the past several years post-SM4, focusing on cool stars; including the Advanced Spectral Library (ASTRAL), which has obtained full coverage high-resolution UV “atlases” of eight iconic late-type stars; and the so-called COCOA-PUFS joint HST/Chandra UV/X-ray campaign on the enigmatic ultra-fast rotating yellow giant, FK Comae Berenices.

2012 Oct 04 15:00 Special Seminar: Robert Content

(Australian Astronomical Observatory Sydney, Australia)

Integral Field Systems

I have been involved with the design of integral field systems since 1995 at the Centre for Advanced Instrumentation of Durham University then called the Astronomical Instrumentation Group. I will describe the important characteristics of the 4 main groups of Integral Field Systems (IFSys), not 3 as usually believed. The fourth is not well known and not much used but may be the first to be on a telescope. We designed and built a series of IFSys of the 3 other group types for many telescopes including UKIRT, WHT, Magellan, Gemini North and South, VLT and JWST and as laboratory prototypes. I will give a brief history of these systems. I will especially mention the progress I brought in each of the 4 groups along the years.

2012 Oct 04 11:00 Special Seminar: Gwangson Choe

(Kyung Hee University, Yongin, Korea)

Energetics and Dynamics of Large Scale Solar Eruptions

Coronal mass ejections involve expulsion of mass and magnetic flux and stretching of field lines into the interplanetary space. The time scale of an eruption is much shorter than the time scale of energy buildup and the life span of structures to erupt such as prominences. Thus, the eruption is regarded as a spontaneous process rather than a simultaneously driven process. The pre-eruption stage is considered as a meta-stable state having more energy than all the states appearing in the course of the eruption, one of which is the open field state. The trigger of the eruption just plays the role of pushing the system into lower energy states. This talk illuminates two issues: (1) how a configuration with more magnetic energy than the open field can arise, and (2) how a coronal magnetic field system evolves from a mere gathering of small scale flux tubes into an eruption-vulnerable high energy meta-stable state of a large scale and finally moves into eruption. Our attention is focused on statics and dynamics multiple flux systems since we have found that such systems can have more energy than open fields. Our study reveals that a multiple flux system under a line-tying condition evolves stepwise through different multiple flux systems toward eruption. An observational example for our model will also be presented.

2012 Sep 19 15:00 Special Seminar: Rene Fassbender

(Max-Planck-Institute for Extraterrestrial Physics, Garching)

The X-ray luminous Galaxy Cluster Population at 0.9<z<~1.6

XMM-Newton has been the unrivaled workhorse for X-ray selecting new high redshift galaxy clusters in the first half of cosmic time, in particular based on serendipitous archival searches. The most successful survey in this field has been the XMM-Newton Distant Cluster Project (XDCP), which has compiled a spectroscopically confirmed X-ray cluster sample of ~40 systems at z>0.8 (23 at z≥1) with a homogeneous redshift coverage all the way out to z~1.6. This talk will shortly review recent advances in distant cluster research, present the properties of the most distant massive X-ray luminous galaxy clusters up to z~1.6, discuss the radial distribution of AGN in distant cluster environments, and give an outlook on the eROSITA prospects for revealing and studying the z>0.8 cluster population.

2012 Sep 17


Special Seminar: Paula Jofre

(Max-Planck-Institute for Astrophysics, Laboratoire d'Astrophysique de Bordeaux)

On the age determination of Milky Way halo field stars

I present a study of ages of field stars from a sample of the Sloan Digital Sky Survey. The results are consolidated with a set of globular clusters and show that this stellar sample is composed by one dominant population of 10-12 Gyr. This supports the Eggen's formation scenario, which claims that the inner halo of the Milky Way formed rapidly, probably during the collapse of the proto-Galactic cloud.

2012 Sep 07


Alexander Kashlinsky

(Goddard Space Flight Center)

Cosmic Infrared Background and new cosmological populations

Cosmic infrared background (CIB) is produced by emissions from luminous objects spanning the entire history of the Universe including from sources, such as first stars, which are inaccessible to individual telescopic studies. CIB fluctuations, in particular, can be more readily discerned than the actual mean level allowing to overcome the significant Galactic and Solar system foregrounds at NIR wavelengths. I will report on the recent measurements of the CIB fluctuations at near-IR using deep exposure data obtained by the Spitzer Space Telescope. Previous measurements by our group out to scales as large as ~5' had seen the first indication of excess fluctuations above those expected from ordinary galaxies. Recently, these have been extended to sub-degree scales using new data obtained in the course of the 2,000+ hour Spitzer Extended Deep Survey. I will report these new observations, the methods to robustly uncover CIB fluctuations there and the implications of th measurement in isolating new cosmological populations, such as residing during first stars epochs.

You can download the talk here (pdf, 1.4 MB).

2012 Aug 10


Jo Bovy

(IAS, Princeton)

Precision measurements of the Milky Way's disk structure and dynamics

Observations of the structure and dynamics of different stellar populations in the Milky Way's disk provide a unique perspective on disk formation and evolution. I will discuss how current and future data sets that provide detailed kinematics and elemental abundances beyond the Solar neighborhood lead to qualitatively new tests of internal and external disk evolution models. In particular, I will show recent results from a dissection into mono-abundance components of the Galactic disk based on SDSS/SEGUE data. These results show that the individual components are simple, but exhibit very different spatial structure, and they lend direct observational support for inside-out formation models for galactic disks. I will also discuss recent results on a new measurement of the Milky Way's rotation curve from APOGEE.

You can download the talk here (pdf, 7.6 MB).

2012 Aug 02


Special Seminar: Joel Johansson

(Stockholm University)

Supernovae cosmology: level up or game over?

A key goal of supernova cosmology is constraining the nature and properties of dark energy through detailed measurements of the Universe's expansion history. We have now a precise account of the expansion history of the last 7 Gyrs, but progress in distinguishing between different dark energy models is today limited by systematic uncertainties, which are equal in size to the statistical errors.

I plan to discuss ongoing efforts to adress some of the potential sources of systematic uncertainties, i.e dimming/reddening by dust and the progenitor systems of Type Ia supernovae. Furthermore, I will present ideas on how to exploit gravitational lensing by galaxy clusters to do find magnified supernovae, giving us the means to explore another 4 Gyrs of the expansion history.

2012 Jul 26


Special Seminar: Alberto Sesana

(AEI Potsdam)

Massive Black Hole Binaries: formation, dynamics and gravitational waves

In the next decade the detection of gravitational waves (GW) will be a reality, opening a completely new window on the Universe. Massive black holes (MBH) binaries (MBHBs) are expected to be among the primary actors on this upcoming stage. I review our current understanding of MBH(B) formation, evolution and dynamics during the cosmic history, I will discuss detectability with proposed space interferometers (LISA/eLISA) and ongoing and forthcoming pulsar timing arrays, and discuss prospects to do multimessenger astronomy by exploiting observations of putative electromagnetic counterparts.

2012 Jul 10


Special Seminar: Sourav Mitra

(Hasih-Chandra Research Institute Allahabad, India)

Reionization constraints using principal component analysis

Reionization is a complex process whereby hydrogen (and helium) in the Universe is ionized by the radiation from first luminous sources. Theoretically, the importance of the reionization lies in its close coupling with the formation of first cosmic structures and hence there is considerable effort in modelling the process. In this talk, we will present our recent works on some aspects of this subject. In particular, we will give an overview of the semi-analytical approach (Choudhury & Ferrara (2005,2006)) to study the observational constraints on reionization. We implement and investigate a method to do a detailed statistical analysis using Principal Component Analysis (PCA) technique. We also discuss different observations related to reionization and show how to use PCA for constraining the reionization history.

2012 Jun 01


Timur Doumler


Constrained Local Universe simulations from galaxy peculiar velocities

Numerical simulations are a powerful tool to study the formation and evolution of the large-scale structure of the Universe in the cosmological context. With the Constrained Realizations method it is possible to create simulations that faithfully reproduce the large-scale structure of the observed Local Universe. The crucial step is to generate appropriate initial conditions for these simulations from the available observational data. Our approach is to use galaxy peculiar velocities, which can be derived from galaxy redshifts and independent measurements of their distance.

In this talk, I will describe recent improvements on this technique, which take into account the non-linear evolution of the cosmic matter distribution. By applying a Lagrangian reconstruction to the peculiar velocities, we reconstruct the displacements and initial positions of observed galaxies. In this way we can generate a significantly better estimate of the initial conditions of the Local Universe.

2012 May 25


Romauld Tylenda

(N. Copernicus Astronomical Center, Torun, Poland)

V1309 Scorpii: a Rosetta stone in the field of red novae and contact binarie

Red novae (red optical transients) form a small class of stellar eruptions, which at first sight can be (and were) considered as particular cases of classical novae, but they are not. Their principal observational characteristic is that during outburst they evolve to progressively lower effective temperatures and fade as late M-type (super)giants. V838 Mon, which erupted in 2002, is the most famous (mainly due to the spectacular light echo event, which accompanied the eruption) and best studied case in the class. We have shown, mainly on the analysis of V838 Mon, that the eruption of this type cannot result neither from classical nova thermonuclear runaway nor from late He-shell flash. Instead, we proposed that red nova eruptions result from mergers of two stars.

V1309 Sco erupted in September 2008 and was initially classified as a classical nova. Its spectroscopic evolution during and after the eruption clearly showed this was a red nova. Very fortunately it appeared that the object lies in a sky field systematically monitored in the OGLE project led by Warsaw University Observatory in Chile. As a result the OGLE archive provided us with an extraordinary set of data: more than 1300 photometric measurements of the object between 2001 and the discovery of the eruption. Our analysis showed that the progenitor of V1309 Sco was a contact binary quickly evolving to the merger of the components.

2012 May 24


Special Seminar: Antonela Monachesi

(University of Michigan)

Resolving stellar populations of nearby galaxies: The SFH of M32 and the color profile of M81's stellar halo

The detailed study of the resolved stellar populations in the nearby Universe is a powerful tool to understand how galaxies form, interact and evolve across cosmic time. In this talk I will focus on the stellar populations of two very distinct galaxies: M32 and M81.

The Local Group galaxy M32 is a compact elliptical galaxy, satellite of M31. Although a low-luminosity galaxy, M32 is the nearest system with structural properties reminiscent of giant ellipticals. I will present the most complete inventory of the resolved stellar populations of M32 and its SFH at 2 arcmin from its center from both qualitative and statistical analyses of very high-resolution and deep HST observations.
During the second part of this talk, I will discuss an ongoing study of 19 fields near the large spiral galaxy M81. The fields, observed as part of the GHOSTS survey, probe the stellar halo of M81 out to projected distances of ~ 50 kpc along the minor axis of M81, an unprecedented distance for halo studies outside the Local Group. I will present the color profile of M81's stellar halo and compare our results with cosmologically motivated models.

2012 May 15


Special Seminar: Arianna DiCintio

The density profile of subhaloes in the CLUES simulation: implication for the MIlky Way's dwarf spheroidals

We use dark matter only and full hydrodynamical Constrained Local UniversE Simulations (CLUES) of the formation of the Local Group to study the density profile of subhaloes of the simulated Milky Way and Andromeda galaxies. We show that the Einasto model provides the best description of the subhaloes’ density profile, as opposed to the more commonly used NFW profile or any generalization of it. We further find that the Einasto shape parameter n_E is strongly correlated with the total subhalo mass, pointing towards the notion of a non-universality of the subhaloes’ density +profile. Assuming now that the dSphs of our Galaxy thus follow the Einasto profile and using the maximum and minimum values of n_E from our SPH simulations as a gauge, we can improve the observational constraints on the R_max-V_max pairs obtained for the brightest satellit +galaxies of the Milky Way. When considering only the subhaloes with -13.2 < M_V < -8.8, i.e. the range of luminosity of the classical +dwarfs, we find that all our simulated objects are consistent with the observed dSphs if their haloes follow the Einasto model with 1.6<n_E<5.3. The numerically motivated Einasto profile for the observed dSphs as well as the observationally motivated magnitude cut for the simulated subhaloes will eliminate the ”massive failures” problem and results in a perfect agreement with observations, if the Milky Way mass is ~8x10^11 Msun.

2012 May 11


Marcus Geller


Magnetic instabilities and liuid metal laboratory experiments

Many astrophysical phenomena (such as the slow rotation of neutron stars or the rigid rotation of the solar core) can be explained by the action of magnetic instabilities in the radiative zones of stars. Especially non- axisymmetric instabilities like the Azimuthal magnetorotational instability (AMRI) and the Tayler instability (TI) are appropriate candidates. In order to place the theory of this instabilities on a safe fundament, they have been realized in laboratory experiments. The talk will give details about simulations of liquid metal experiments and its lab realizations, shows results and explains why laboratory astrophysics helps to understand real phenomena inside stars.

2012 May 08


Special Seminar: James W. Beletic

(TELEDYNE Imaging Sensors, USA)

The Fantastical Discoveries of Astronomy made possible by the Wonderful Properties of II-VI Materials

The universe is an amazingly huge place. While humankind has directly explored Earth’s sister planets with space probes, we don’t have the means to venture beyond the solar system, and so almost all information about the universe comes from sensing light that happens our way. Astronomy is constantly striving to find better ways to sense the feeble amount of energy from distant stars and galaxies. This quest has led to a new generation of very large telescopes (up to 10-meter diameter) on the ground and the deployment of the 2.4-meter Hubble telescope in space.

Ground-based astronomy will soon begin construction on an even more ambitious generation of 30-meter class extremely large telescopes (ELTs), and the James Webb Space Telescope’s 6.5-meter mirror will launch by the end of the decade. Possibly more important than the development of bigger telescopes is the rapid advancement in solid state detector technology.

The detector revolution was led by silicon CCDs (IV material) starting in the 1970’s for sensing visible light, but the II-VI materials (HgCdTe) that were developed during the past two decades for sensing infrared light have made the most significant difference in astronomy. Long before the CCD, astronomers could detect visible light with the human eye and photographic plates, but until recently, infrared astronomy was not possible.

Infrared light is the only way to study a wide range of astronomical phenomena. As known from terrestrial applications, infrared light propagates through dust and infrared light is required for sensing cooler objects. More important for astronomy, the universe has been expanding since the Big Bang and the expansion of the universe has redshifted the ultraviolet and visible light of distant objects into the infrared. The distant universe is an infrared universe and several of the next generation facilities (JWST, dark energy missions, the ELTs) will rely mainly, if not entirely, on infrared detectors made from the II-VI materials whose features enable modern astronomy. This talk will present the cutting edge astronomy that is made possible by the wonderful properties of II-VI materials, including:

  • ability to tune the cutoff wavelength to optimize instrument performance
  • substrate removal that enables simultaneous detection of visible and infrared light
  • extremely low dark current (0.01 electrons per pixel per sec for 5 micron cutoff)
  • high quantum efficiency (>80%)
  • very low noise readout (3 electrons rms, after multiple sampling)
  • large format arrays (2K×2K is standard today, and 4K×4K is in development)
  • high operability (>99%)

2012 May 04


Wolfgang Steffen

(Instituto de Astronomica, UNAM, Ensenada, Mexico)

Astrophysical simulations with interactive computergraphi

A multi-purpose interactive astrophysical modeling system is presented. The system called “Shape” includes an interactive 3D environment to construct morpho-kinematic model structures on which radiation transfer and hydrodynamic evolution can be computed. The built-in prototypical hydrodynamics module distinguishes itself from conventional systems through its 3D interface and interactivity before and during simulation that requires no programming intervention by theuser. The hydrodynamics is highly parallelized and is computed on the Graphical Processing Unit (GPU). Visualization and analysis can be performed within Shape. Hydrodynamics and 3D-mesh based objectscan be mixed which allows for the modeling, analysis and visualization of highly complex objects.

2012 May 03


Special Seminar: Jaime Forero-Romero


New topics in high-z galaxy formation

There are thousands of confirmed detections of star forming galaxies at redshifts z>4. These observations rely primarily on the detection of the spectral Lyman Break and the Lyman-alpha emission line. I will present results based on hydrodynamical simulations aimed at constructing a panchromatic picture of this high redshift galaxy population. I will show how this model successfully reproduces the observational constraints from Lyman Break Galaxies (LBGs) and Lyman-alpha emitters (LAEs) at 5<z<7. Based on this model and recent observational results I will argue that three new elements should be considered in the interpretation of upcoming observations of high-z galaxies: stochasticity effects at low star formation rates, the impact of using molecular gas to model star formation and the necessity for AGN feedback at high redshift.

2012 Apr 27


Jason Nordhaus

(Rochester Institute of Technology)

Recent Advances in Core-Collapse Supernova Theory

For approximately half a century, core-collapse supernovae have posed a vexing puzzle for theorists despite being a major ingredient (and uncertainty) in fields ranging from stellar and galaxy evolution to the interstellar medium. Historically, advances in core-collapse theory have been linked to advances in computing power and software. Supernovae are inherently multi-dimensional objects in which neutrino transport, gravity, hydrodynamic instabilities and convection play important roles. Three-dimensional simulations incorporating sufficient physical fidelity require extensive high-performance computing resources and codes efficient enough to use the associated architecture. In this talk, I will highlight recent advances in the field. In particular, I will discuss the dependence of spatial dimension on the viability of the delayed-neutrino mechanism and the origin of pulsar kicks.

You can download the talk here (pdf, 20 MB).

2012 Apr 24


Special Seminar: Eberhard Wiehr


Line Profiles of Ionized and Neutral Helium in Solar Prominences

He II and He I lines are observed in aiescent prominences using NaD2 as a tracer for prominence candidates of sufficient He II emission strength. The low scattering in the Gregory Coud\'e telescope at the IRSOL observatory in Locarno allows an accuracy near 10-6 of the disk center intensity. Sufficiently bright He II emissions occurred in only 4 among dozens of prominences and are characterized by very small non-thermal line broadening and velocity shifts, yielding narrow line profiles without wiggles. Considering the fine-structure boadening, He II 4686 is 1.5 times broader than He I 4472 triplet line which, in turn, is 1.1 times braoder than the He I 5015 singlet line. Possible scenarios to explain this finding will be discussed.

2012 Apr 20


Javiera Guedes

(ETH Zürich)

The Eris Simulation: Forming Realistic Milky Way-like Galaxies Through Cosmological Simulations

Simulations of the formation of late-type spiral galaxies in a cold dark matter universe have traditionally failed to yield realistic candidates. The successful formation of Milky Way-sized disks requires the correct treatment of complex baryonic physics at sub-grid scales, particularly gas cooling, star formation, and supernovae feedback. In this talk, I will review some of the challenges involved in forming massive disk galaxies and I will present "Eris", a realistic late-type spiral galaxy formed in a high-resolution cosmological simulation. Eris appears to be the first cosmological hydrodynamic simulation in which the galaxy structural properties, the mass budget in the various components, and the scaling relations between mass and luminosity are all consistent with a host of observational constraints.

You can download the talk here (Guedes_AIP.key, 922 MB).

2012 Apr 19


Special Seminar: Abhijit Bendre


Simulations of supernova-driven galactic turbulence

The presentation is a report about the first results obtained in a PhD student project.

2012 Apr 17


Special Seminar: Günther Rüdiger / Manfred Küker


The Cross Helicity at the Solar Surface by Simulations and Observations

In order to model the cross helicity at the solar surface, magnetoconvection under the presence of a vertical large-scale magnetic field is simulated with NIRVANA. The robust result of the calculations is that the cross helicity can well be represented by the observable correlation of the vertical flow and the vertical field. The characteristic helicity speed as the ratio of the eddy diffusivity and the density scale height results to 1.1 km/s. This value coincides with the data of the Japanese HINODE satellite and the Swedish 1-m Solar Telescope. Both simulations and observations thus lead to 1012cm2/s as the sofar unknown eddy diffusivity at the surface of the quiet Sun.

2012 Apr 17


Special Seminar: Elmo Tempel

(Tartu Observatory, Estonia)

Orientation of galaxies in filaments: 3D photometrical modelling of galaxies and filamentary structure in the SDSS

We search for and find evidence that the spin axes of galaxies relative to their host filaments are not randomly distributed. Similarly to dark matter haloes in N-body simulations, spin axes of fainter galaxies are weakly aligned parallel to filaments, whereas more luminous galaxies have orthogonal alignment. To find the spin axes of galaxies, we used the 3D photometrical model of galaxies. This model allows to estimate relatively accurately the inclination angle of galaxies, whereas in 2D models the inclination angle is degenerate with the disc thickness. To search for filaments in the cosmic web, we use a three-dimensional object point process, which help to find the filaments and also defines the orientation of a filament.

In my talk, firstly, I describe the 3D photometrical model of galaxies and how accurately it restores the structural parameters and inclination angles of galaxies. Secondly, I describe the method that we used to find filaments and I demonstrate how good are the detected filaments. Finally, I combine these two results and search for correlation between filaments and spin axes of galaxies.

2012 Apr 17


Special Seminar: Enn Saar

(Tartu Observatory, Estonia)

Shadows of Baryonic Oscillations

Baryon Acoustic Oscillations (BAO) are a feature imprinted in the density field by acoustic waves travelling in the plasma of the early universe. Their fixed scale can be used as a standard ruler to study the geometry of the universe. BAO have been detected in the CMB and in the galaxy distribution, using correlation functions and power spectra. We searched for real-space structures associated with this feature -- spherical shells with a relatively small density contrast, surrounding high density central regions.

We designed a specific wavelet adapted to the search for shells, and used different mass tracers for the shells and for their centers. For the SDSS, we used the 'Main' catalogue galaxies for the shells, and LRGs as tracers of the high density central regions. We found BAO-size shell-like structures in the density field, with LRGs preferentially located close to the centres of the shells. As these shells are real spatial structures, the BAO phenomenon can be studied in detail by examining those shells; I describe preliminary results obtained by stacking of the shells.

2012 Apr 17


Special Seminar: Hongqi Zhang

(Beijing, China)

Helicity from Solar Observations

The helicity is important because it represents the basic topological configuration of the magnetic field the in solar atmosphere. The distribution of magnetic helicity in the solar atmosphere is presented by means of the observational (vector) magnetograms, etc. The comparison of observational helicities with magnetic ones in the solar atmosphere is also an important topic. The diagnostic of helicities provides an important chance for the confirmation on the generation of magnetic fields from the sub-atmosphere and also solar dynamo models. I would like to introduce some results of a recent study on helicity topics.

Future (ground and space) solar observational projects in China are also briefly introduced.

2012 Apr 13


Luigi Guzzo

(INAF-OAB, Italy)

Understanding Cosmic Acceleration with Galaxy Redshift Surveys

After less than fifteen years, the discovery that the Universe is accelerating emerges as one of the turning points in the history of cosmology, as witnessed by the 2011 Nobel Prize in Physics to Perlmutter, Riess and Schmidt. Yet, the origin of the accelerated expansion is a mistery. One possibility is that the Universe is permeated by a "dark energy" which gives rise to a gravitational repulsion. Alternatively, perhaps the very equations of General Relativity need to be modified or generalized to higher-dimensional worlds.

In my talk I will first recall the historical developments and review these general ideas. I will then discuss current perspectives for understanding the nature of cosmic acceleration using large surveys of galaxies. Breaking the degeneracy between dark energy and modified gravity requires measuring both the expansion rate and the growth rate of structures. This can be obtained from galaxy redshift surveys, mapping the large-scale distribution and dynamics of galaxies, of which I will show some new examples. Complementarily, one can use large high-resolution imaging surveys from space, to obtain a "tomography" of the distribution of dark matter using the weak-lensing effect. Both these techniques are at the core of Euclid, the recently approved ESA mission that promises to reach percent accuracies on cosmological parameters, with unprecedented control of systematic effects.

You can download the talk here (pdf, 33 MB).

2012 Apr 05


Sladjana Nikolic

(MPIA Heidelberg)

Supernova in 3D: VIMOS IFU observations of SN 1006

We present three-dimensional spatial-spectral mapping of the fast Balmer-dominated shocks surrounding the northwestern rim of the remnant of supernova (SN) 1006. We combine high spatial and spectral resolution to show that the physical characteristics of the shocks exhibit a strong spatial variation across different locations. Using models which do not take cosmic ray physics into account, we compute shock velocities and electron-to-proton temperature ratios based on observations of narrow and broad Halpha emission. Additionally, we are able to detect non-Gaussianity in the broad Halpha lines. Taken together, our results point to the presence of a population of non-thermal protons associated with the Balmer-dominated shocks, which we identify as low-energy (~10--100 keV) hadronic cosmic rays.

2012 Mar 23


Michael Kramer

(MPIfR Bonn)

Fundamental physics with radio astronomy

It order to understand the Universe and its evolution we need to understand the fundamental laws of nature. Radio astronomy is an ideal tool to provide insight into fundamental physics that is otherwise not obtainable. While the observed photons are of low energy, they are often the result of the most energetic processes in the cosmos. They carry information from the most extreme objects in the Universe (e.g. neutron stars), and their properties (namely polarisation and arrival times) reveal unique information about the only two fundamental long-range forces, electromagnetism and gravity. In this talk, I concentrate in particular on the study of gravitation and our current best description provided by the theory of general relativity and its alternatives.

You can download the talk here (pdf, 12 MB).

2012 Mar 14


Special Seminar: Pirin Erdogdu

(UCL, London)

The 2MASS Redshift Survey: Reconstructed Density and Velocity Fields and the Local Group Dipole

We present the updated reconstructed real-space density and velocity fields from the final release of the Two Mass Redshift Survey (2MRS) which includes 44,599 galaxies with extinction corrected magnitudes brighter than Ks = 11.75. Compared to the previous release which had a magnitude limit of Ks = 11.25, this fainter magnitude limit allows us to sample more distant parts of the local Universe, like the Shapley Supercluster. For our best χ2 fit value of β = 0.4, the amplitude of the Local Group (LG) dipole is lower than but consistent with the LG velocity inferred from the CMB at the 2σ level.

2012 Mar 02


Tanya Urrutia


Feedback in action in luminous, young, dust-reddened QSOs

Quasar feedback has long been invoked as the mechanism to exert 'negative' influence on kpc to Mpc scales to curtail star formation in its host galaxy, and/or further accretion onto the Supermassive Black Hole itself. Quasar mode feedback has recently become a heavily studied topic, due to the realization that it may play a fundamental role in the assembly history of galaxies. I will present evidence for quasar mode feedback via line driven winds in samples of dust reddened Low Ionization Broad Absorption quasars. These quasars are accreting at very high efficiencies and thus are very bright in the infrared. They are much more common at z > 0.5 than originally thought, by up to a factor of ten due to the obscuration in the optical and UV and the suppression of the emission lines typically found in quasars. Finally, I will present an outlook on possible future observations for these objects.

2012 Feb 27


Special Seminar: Andreas Faltenbacher

(Cape Town)

Anisotropy in the matter distribution at very large scales

Tracing the cosmic evolution of the Baryonic Acoustic Oscillation (BAO) scale with galaxy two point correlation functions is currently the most promising approach to detect dark energy at early times. A number of ongoing and future experiments will measure the BAO peak with unprecedented accuracy. N-body simulations indicate that the matter distribution is anisotropic out to ~150 Mpc, far beyond the BAO scale of about 100 Mpc. I will discuss implications for the measurement of the BAO.

2012 Feb 24


Benedetta Ciardi

(MPA Garching)

Cosmic reionization: theoretical modelling and challenging observations

In this presentation I will talk about the major phase transition experienced by the intergalactic medium commonly referred to as the reionization process. I will describe some recent theoretical modelling of this process and how the new generation of radio facilities, in particular LOFAR, will be able to provide unprecedented insight into it.

2012 Feb 20


Special Seminar: Stefano Ansoldi

(Udine University)

A statistical approach to the determination of model parameters in astrophysics: The case of active galactic nuclei synchrotron-self compton models

We present the details of a recent statistical study in which parameters for Active Galactic Nuclei one zone Synchrotron-Self Compton (SSC) models have been determined by statistically rigorous fits of simultaneous multiwavelength datasets. Guided by this example we will see how, improving over common eye-ball fits, results obtained with a full-fledged chi squared minimization procedure already suggest that existing observations might require improvements to some one-zone SSC models.

2012 Feb 10


Juan Carlos Munoz-Cuartas


Properties of the distribution of dark matter

In the standard cosmological paradigm, dark matter contributes with the second major fraction of the mass content of the universe. As such, it has important implications in the dynamics of the universe as well as in the process of formation of structures and galaxies. We study the properties of the distribution of dark matter at different scales: in dark matter halos, around dark matter halos and in the large scale structure. We study the distribution of mass in dark matter halos and focus most of our attention on the concentration parameter. We show how we interpret its mass and redshift dependence in terms of the growth of the halo. We discuss a novel feature of the concentration parameter at early times in the formation of halos, who tend to have higher concentrations than expected. We also study the distribution of mass around dark matter halos in a broad range of masses and redshifts. We provide an accurate fitting function for the full density distribution extending up to ~20 times the virial radius. In conjunction with the identification of galaxy groups and halos in the SDSS, this results allow us to build reconstructions of the cosmic mass density field with interesting features that allow a detailed study of environments in the large scale structure. We present the features of this method of reconstruction and discuss some of its applications.


2012 Jan 20


Sadegh Khochfar


The formation of massive galaxies through cosmic time

In my talk I will present results from LCDM simulations and SAMs on the various different stages that massive galaxies go through on their way to maturity: At high redshifts z~6 they go through a growth spurting phase driven by high gas accretion rates and possibly triggered star formation. This episode is followed by a period in time around z~2 when massive galaxies grow in 'equilibrium' with their cold accretion rates, before they turn to a phase of growth mostly via mergers. I will highlight each of these phases and discuss their consequences on the properties of galaxies.

2012 Jan 13


Hans-Erich Froehlich


Bayesian photometric spot modeling - experiences and first results

After a brief introduction into the Bayesian approach to model selection and parameter estimation, examples are presented: a 4-spot model for the CoRoT CP2 target star HD 50773 and a 7-spot model for the rapid rotator KIC 8429280, a cool (K2V) star with strong differential surface rotation.

2011 Dec 16 10:30 David Radburn-Smith
(University of Washington)

The GHOSTS Survey: Probing the Outskirts of Disk Galaxies

The GHOSTS (Galaxy Halos, Outer disks, Substructure, Thick disks and Star clusters) survey is the largest study of the resolved stellar populations in the outskirts of disk galaxies to date. The sample currently consists of 16 nearby disk galaxies, whose outer disks and halos are imaged with the Hubble Space Telescope. By combining these observations with high-resolution N-body simulations, we are exploring the assembly of disk galaxies and their ongoing evolution. Here I highlight a few of these comparisons, in particular: halo structure, stellar radial migrations, and cold-gas accretion.

2011 Dec 14 13:30 Fabio Zandanel
(Instituto de Astrofísica de Andalucía, CSIC)

The MultiDark Multi-Frequency Galaxy Cluster Mock Catalog

Using the observed X-ray properties of galaxy clusters we have implemented a phenomenological model to assign to each cluster in the MultiDark N-body simulation a gas density profile using only its dark matter halo mass. In this way, we have created a large galaxy cluster mock catalog, with more than 10,000 clusters above 1e14 Msun/h, that displays the observed X-ray luminosity-mass relation and luminosity function. We then compute the diffuse synchrotron radio emission coming from hadronic cosmic-ray interactions with the ambient gas in order to investigate the radio halo scaling relations and luminosity function. This mock catalog can be used for various science projects related with upcoming experiments such as LOFAR, eROSITA and CTA

2011 Dec 09 10:30 Pier-Emmanuel Tremblay
(LSW, Heidelberg)

The high-mass problem in cool white dwarfs: an old obstacle now seen with 3D radiation-hydrodynamics

White dwarfs with hydrogen-rich atmospheres are the most abundant of all degenerate objects. Their atmospheres are thought to be relatively simple, with a pure composition due to the gravitational settling, and can be used as spectroscopic standards. However, at cool effective temperatures (cooling age > 1 Gyr), a problem observed for the last 20 years is an unexpected 20% increase of the mean mass. We have recently improved our knowledge of these cool objects, with high-resolution observations to constrain the abundances of elements other than hydrogen, and with a better account of the non-ideal gas microphysics. Finally, we improved the macrophysics aspect of the models by using 3D radiation-hydrodynamics instead of the standard 1D models for the treatment of convective motions. This new generation of pure hydrogen models with small atmospheric convective zones could serve as a benchmark to study pulsation-convection interactions (in ZZ Ceti pulsating white dwarfs) and the influence of magnetic fields.

2011 Dec 02 10:30 Erik Johansson

Interaction of supernova remnants with interstellar clouds

Shocks are believed to be an indirect cause of star formation by triggering the collapse of interstellar clouds. Therefore, we consider clouds interacting with supernova remnants (SNR) and whether they can reach Jeans instability. We study this by the means of MHD simulations and are, to our knowledge, the first to simultaneously incorporate magnetic fields, radiative cooling/heating and anisotropic heat conduction in 3D at sufficient resolution for this problem. We go through some of the inherent intricasies of the problem and tentative results.

2011 Nov 11 10:30 Rene Heller

White dwarf - main-sequence star binaries from the Sloan Digital Sky Survey

Since the advent of the the Sloan Digital Sky Survey (SDSS), originally targeted at quasi-stellar objects, the number of white dwarfs (WDs) with physically bound main-sequence star companions (mostly dM stars) has increased radically, allowing for fundamentally new insights into stellar physics. I will briefly review the main concerns of WD-dM evolution as well as recent developments in the field and I will give an insight in my related work.

2011 Nov 02 11:00 Hyun-Jin Bae
(Yonsei University, South Korea)


2011 Oct 21 10:30 Ugur Ural

Constraining dSph masses in the presence of tides

Dwarf spheroidal galaxies (dSphs) are nearby laboratories to study galactic interactions and the dark matter content of individual galaxies. I will present a Markov Chain Monte Carlo based method for studying the dynamics of dwarf spheroidal galaxies in the presence of galactic tides. Using different dark matter halo profiles to model the initial state of the dSph and running a large number of mid-resolution N-body simulations, the method is designed to find the best models in the parameter space and constrain the total mass of the galaxy. I will use Carina dSph as a case study and show the constraints that can be obtained on its mass with the currently available data.

2011 Oct 14 10:30 Bernd Husemann

The AGN-host galaxy connection - New insights from the extended ionised gas

Active galactic nuclei (AGN) are nowadays thought to play an important role in the evolution of galaxies. Feedback from AGN has often been invoked to quench star formation in their host galaxies as well as to explain the tight scaling relation between black hole mass and bulge properties. However, observational evidence for the AGN feedback process and constrains for the AGN triggering mechanisms itself are still missing to uncover the intimate AGN-host galaxy connection. We present optical 3D spectroscopy for a large sample of 50 unobscured luminous QSOs at z<0.3. This sample allows us to study the properties of the surrounding extended ionised gas in unprecedented detail. Our results indicate that low-power radio jets have a significant impact on the extended ionised gas properties, but galaxy wide AGN-driven winds appear to be infrequent. Furthermore, we explore the gas-phase metallicity as a diagnostic tool to understand how AGN activity is connected to galaxy interactions. In this respect, we discovered a very interesting QSO host galaxy which exhibits an extraordinary low gas-phase metallicity and a significant offset from the scaling relations. Considering the strong evidence for the accretion of almost pristine gas from the environment makes this QSO a unique probe to study the AGN-host galaxy connection.

2011 Oct 07 10:30 Gerald Handler
(Nicolaus Copernicus Astronomical Center, Warsaw)

The Kepler mission - a revolution in asteroseismology

Designed for the search for earth-like planets in the habitable zone, the Kepler mission is by far the most sensitive photometry tool to date. Kepler devotes a small percentage of its observing time to asteroseismology, the sounding of the interior structure of stars by using pulsations as seismic waves. This talks reviews the first asteroseismic results of Kepler, including detections and interpretations of solar-like oscillations in hundreds of main sequence stars, in thousands of giants, in the field and in open clusters. New results on "classical" pulsators are presented and discussed, including hybridicity, i.e. the presence of different sets of oscillation spectra in the same star, including the first detection of solar-like oscillations in a Delta Scuti star. Finally, pulsations in evolved stars such as B subdwarfs, but also in binaries, up to relativistic effects in eclipsing binary light curves are discussed.

2011 Oct 05 14:00 Karin Muglach
(Artep/ NASA Goddard Space Flight Center)

New Insights Into the Structure of the Solar Chromosphere

2011 Sep 30 10:30 Erik Hoeg
(Niels Bohr Institut, Kopenhagen)

Astrometry lost and regained: From a modest experiment in Copenhagen in 1925 to the Hipparcos and Gaia space missions

Technological and scientific developments during the past century made astrophysics flourish, and resulted in our present deep understanding of the whole Universe. But this brought astrometry almost to extinction because it was considered to be dull and old-fashioned, especially by young astronomers. However, astrometric data still are of great scientific and practical importance for the investigation of celestial phenomena. The main subject of this talk is the development of astrometry during the 20th century which made astrometry flourish again through the success of the Hipparcos astrometric satellite, soon to be followed by the even more powerful Gaia mission. The Hipparcos mission, approved in 1980, was based on photoelectric detectors measuring one star at a time. In 1992 CCD detectors were introduced in the Roemer mission proposal which could measure ten thousands of stars simultaneously. During 1993-97 an interferometric mission option was also studied, but the Roemer option with direct imaging on CCDs is used in the actual Gaia mission.

2011 Sep 26 14:00 Alexander Kashlinsky
(NASA Goddard Space Flight Center)

Measuring the large scale bulk flow of galaxy clusters from CMB and X-ray data

In standard cosmological paradigm, large-scale peculiar velocities arise from gravitational instability due to mass inhomogeneities seeded during inflationary expansion. On sufficiently large scales, > 100 Mpc, this leads to a robust prediction of the amplitude and coherence length of these velocities independently of cosmological parameters or evolution of the Universe. For clusters of galaxies, their peculiar velocities can be measured from the kinematic component of the Sunyaev-Zeldovich (SZ) effect produced by Compton scattering of cosmic microwave background (CMB) photons off the hot intracluster gas. I will discuss results from new measurements of the large scale peculiar flows using a large X-ray cluster catalog and all-sky CMB maps from the WMAP satellite. The results cast doubt that the gravitational instability from the observed mass distribution is the sole - or even dominant - cause of the detected motions. Instead it appears that the flow extends across the observable Universe and may be indicative of the primeval pre-inflationary structure of space-time and its landscape.

2011 Sep 23 10:30 Andreas Schulze

Demographics of supermassive black holes

Supermassive black holes (SMBHs) and their cosmic growth are fundamental components of galaxies. They are essential for our understanding of galaxy evolution, as indicated by the tight relation between the masses of SMBHs and the properties of the galaxies spheroid component. Understanding black hole growth requires a census of the black hole population. We employed the Hamburg/ESO Survey to obtain such a census for the local population of active SMBHs, observable as type 1 AGN. We present results for the local AGN luminosity function and a novel approach for the determination of the underlying distribution functions, the active black hole mass function and the distribution function of the accretion rates. These results reveal evidence for ``AGN downsizing''. In the second part of the talk I will focus on the prospects to observationally determine cosmic evolution in the black hole-bulge relations using AGN samples. In particular, I will discuss the issue of selection effects and corresponding sources of bias on the results obtained from these studies. Applying our framework to literature studies, no statistically significant evidence for evolution in the black hole-bulge relations is found.

2011 Sep 09 10:30 Saleem Zaroubi
(University of Groningen)

The End of the Universe's Dark Ages

The Epoch of Reionization, which marks the end of the Universe's "Dark Ages", is one of the least explored epochs in cosmic evolution. During this epoch, the all-pervasive cosmic gas transforms from neutral to ionized. The Epoch of Reionization is thought to be caused by the first astrophysical sources of radiation and its study is crucial to our understanding of the physics of these sources and how they influenced the formation of later generations of astrophysical objects. To explore this pivotal epoch a number of radio telescopes are being build or designed (LOFAR, MWA, 21CMA, SKA) to observe the 21-cm hyperfine emission line of neutral hydrogen from the intergalactic medium during cosmic reionization. In this talk I'll review our current understanding of this epoch and describe how it will be observed with Radio telescopes and what we hope to learn from it.

You can download the talk here (pdf, 16 MB).

2011 Sep 02 10:30 Sebastian Nuza


2011 Aug 26 10:30 Mudit K. Srivastava

Imaging Characteristics of Ultra-Violet Imaging Telescope (UVIT) through Numerical Simulations

Ultra-Violet Imaging Telescope (UVIT) is one of the 5 payloads aboard the Indian Space Research Organization (ISRO)'s ASTROSAT Space mission, to be launched in near future. The science objectives are broad, extending from studies of individual hot stars, star-forming regions, interacting galaxies, active galactic nuclei, and cosmology. Imaging performance of UVIT would depend on several factors in addition to the optics, e.g. resolution of the detectors, Satellite Drift and Jitter, image frame acquisition rate, sky background, source intensity etc. Intensified CMOS-imager based photon counting detectors in UVIT put their own complexity over the reconstruction of the images. All these factors could lead to several systematic effects in the reconstructed images. Numerical simulations show that various parameters of photon counting detectors and related centroid algorithms would be playing a critical role in determining the imaging characteristics of UVIT. Our results show that reconstructed images from UVIT would suffer from the photometric non-linearity in a complex way. Further the angular resolution, photometric accuracy and non-linearity would depend on the values of various thresholds parameters chosen to detect photons. A thorough understanding of the functioning of the instrument is thus necessary to optimize the UVIT performance for its various scientific objectives.

2011 Aug 19 10:30 Steffen Heß

VPH - A new method to simulate hydrodynamics in cosmological environments

Lagrangian Voronoi particle hydrodynamics (VPH) is a new fluid particle model whose density estimate is carried out with the help of an auxiliary mesh constructed as the Voronoi tessellation. This approach provides higher effective resolution and is capable to represent sharp contact discontinuities. This makes the VPH scheme ideal to study phenomena that involve sharp density gradients. For instance galaxy-ICM interaction is one situation where numerical comparison studies have shown disagreements depending on the particular numerical method employed.

2011 Jul 22 10:30 Edward L. Chapin
(UBC Vancouver)

Recent advances in extragalactic submillimetre astronomy: Herschel and beyond

I will give a general introduction to galaxy formation and evolution studies using submillimetre surveys, ranging from ground-based observationss with SCUBA and MAMBO at ~1mm, to the Balloon-borne Large Aperture Submillimeter Telescope (BLAST), a 2-m precursor to Herschel which flew a prototype of the SPIRE camera (250--500um). I will then present some recent Herschel results, with an emphasis on the Herschel Multi-tiered Extragalactic Survey (HerMES), which is one of the largest coordinated surveys with the instrument. I will also try to touch on some of the major issues that we still face, and how they will be resolved with forthcoming instruments, such as ALMA, so-called "redshift receivers", SCUBA-2 and future space missions.

2011 Jul 15 10:30 Jaime Forero


2011 Jul 08 10:30 Anupam Mazumdar
(Lancaster University)

Origin of inflation

Primordial inflation is responsible for creating all matter and perturbations for the cosmic microwave background radiation, and seeds initial conditions for the large scale structures in the universe. In spite of the current experimental advancements, the origin of inflation is still poorly understood. In this talk I will focus on the origin of inflation and illustrate how to probe the inflaton candidate at terrestrial based experiments ranging from table top to the Large Hadronic Collider.

2011 Jul 04 11:00 Todor Kondic

Shear-Hall Instability and the Newborn Neutron Stars

Neutron stars are born differentially rotating and with very strong magnetic fields. As it is already known that there are instabilities related to the Hall effect which are powered by the shear flow, the question that naturally arises is about their significance for the formation of magnetic field of proto-neutron stars. We investigate the linearised Hall-MHD system to obtain the dominant eigenmodes and the associated growth rates. We find that the process amplifies the field on the timescales comparable to the rotation period, sufficiently fast to fully exploit the differential rotation which lasts for only hundred seconds.

2011 Jul 01 10:30 Rolf Peter Kudritzki
(Institute for Astronomy, University of Hawaii)

Stellar Spectroscopy Unleashed - ELTs and Red Supergiants in the Coma Cluster

The determination of the chemical composition and distances of galaxies is crucial for constraining the theory of galaxy formation and evolution in a dark energy and cold dark matter dominated universe. However, the standard techniques to obtain information about the chemical composition and distances of star forming galaxies are subject to large systematic uncertainties which are poorly understood.

As an alternative, I introduce a new method, which will use low resolution J-band spectroscopy of individual red supergiant stars (RSGs) in distant galaxies. Using Mauna Kea IRTF SpeX low resolution spectra of Milky Way RSGs and MARCS model atmospheres we have demonstrated that our analysis method allows individual metallicities and alpha/Fe ratios to be determined with an accuracy of about 0.1 dex (Davies, Kudritzki, Figer, 2010, MNRAS 407, 1203). The extension of the method to star forming galaxies beyond the Local Group with MOS devices at large telescopes such as MOSFIRE/Keck and KMOS/VLT is straightforward.

This new method will gain tremendous momentum with the next generation of ELTs and AO supported MOS instruments like IRMS at the TMT and EAGLE at the E-ELT, since the limiting magnitude in the diffraction limit case increases with the fourth power of the telescope diameter. We have shown that we can reach individual RSGs in galaxies as distant as the Coma Cluster (Evans, Davies, Kudritzki et al., 2011, A&A 527, 50).

I will also discuss the potential of observing the integrated light of Super Star Clusters (SSCs). The J-band light of these objects is entirely dominated by RSGs as soon as the cluster age is larger than 8 Myr (Gazak, Kudritzki, Davies, 2011, in prep.). This allows for the determination of accurate detailed chemical composition by simple population synthesis techniques. Because of the enormous brightness of SSCs in the J-band an enormous volume of the local universe can be studied in this way.

2011 Jun 28 11:00 Pierre Ocvirk
(Observatoire Astronomique de Strasbourg)

A signature of the internal reionisation of the Milky Way?

I will present a new semi-analytical model of the population of satellite galaxies of the Milky Way, aimed at estimating the effect of the geometry of reionisation at galaxy scale on the properties of the satellites. In this model reionisation can be either: (A) externally-driven and uniform, or (B) internally-driven, by the most massive progenitor of the Milky-Way. In the latter scenario the propagation of the ionisation front and photon dilution introduce a delay in the photo-evaporation of the outer satellites’ gas with respect to the inner satellites. As a consequence, outer satellites experience a longer period of star formation than those in the inner halo. We use simple models to account for star formation, the propagation of the ionisation front, photo- evaporation and observational biases. Both scenarios yield a model satellite population that matches the observed luminosity function and mass-to-light ratios. However, the predicted population for scenario (B) is significantly more extended spatially than for scenario (A), by about 0.3 dex in distance, resulting in a much better match to the observations. The survival of the signature left by the local UV field during reionisation on the radial distribution of satellites makes it a promising tool for studying the reionisation epoch at galaxy scale in the Milky Way and nearby galaxies resolved in stars with forthcoming large surveys.

2011 Jun 24 10:30 Beate Stelzer

X-ray emission from late-type stars: magnetic activity, accretion and outflows

The high-energy emission from stars is likely a key factor in the star and planet formation process. It irradiates circumstellar disks and planetary atmospheres and possibly induces their photo-evaporation. This central role in such major astrophysical processes lends importance to a good the understanding of stellar X-ray emission.

The bulk of X-ray emission from late-type stars is ascribed to plasma closed in coronal loops and heated by dynamo-generated magnetic fields. However, the solar-type dynamo mechanism is expected to break down at the borderline where stars become fully radiative (intermediate-mass stars) or fully convective (very-low mass stars and brown dwarfs). This supposedly affects the manifestations of magnetic activity and their relation with rotation rate, another crucial parameter for dynamo action.

To complicate the picture, additional processes may produce X-rays in young stars during the pre-main sequence phase: accretion and outflows.

I present a summary of our current knowledge about the X-ray characteristics of late-type stars, including studies of the influence of stellar X-rays on their circumstellar environment.

2011 Jun 22 11:00 A. Pawlik
(U Texas)

The sources of reionization

The reionization of the Universe, that is the transformation of the cosmic hydrogen from its initial neutral to its present highly ionized state a few hundred million years after the Big Bang, is a watershed event in the history of the formation and evolution of galaxies. In the next few years, upcoming telescopes such as the Low Frequency Array and the James Webb Space Telescopes will enable, for the first time, to directly probe galaxy formation during reionization and allow to address many of the open question that define the current frontier of the field. The perhaps single most important question concerns the nature of the sources that reionized the Universe. Present observations of high-redshift galaxies may already hold the answer to this question, but their interpretation is complicated by uncertainties in the rates at which the interstellar and intergalactic gas recombine. Cosmological simulations of galaxy formation and reionization are powerful tools for constraining these and other key quantities. In this talk I will present results from both large-scale cosmological simulations of reionization and zoomed cosmological simulations of the assembly of the first galaxies to investigate the role and nature of galaxy formation during reionization. I will discuss current constraints on the capability of observed galaxies to reionize the Universe.

2011 Jun 10 10:30 Bernard Schutz


The first gravitational wave mission in space will open up the low-frequency window for gravitational waves, around 1 mHz. This is one of the richest regions for expected signals, both from stellar binaries in the Galaxy and from massive black holes in distant galaxies. I will review the sources and what we can expect to learn from observations, not only about fundamental physics but also about cosmology, structure formation, galaxy centers, and stellar evolution. The long-standing LISA mission proposal is now being redesigned to fit into a tighter funding envelope, and I will report on the progress so far, and suggest what capabilities a redesigned mission might be able to deliver.

2011 May 27 10:30 Maneenate Wechakama

Dark matter pressure and multi-wavelength constraints on dark matter annihilation

Although cosmological observations suggest that a significant part of our Universe consists of non-baryonic cold dark matter, its exact nature of dark matter remains a mystery. A promising approach to address this problem relies on the possibility that dark matter particles annihilates with low probability into observable, standard model particles. Thus one can aim for indirect dark matter detection by looking for signatures of the annihilation products. In this talk, we will first discuss the contribution of dark matter annihilation to the interstellar gas pressure and consider the possibility that it has an effect on the rotation curve of spiral galaxies. We will then introduce constrains on dark matter annihilation based on recent muti-wavelength data.

2011 May 16 15:30 Martin Muehlegger
(MPE, Garching)

Simulated Observations of Galaxy Clusters for the XMM-Newton Distant Cluster Project

The XMM-Newton Distant Cluster Project (XDCP) is a serendipitous cluster survey using archival data of the XMM-Newton observatory. Its goal is the detection of high redshift galaxy clusters (z >~ 0.8). In order to make use of the project for cosmological applications, a crucial ingredient is the selection function of the survey, i.e. the cluster detection probability depending on various cluster parameters. For this purpose an XMM image simulator has been developed, which adds simulated clusters to real observations, taking into account instrumental effects. The employed cluster model is the beta-model with core radius and number of photons as model parameters and off-axis angle as an additional observational parameter. The simulated images were analyzed by the same procedure as the real data. From a first simulation run of 2.5 months on 20 CPUs, a subsample of 160 out of the 469 XDCP fields could be characterized with respect to the cluster detection probability depending on those three parameters. With suitable assumptions on the core radius distribution at high redshifts, the flux limit dependent survey sky coverage was derived for the subsample. The simulation pipeline is currently running on an MPE based workstation to complete the simulation run of 469 XDCP fields. I will report on the current project status and discuss future plans.

2011 May 13 10:30 Wolfgang Kalkofen
(Harvard-Smithsonian, Center for Astrophysics)

Does a Nonmagnetic Solar Chromosphere Exist?

The structure of the nonmagnetic solar chromosphere was investigated by Carlsson & Stein in a 1995 paper titled "Does a Nonmagnetic Solar Chromosphere Exist?" They concluded that a traditional chromosphere, where the kinetic temperature rises monotonically in the upward direction, does not exist. We question this conclusion.
We analyze observations from space (SUMER and Sunrise) and from the ground to establish observational criteria on temperatures, their gradients, and amplitudes of temperature fluctuations that must be satisfied by models of the quiet solar atmosphere.
We find that all modern three-dimensional, theoretical, acoustic-wave models have time-averaged chromospheric temperatures that decrease with height, contrary to observations, as well as temperature fluctuations that have much larger amplitudes than are observed. Among the predictions of the wave models is that hot, chromospheric radiation arises only as intermittent emission during hot phases of temperature fluctuations, and that the solar metal abundances must be significantly lower than those established with the empirical Holweger-Mueller model. The new abundances destroy the agreement that existed between acoustic modes predicted by empirical models for the old, higher abundances, and 10^5 observed eigenmodes of acoustic oscillations in the solar interior.
Our analysis shows that the temperature fluctuations in the nonmagnetic Sun have low amplitude, and that reducing the solar metal abundances to agree with the dynamical models is not justified.

2011 May 06 10:30 Rolf Chini
(Ruhr-Universität Bochum)

Most high-mass stars are born as twins

The formation of stars above about twenty solar masses and their apparently high multiplicity remain heavily debated subjects among theorists. We have performed a vast high-resolution radial velocity spectroscopic survey of about 250 O- and 360 B-type stars in the southern Milky Way which indicates that the majority of stars (> 85%) with masses above 16 solar masses form close binary systems while this fraction rapidly drops to 20% for stars of 3 solar masses. The binary fractions among different environment classes are: clusters (74%) associations (73%), field (48%), and runaways (75%). The high frequency of close pairs with components of similar mass argues in favour of a multiplicity originating from the formation process rather than from a tidal capture in a dense cluster. The high binary frequency of runaway stars that we found in our survey (75% compared to 25% in previous surveys) points to the importance of ejection from young clusters and thus supports the competitive accretion scenario.

2011 Apr 28 11:00 Nicolas Bernal
(Theory Department Physikalisches Institut Universitaet Bonn)

Constraining the Milky Way Dark Matter Density Profile with Gamma-Rays with Fermi-LAT

We study the abilities of the Fermi-LAT instrument on board of the Fermi mission to simultaneously constrain the Milky Way dark matter density profile and some dark matter particle properties, as annihilation cross section, mass and branching ratio into dominant annihilation channels. A single dark matter density profile is commonly assumed to determine the capabilities of gamma-ray experiments to extract dark matter properties or to set limits on them. However, our knowledge of the Milky Way halo is far from perfect, and thus in general, the obtained results are too optimistic. Here, we study the effect these astrophysical uncertainties would have on the determination of dark matter particle properties and conversely, we show how gamma-ray searches could also be used to learn about the structure of the Milky Way halo, as a complementary tool to other type of observational data that study the gravitational effect caused by the presence of dark matter. In addition, we also show how these results would improve if external information on the annihilation cross section and on the local dark matter density were included and compare our results with the predictions from numerical simulations.

2011 Apr 26 11:00 Melissa Ness

The Formation of the Galactic Bulge of the Milky Way

I will present the results to date of our spectroscopic survey of the galactic bulge of the Milky Way. Our aim is to understand the formation of the bulge and to determine if it formed via mergers, as predicted by CDM theory, or from disk instabilities, as suggested by its boxy shape, or both.
We are observing about 28,000 stars in fields in the bulge and out into the thin and thick disks, that span a longitude of ± 20 degrees and latitude of -5 to -10 degrees, targeting mostly clump giants. Our medium resolution AAOmega survey is measuring stellar velocities and chemical abundances. This will provide a quantitative test of which kind of bulge we have in our galaxy. The sample size is sufficient to detect a 5% merger generated bulge underlying an instability bulge. The survey extends out of the bulge into the surrounding thin and thick disk in order to evaluate the kinematical and chemical relationship between the bulge and adjacent disk from which it may have formed. The selection criteria for our stellar sample were chosen to include also the metal poor pre-galactic first stars which are expected now to be concentrated in the bulge region.
We have almost concluded observations and are analysing data from our 25,000 stars observed to date. We have determined the rotation curve for the bulge as well as the [Fe/H] and [alpha/H] for each star. Stellar parameters (Teff, logg, [Fe/H]) have been determined via a chi2 comparison between each spectra and a large grid of synthetic spectra and from this the true bulge candidates have been identified. From this information we report on metallicity gradients in the bulge and confirm a relationship between rotation velocity and metallicity, identifying a slowly rotating metal poor component in the inner bulge. The ongoing results from this data set will ultimately be compared with N-body models in order to evaluate and interpret these findings which I will present.

2011 Apr 8 10:30 Cristina Chiappini

Spinstars: the first polluters of the Universe?

The chemical enrichment of the Universe in elements heavier than helium (metals) started as early as 300 Myrs after the Big Bang, upon the death of the first massive stars. Although already dead, their chemical imprints can be observed today in very-metal-poor halo stars (with one-thousandth or less of the solar iron). I will show that we have reasons to believe that a large fraction of the massive stars in the early Universe were fast rotators (spinstars). So far the chemical signatures of spinstars had been found only in the MW halo. Recently we found the imprints of fast rotators also in the Bulge, for the first time, in its oldest globular cluster. In addition, we show that spinstars could have been important contributors to the s-process elements in the early Universe, with important consequences on our understanding of the cosmic chemical enrichment. Fast stellar rotation could have been a common property of stars in the Early Universe, and is now also supported by the latest hydrodynamic simulations of the formation of the first stars. The impact of an early generation of fast rotating stars is manifold and goes beyond chemistry, probably also playing a role in the re-ionization of the Universe.

2011 Apr 7 11:00 Robert Droulans
(CESR, Toulouse)

Unveiling the high energy emission of accreting compact objects with SPI/INTEGRAL

The study of the high energy emission (>20 keV) is essential for understanding the radiative processes inherent to accretion flows onto compact objects (black holes and neutron stars). The X/gamma-ray continuum of these systems is successfully interpreted in terms of two components. The first component corresponds to blackbody emission from a geometrically thin optically thick accretion disk while the second component is generally associated to Compton scattering of the thermal disk flux off hot electrons. Despite considerable advances throughout the years, the heating mechanisms as well as the structure of the Comptonizing medium remain poorly understood. In order to shed light on the physical processes that govern the innermost regions of the accretion flow, we take advantage of the data archive accumulated by the SPI instrument, a high energy spectrometer (20 keV - 8 MeV) developed at the CESR (now IRAP, Toulouse, France) for the INTEGRAL mission. Above 150 keV, SPI combines a unique spectral resolution with unequalled sensitivity, being thus an ideal tool to study the high energy emission of accreting compact objects.
At this seminar, I will present the results of timing and spectral studies of three particular systems. First, I adress the high energy emission of the enigmatic microquasar GRS 1915+105, a source characterized by colossal luminosity and strong chaotic variability in X-rays. On a timescale of about one day, the photon index of the 20 - 200 keV spectrum varies between 2.7 and 3.5 ; at higher energies (>150 keV), SPI unveils the systematic presence of an additional emission component, extending without folding energy up to ~500 keV. Second, I address the high energy emission of GX 339-4, a source whose spectral properties are representative of black hole transients. The spectrum of the luminous hard state of this source shows a variable high energy tail (>150 keV), with significant flux changes on a short timescale (several hours). I explain the observed spectral variability in the framework of a new Comptonization model which self-consistently accounts for the presence of a magnetic field and introduce a purely non-thermal scenario as an alternative interpretation of the luminous hard state of accreting black hole binaries. Finally, I present a long term study of the high energy emission of the X-ray burster GS 1826-24. The accretion flow being extraordinarily stable, I integrated over 8 Msec of data allowing to measure the average source spectrum up to 500 keV. Once again, I find strong evidence for a hard spectral tail above 150 keV, establishing that this feature is not exclusively associated to black hole systems. I compare the results obtained for the three sources and discuss the possible physical origins of the high energy emission of stellar-size compact objects, showing that all observed spectral shapes can be explained by a non-thermal magnetized corona model.

2011 Mar 30 11:00 Joachim Trümper
(MPE Garching)

What powers the Quiescent Emission of Anomalous X-ray Pulsars and Soft Gamma-ray Repeaters - Magnetic field decay or Accretion?

2011 Mar 25 10:30 Fabio Iocco

Dark Matter and Stars (aka 'DarkStars')

If Dark Matter (DM) is composed of Weakly Interacting Massive Particles (WIMPs), it can affect the properties of stars. In the local Universe effects are feeble, nonetheless they can in principle be used in order to set constraints on the nature of DM particles with observations of the Sun, and of compact objects at the Galactic Center, in Globular Clusters and in White Dwarf Galaxies. The first generation of stars to form (Population III) might have been affected in a more dramatic way from the effects of self-annihilating WIMP DM, and traces of this can be found in its properties. In the first part of my talk I will highlight the mechanism by which WIMPs can affect stars, and how local Universe can be used as laboratory for DM searches through stellar observables. I will devote the second part to draw a consistent picture of DM effects on the First Stars, from proto-stellar stages until stellar death.

2011 Mar 18 10:30 Pratika Dayal

Cosmic Lighthouses: the nature of high-redshift galaxies

We are in the golden age for the search for high-redshift galaxies. A specific class of such galaxies, the Lyman Alpha Emitters (LAEs) have rapidly been gaining popularity as probes of the epoch of reionization, galaxy evolution and the dust enrichment of early galaxies; a LAE has recently been confirmed at z=8.6, making it the farthest astrophysical object known. Coupling state of the art cosmological simulations with a physically motivated, self-consistent model for LAEs, we aim to put precious constraints on their elusive physical properties, build a bridge between the high-redshift and the local Universe (the Milky Way), gain insights on reionization and make predictions for future instruments such as the Atacama Large Millimeter Array (ALMA) and the James Webb Space Telescope (JWST).

2011 Mar 14 13:30 Ulrike Kuchner
(University of Vienna, Austria)

Intergral field spectroscopy of interacting Seyferts - Tracing accretion signatures with [OIII]/Hbeta ratios

Accretion of external material could significantly contribute to fuel the AGN in Seyfert galaxies. Such a process causes a negative metallicity gradient in the nuclear region of the galaxy. The talk introduces the possibility of decreasing metallicity gradients towards the center of interacting Sy1 UGC1935 and Sy2 Mrk607. Archive observations of VLT's VIMOS Integral Field Unit in high resolution were used to search for such features. [OIII]/Hbeta line ratios are measured as metallicity indicators throughout the central 27x27 arcsec**2 of the sample galaxies to look for accretion signatures.:w

2011 Feb 25 10:30 Jakob Walcher

The sociology, archeology and geography of galaxy evolution

Galaxies are beautiful objects. How did they come to be this way? Part of the answer to this question lies in understanding when, where and why their stars were made. I will discuss a number of observational studies that contribute to our understanding of the build-up of stellar mass and stellar structure in galaxies.

2011 Feb 18 10:30 Benoit Famaey
(OAS Strasbourg)

Stellar streaming motions and the non-axisymmetry of the Galaxy

We exhibit the observational effects of the non-axisymmetry of the Milky Way potential on stellar motions in the Sun's vicinity. Moving groups such as the Hyades and Sirius streams, containing stars of very different ages and chemical compositions, were until recently the best local dynamical tracers of the bar and spiral of the Milky Way. These tracers are also complemented by the observed non-zero value of the Oort constant C as determined from proper motions of red giants in the extended local disk. Here, we additionally report the recent detection of a radial velocity gradient in the inner disk, with RAVE line-of-sight velocities of more than 200 thousand stars limited to a distance of 2 kpc from the Sun. Further observational confirmation of this striking finding, e.g. with line-of-sight velocities of stars at lower latitudes and to larger distances, together with further modeling, should help better constrain the radial motion of the Local Standard of Rest, as well as the non-axisymmetric components of the Galactic potential, including the bar, the spiral arms and possibly the ellipticity of the dark halo.

2011 Feb 15 10:30 James Beletic
(Astronomy & Civil Space TELEDYNE Image Sensors)

The Fantastical World of Adaptive Optics

2011 Feb 03 15:30 Peter Gömöry
(Astronomical Institute of the Slovak Academy of Science, Tatranska Lomnica)

Spectropolarimetry of a Small-Scale Magnetic Loop Emergence

We investigated the temporal evolution of a magnetic flux emergence within a granule in the quiet-Sun internetwork at disk center. Combination of an IR spectropolarimetry of high angular resolution performed in two Fe i lines at 1565 nm with speckle-reconstructed G-band imaging was used for observations at the German Vacuum Tower Telescope. The magnetic field parameters were computed by a LTE inversion of the full Stokes vector using the SIR code. To interpret the observations, we created a geometrical model of a rising loop in 3D. We then synthesized spectra from the 3D model for a comparison to the observations. The observed event can be interpreted as a 12 min episode of a small-scale loop occurrence with a total magnetic flux of around 3 x 1017 Mx . The fast disappearance of the loop at the end could possibly be due to magnetic reconnection.

2011 Jan 28 10:30 Ivan Minchev

Numerical modeling of galactic disks: Non-equilibrium processes and implications to disk evolution

I will discuss the dynamical evolution of galactic disks resulting from internal instabilities such as central bars and spiral density waves. A simulated disk can show clumps and gaps in the local velocity distributions all over the galaxy. These gaps can be associated with both discontinuities in the spiral arm morphology, such as pitch angle variations or the appearance of armlets, and Lindblad resonances with the patterns of spiral and bar waves. Such features are ubiquitous because there are multiple coupled waves traveling through the disk. The coupling among multiple non-axisymmetric patterns can also have very strong effect on the disk morphology and chemical evolution. I will show that the stochastic radial migration and heating resulting from the resonance overlap of multiple patterns can flatten metallicity gradients, extend galactic disk profiles, and create thick disk components in both Milky-Way-size and low-mass systems. The timescale of all these processes is 1-2 Gyr, which is drastically shorter than previously expected and thus puts strong constraints on the longevity, strength and pattern speeds of the Milky Way bar and spiral structure.

2011 Jan 25 10:30 Joshua Adams
(Austin, Texas)

Two undesigned niches for VIRUS-P: measuring dark matter profiles in late-type galaxies and constraining the z=0 UV background

2011 Jan 20 10:30 Else Starkenburg

The satellites of the Milky Way: Insights from modeling and observations

2011 Jan 18 10:30 Guiseppina Battaglia
(ESO, Garching)

Probing galaxy evolution with Local Group dwarf galaxies

2011 Jan 14 10:30 Siegfried Franck
(Postdam Institut fuer Klimafolgeforschung (PIK))

The search for a second Earth - A geophysical perspective

2011 Jan 13 10:30 Sebastiano Cantalupo

The Bright Lyman-alpha Side of the Intergalactic Medium