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2012 Jan 13 10:30 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.

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

2010 Dec 17 10:30 Adrian Partl

Cosmological Radiative Transfer and the Ionization of the Intergalactic Medium

In recent years, observations of the intergalactic medium probed the ionisation history of the universe to higher and higher redshifts, approaching the era of reionisation. Latest technology radio telescopes such as LOFAR will soon constrain the universe's ionisation history up to the first UV producing objects that ended the dark ages.
Modelling of the end of the dark ages is made possible with state of the art 3D radiative transfer simulations. Using a Monte-Carlo code, we analysed the line of sight proximity effect near high redshift quasars. We studied the influence of various biases such as the quasar host environment, quasar spectral energy distribution and large scale structure on measurements of the ionizing background radiation. We applied refined analysis methods to study the large scale environmental bias on the proximity using high-resolution dark matter simulations. Our findings shed light on discrepancies in the observed ionized flux derived using the proximity effect or flux decrement statistics.

2010 Dec 13 13:00 Shy Genel
(MPE Garching)

Dark Matter Halos and z~2 Galaxies: Mergers, Smooth Accretion, and Feedback

In the LCDM model, both dark matter halos and galaxies form hierarchically by mergers but grow also via direct accretion of "smooth" material. I will describe the growth modes of dark matter halos as inferred from large cosmological N-body simulations. First, I will describe the merger rate of halos and then discuss the role of smooth, i.e. non-merger, accretion, which is found to be significant. Finally, I will present high-resolution, "zoom-in", cosmological SPH simulations that produce star-forming turbulent disks reminiscent of observed z~2 galaxies.

2010 Dec 10 10:30 Jochen Klar

A detailed view on filaments and sheets of the warm-hot intergalactic medium

Numerical simulations predict a considerable fraction of the missing baryons at redshift z < 0 resting in the so called warm-hot intergalactic medium (WHIM). The filaments and sheets of the WHIM have high temperatures (10^5-10^7 K) and a high degree of ionization while having only low to intermediate densities. Therefore their reliable detection is a challenging task for today's observational cosmology. The particular physical conditions of the WHIM structures, e.g. density and temperature profiles, velocity fields, are expected to leave their special imprint on spectroscopic observations. In order to get further insight on those conditions, we perform hydrodynamical simulations of the WHIM. Instead of analyzing large simulations of cosmological structure formation, we simulate particular well defined structures and study the impact of different physical processes as well as scale dependencies on those.

2010 Dec 03 10:30 Richard Parker

Star and Planet Formation: Constraints from Cluster Evolution

The effect of dynamical evolution in open star clusters may have profound implications for the formation of stars and planets. As most stars form in clusters, understanding the influence of cluster evolution is of fundamental importance. I will present results from N-body simulations of dynamical evolution in open clusters, demonstrating its effects on primordial binary systems (stellar and brown dwarf). I will extend these ideas to look at the probable effects of cluster evolution on planet formation. I will then briefly mention avenues for future work.

2010 Nov 26 10:30 Glenn van de Ven

Dynamics of galaxies and globular clusters unraveled with two-dimensional kinematics

Two-dimensional stellar kinematics obtained with the integral-field spectrograph SAURON allow the classification of early-type galaxies into 'slow' and 'fast' rotators, different from their morphological classification into ellipticals and lenticulars. Most fast rotators, including lenticular as well as many elliptical galaxies, are consistent with oblate axisymmetric disk-like systems. On the other hand, the slow-rotator ellipticals show clear deviations from axisymmetry, which can be modeled with our extension of Schwarzschild's orbit superposition method to triaxial geometry.
Besides galaxies, I show that Schwarzschild's method can also be used to model in detail globular clusters such as omega Cen and M15. The recovered internal orbital structure of omega Cen reveals besides a signature of tidal interaction, also a central stellar disk, supporting its origin as the nucleus of a stripped dwarf galaxy. The fromally best-fit Schwarzschild model for M15 includes an intermediate-mass black hole, but we cannot exclude a model in which dark renmants make up the dark mass in the collapsed core.

2010 Nov 19 10:30 Esteban Silva Villa
(Astronomical Institute Utrecht)

Constraining field star and star cluster formation histories in nearby galaxies. How do they relate?

A large fraction of a galaxy's history is encoded in its field stars and star clusters. Nevertheless, the link between these two populations is not fully understood. Even when it is commonly assumed that most stars formed in clusters, the fraction of star formation actually happening there is still uncertain. In this talk, I will present a systematic study over the galaxies NGC5236, NGC7793, NGC1313, NGC45, and NGC4395, where star clusters and field stars were analyzed separately. The results suggest that the ratio of star formation happening in clusters compared to the global one varies for each galaxy. Additionally, I will present constraints on how this variation is spatially distributed over the galaxies' spiral arms.

2010 Nov 12 10:30 Yehuda Hoffman
(Racah Inst. of Physics, Hebrew University, Jerusalem)

From Peculiar Velocities to Constrained Local Universe Simulations

Peculiar velocities of galaxies trace the distribution of matter in the universe, hence they provide an almost direct mapping of the dark matter. A Bayesian methodology, consisting the Wiener filter and constrained realizations of Gaussian fields, is used to reconstruct the large scale structure of the universe from incomplete, sparse and noisy catalogs of peculiar velocities. Two applications are to be presented: a. The structure of the universe on the scales of a few tens of Mpc; b. Constrained Local UniversE Simulations (CLUES) - the numerical approach to near field cosmology.

2010 Nov 11 15:30 Michael Demidov
(Institue for Solar-terrestrial Physics, Irkutsk, Russia)

On Multi-Line Spectro-polarimetric Diagnostics of the Quiet Sun's Magnetic Fields: Possibilities and Problems.

On the long way to establish the reliable physical properties of the solar atmosphere from different kinds of magnetic field measurements, a significant progress has been achieved, but there are many important issues which are still waiting for their solution. One of these is the question of the choice between various models with different parameters which can reproduce the available observable data almost equally well. This problem is especially essential for the interpretation of the weak magnetic fields of the quiet Sun that cover usually most of the solar surface, and practically the entire disk during periods of minimal activity. This problem hardly ever has a simple solution using only single spectral line observations, even if the full line profile is recorded in all Stokes parameters. Much more hope is justified for multi-spectral line spectro-polarimetric observations, especially if lines with very different properties are involved. In the present study, which covers the whole solar disk, high-precision Stokes-meter simultaneous observations in 15 different spectral lines in the vicinity of FeI 525.02 nm are analyzed with the SIR inversion code. It is demonstrated that application of the multi-line two-component approach allows to reach more-or-less determined conclusions concerning such parameters as filling factor, magnetic field strength, and temperature. However, it is shown that due to some restrictions in the SIR approach, there are some physical uncertainties in the interpretation of the obtained results. The importance of the next logical step - application of the 3D MHD simulations, is noticed finallyally.

2010 Nov 05 10:30 Bruce Balick
(Astronomy Department, University of Washington)

New Vistas on Planetary Nebulae

A series of very detailed theoretical papers by the numerical hydro group at Potsdam has set new and exciting challenges in observational astrophysics. The numerical models make a large set of theoretical predictions that can discriminate how PNe evolve from stars of a large range of initial masses and chemical compositions. Their models have been constrained by the usual data: emission-line images and ratios, extant observations of Doppler shifts, x-ray morphologies, and may other tracers that are sensitive to evolving stellar mass loss, age, etc. This talk is about entirely new sets of data, some already enabled by Hubble Space Telescope imaging. I shall present some of the new Hubble results being obtained from 15 years of observations using the WFPC2 camera that provide some very useful time derivatives of nebular structure and fluxes. I shall also outline what lies ahead as new tools for observational nebular exploration come on line in the next decade. These will probe the a variety of key properties of AGB stellar mass loss with far greater depth than possible now.

2010 Nov 04 11:00 Francisco-Shu Kitaura Joyanes
(Scuola Normale Superiore, Pisa)

Bayesian reconstruction of the cosmological large-scale structure

The Large-Scale Structure (LSS) in the Universe contains a wealth of Cosmological information. However, the observables which trace the LSS are plagued by many uncertainties. A careful treatment of the systematic errors together with a precise modeling of the underlying matter field is necessary. We present a Bayesian analysis of the Cosmological Large-Scale Structure with some applications to observational data.

2010 Nov 03 11:00 Dr. Martin Wendt
(Hamburger Sternwarte)

Variability of fundamental physical constants on cosmological scales - methods and shortcomings

The possible variation of the fundamental constants of nature is currently a very popular research topic and has a long history. Theories unifying gravity and other interactions suggest the possibility of spatial and temporal variation of physical 'constants' in the Universe. The variation of the dimensionless constants mu, the proton-to-electron mass ratio, and the finestructure constant alpha can be checked via quasar absorption line spectroscopy. However, current findings are partially contradictory and our intention is to asses the accuracy of the investigation concerning a possible variation of the fundamental physical constant mu and to provide more robust results. The goal in mind is to resolve the current controversy on variation and devise explanations for the different findings. The literally global effort to resolve these issues brought forth a large ESO observation program to obtain state-of-the-art UVES QSO spectra and to develop future-proof methods of analysis.

2010 Oct 22 10:30 Francisco Prada
(Instituto de Astrofisica de Andalucia (CSIC), Granada, Spain)

Gamma-ray dark matter searches

The nature of dark matter is still one of the most important open questions in modern physics. Many different candidates have been proposed as DM constituents, yet no detection has been reported. One of the most studied scenarios is that of SUSY dark matter particles, where gamma-rays are produced as secondary products of WIMP decay or annihilation. In this talk I will discuss recent gamma ray observations with Imaging Atmospheric Cherenkov Telescopes and prospects for detection with the Fermi satellite all-sky survey.

2010 Oct 15 10:30 Theresa Lüftinger
(Univ. Vienna)

The complex picture of Ap stars

Upper main sequence magnetic chemically peculiar (Ap) stars very often show inhomogenous chemical abundance distributions across their surface and with height in their atmospheres. Sophisticated techniques such as Doppler- and magnetic Doppler imaging make it possible to directly assess these inhomogeneous abundance structures and magnetic field geometries.
With the advent of highest quality photometric data obtained in space with Satellite missions like CoRoT, MOST, and Kepler, and using a Bayesian approach to star spot modeling, we have now the excellent possibility to combine outstanding photometric data with results from ground based spectroscopy and spectropolarimetry using, e.g., the NARVAL, HARPSpol, ESPaDOnS, and SemelPol spectropolarimeters.
In this talk, I will present recent results of our attempts to better understand the physics of the complex atmospheric structures in Ap stars based on studies of 3D chemical spot structures and results from photometric- and magnetic Doppler imaging using (full) Stokes vector spectropolarimetry and space photometry.

2010 Oct 08 10:30 Internal Scientific Committee (AIP) Institute Conference

2010 Oct 01 10:30 Petri Käpylä
(Univ. Helsinki)

Reynolds stress and turbulent heat transport in spherical shell convection

Differential rotation plays an important role in the dynamo process of stars. Current understanding is that differential rotation itself is caused by the interaction of anisotropic turbulence and global rotation. In mean-field theory these effects are described by the Reynolds stress and turbulent heat fluxes.
We compute the Reynolds stress and turbulent heat fluxes in spherical shell convection. The results are compared with earlier Cartesian simulations and analytical theories. We find that our results are in accordance with theory in the slow rotation regime but at odds with it for rapid rotation. The latitudinal heat flux is equatorwar for slow, and poleward for rapid, rotation.
The rotation profiles vary from anti-solar (slow equator) for slow and intermediate rotation to solar-like (fast equator) for rapid rotation. In the latter case, however, the profiles are dominated by the Taylor-Proudman balance.

2010 Sep 29 14:00 Sibylle Guenter
(Max-Planck-Institut fuer Plasmaphysik, Garching)

Plasma physics problems in magnetic fusion devices

2010 Sep 28 10:30 Jens Chluba
(CITA Toronto)

Signals from the Cosmological Recombination Epoch

The Planck Surveyor is currently measuring the CMB temperature and polarization anisotropies with unprecedented precision. For the analysis of these data sets it will be very important to understand the ionization history of the Universe at redshift z~1100 with very high accuracy, since otherwise uncertainties in the modelling of the recombination process may lead to significant biases in the deduced values of some cosmological parameters. In addition to the simple fact that free electrons are captured by protons and helium ions also some photons are released in the cosmological recombination process, leading to small distortions in the CMB blackbody spectrum which should still be present today. This recombination radiation carries valuable information about the dynamics of recombination and the underlying cosmological parameters, which until now has not been accessed. In my talk I will review some of the recent refinements in connection with the ionization history of the Universe and the CMB power spectra, showing that neglecting details in the physics of recombination will lead to important biases in the values of n_s and Omega_b. Furthermore, I will try to show that one could learn a lot about cosmological parameters, details in the recombination dynamics, energy release at high redshift and possible dark matter annihilations during recombination by directly measuring the cosmological recombination radiation.

2010 Sep 23 15:00 Matthew Browning
(CITA Toronto)

Rotation and magnetism in simulations of convective stars

2010 Sep 17 10:30 Kelly Foyle

Spiral Arms: How they Affect Angular Momentum Transfer and Star Formation

The formation of spiral arms has been studied at length. Few studies however have investigated how spiral structure can affect the observational properties of disk galaxies. In this talk I present some recent results on how spiral structure may affect the dynamical secular evolution of disk galaxies and star formation. I will present the first observational estimate of the torque-induced instantaneous angular momentum flow, resulting from non-axisymmetric features in the stellar distribution for a sample of 24 galaxies. The strongest torques were found among barred galaxies. In the inner regions, the average torques are strong enough to redistribute angular momentum on a timescale of ~4Gyr with an outward angular momentu flow. In examining the role of spiral arms in star formation I show that they do not dominate, even in grand-design spiral galaxies as there is a comparable amount of interarm star formation. Further, I show that the arms show no enhancement in the efficiency of star formation in terms of molecular gas. These results point to a spiral structure that plays a lesser role in shaping a galaxy's observable properties as was previously thought. The strength of gravitational torques depends more strongly on bars than on spiral structure, and spiral arms are not regions of enhanced star formation efficiency. At best they act to reorganize the interstellar medium and concentrate the gas.

2010 Sep 16 11:00 Guilhem Lavaux
(Johns Hopkins University)

Peculiar velocities of galaxies: reconstruction and re-simulation

A valuable source of information on the distribution of dark matter and the growth of structures lies in the peculiar velocity field of the galaxies. I present here a short review of peculiar velocity field reconstruction methods and in particular the more recently Monge-Ampere-Kantorovitch reconstruction method of galaxy trajectories. I then illustrate the use of orbit reconstruction in three contexts. First, I apply this method to recover peculiar velocities of galaxies to a real galaxy sample: the 2MASS Redshift survey. I compare the predicted peculiar velocities predicted from the distribution of galaxies to the observed peculiar velocities in our neighborhood of 30 Mpc/h. I study the origin of the motion of the Local Group relative to the Cosmic Microwave Background dipole. I discuss how these two studies may help at putting additional constraints on the Lambda CDM models. Second, I use the reconstructed peculiar velocities to produce a precise re-simulation of the dark matter distribution in the Local Universe. I discuss the method, the shortcomings and some of the applications of this simulation.

2010 Sep 15 13:30 Iris Traulsen
(Institut fuer Astrophysik Goettingen)

On the X-ray spectra of soft X-ray selected magnetic cataclysmic variables

Magnetic cataclysmic variables of AM Her type comprise an accreting white dwarf with a strong magnetic field. Under its influence, the accretion stream is channeled along the field lines towards the poles of the white dwarf, preventing the formation of an accretion disk and allowing for direct insight into the accretion regions. Due to the high temperatures developing in the accretion process, a considerable fraction of the total emission is found at X-ray energies: In the hard X-ray regime (E~0.5-10.0 keV), we see emission from the material which is decelerated above the white-dwarf surface; and in the soft X-ray and far ultraviolet regime (E< 0.5 keV), from the heated photosphere, where the hard emission is reprocessed. A significantly large group of AM Her systems have been found to emit mainly at X-ray energies below 0.5 keV. These systems could play an important role in interpreting the energy balance of polars. We perform dedicated XMM-Newton observations to study the spectral components and their flux contributions of several AM Her systems selected by their distinct soft X-ray fluxes. Modeling the spectral signature of these system components requires an approach to the complex temperature structure in accretion column and accretion region, which we approximate with multi-temperature white-dwarf and plasma models. I present the current status of our modeling and spectral analyses of three X-ray soft systems.

2010 Sep 10 10:30 Olaf Wucknitz
(AIfA Bonn)

LOFAR - a European VLBI-array for radio astronomy

The LOw Frequency ARray (LOFAR) is a new radio interferometry array that is currently being completed in the Netherlands and a couple of other countries. LOFAR covers the frequency range 10-270 MHz in which radio astronomy has started but which has been largely neglected since then. The stations outside of the Netherlands (currently four of them in Germany) are particularly important to reach sub-arcsec resolution and turn LOFAR into a true VLBI array. This talk gives an introduction into the principles of radio interferometry and LOFAR and shows some early successes with an emphasis on long-baseline, high-resolution work. LOFAR has already produced the first ever high-resolution images of the sky at wavelengths of several metres.

2010 Sep 09 15:00 Pia Zacharias
(KIS, Freiburg)

Spectral Analysis of three-dimensional MHD models of the solar corona -

A mass cycle between the chromosphere and the corona. Emission lines in the transition region and corona show persistent line shifts. It is a major challenge to understand the dynamics in the upper atmosphere and thus these line shifts, which are a signature of the mass cycle between the chromsophere and the corona. We examine EUV emission line profiles synthesized from a 3D MHD coronal model of a solar-like corona, in particular of an active region surrounded by strong chromospheric network. This allows us to investigate the physical processes leading to the line Doppler shifts, since we have access to both, the synthetic spectra and the physical parameters, i.e. magnetic field, temperature and density in the simulation box. By analyzing the evolution of the flows along field lines together with the changing magnetic structure we can investigate the mass cycle. We find evidence that loops are loaded with mass during a reconnection process, leading to upflows. After the loops disconnect from the reconnection site, they cool and drain which leads to the observed redshifts. Previous 1D loop models (neglecting the 3D nature) assumed that heating leads to evaporation and upflows followed by a cooling phase after the heating stops. The scenario modeled here is quite different, as it shows that the continuously changing three-dimensional magnetic structure is of pivotal importance to understand the mass balance between the chromosphere and the corona.

2010 Sep 07 14:00 Thomas Eisenbeiss
(AIU Jena)

Distances to Isolated Neutron Stars

With their soft and thermal X-ray emission isolated neutron stars are great laboratories to study the surface of neutron stars. The distance is one of the most fundamental quantities in astrophysics. The transition from observables (such as apparent diameter) to physical quantities (such as the physical radius) depends on the distance to some power. In this talk the redetermination of the distance of the two brightest isolated neutron stars is presented and compared with previous distance measurements. As an introduction a short overview of the so called ''Magnificent seven'' is given.

2010 Aug 27 10:30 Mudit K. Srivastava
(Inter University Centre for Astronomy and Astrophysics)

Pune, India

Design and Development of an Optical Fibre based Integral Field Unit (IFU) on IUCAA 2m Telescope Integral Field Spectroscopy has become a powerful tool for modern astronomical observations and Integral Field Units (IFUs) are the most popular tool to perform this. An optical fibre based Integral Field Unit (IFU) has been developed at Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune, India for IUCAA 2m telescope. It is based on the idea of connecting the focal plane of the telescope with the spectrograph slit using a fibre bundle with some coupling optics. In this way when an extended object is observed each fibre receives light coming from a particular region of the object. Each individual spectrum appears well separated on the detector; therefore, spatial information and spectral information are collected simultaneously. The IFU is being used as one of the modes of IUCAA Faint Object Spectrometer and Camera (IFOSC), an instrument mounted on the IUCAA 2m f/10 telescope at Girawali (near Pune). The IFU is optimized for the low resolution spectroscopy in visible spectrum and consists of 100 fibres with the field of view of 13 arc-second X 6 arc-second. Three different sky sampling scales of 1.0, 1.2, and 0.8 arc-seconds per fibre have been provided for different seeing conditions. The IFU has been commissioned successfully on the IUCAA telescope in the early 2010. In this talk, the speaker would describe the development of this IFU including its optical design, fabrication, commissioning tests and data characteristics.

2010 Jul 16 10:30 Catherine Fischer
(Univ. Utrecht)

Dynamics of solar magnetic fields

Magnetic field is present almost everywhere on the sun and occurs on all scales. It is known to be the cause of solar activity and is suspected to play an important role in the heating of the chromosphere and corona - a riddle that has fascinated solar physicists for decades. It is therefore important to obtain exact information on the solar magnetic field and to understand the interaction of convective forces and magnetic elements. It is only now that theoretically predicted small-scale mechanisms such as flux emergence and convective collapse events have been directly observed, thanks to the high cadence, high spatial resolution and high polarimetric sensitivity data from instruments as the Hinode satellite. Groundbased polarimeters, such as the SOLIS VSM, provide us with full Stokes profiles with high temporal resolution and deliver valuable information on magnetic field development and mass flows of complete active regions. I will give a short introduction to solar polarimetry and Stokes inversion techniques used to infer the magnetic field vector and will present a study of several quiet sun time series taken with the polarimeter (SP) on board Hinode. This data has been used to obtain statistics on convective collapse and flux cancelation events, processes that are important in the intensification of magnetic fields and in the removal of magnetic flux from the solar surface. A study of a time sequence of a flaring active region recorded by the SOLIS Vector-Spectromagnetograph (VSM) will demonstrate the need for full Stokes profiles analysis.

2010 Jul 09 10:30 Gregory Rudnick
(University of Kansas)

The Evolution of Red Galaxies in Clusters over Most of Cosmic Time

Tracking the growth of stellar mass in galaxies is a fundamental characterization of the galaxy population. Recent observations have shown that the total mass in L>L* red galaxies has increased by a factor of ~2 at z<1, although at different rates as a function of galaxy mass. Despite the advance made by these studies of the whole galaxy population, until recently it has not been clear if the growth of the red sequence depended on environment. Galaxy clusters are a useful probe of this as they sample the most extreme environments. I will show how the luminosity function (LF) of red-sequence galaxies in clusters and the field has evolved over 50% of cosmic time, highlighting the rapid buildup of the faint cluster galaxy population. I will address how the total mass on the red sequence evolves in clusters and will use this to constrain the mechanisms of how red galaxies can be added to clusters. From this analysis it appears likely that some fraction of the light in recently added cluster red sequence galaxies is currently in the in the form of intracluster stars. Finally, I will show some new results focusing on a newly discovered cluster at z=1.62.

2010 Jul 01 10:30 Paul Crowther
(Univ. Sheffield)

On the upper stellar mass limit

I shall consider current evidence in support of the presently accepted 150 Msun stellar mass limit, and present new studies of the brightest WN-type members within two star clusters, R136 and NGC3603 which challenge this limit. R136 appears to host stars whose masses are significantly in excess of 150 Msun, with consideration given to possibly binarity, on the basis of spectroscopic radial velocity studies, X-ray observations and dynamical effects in dense clusters. The high mass star content of the Arches cluster is placed within this context, as is the potential significance of a higher stellar mass limit for the integrated properties of young, spatially unresolved star clusters and the possibility of pair-instability supernovae in the local universe, as recently proposed for SN2007bi.

2010 Jun 11 10:30 Joe Hennawi
(Max-Planck-Inst. für Astronomie, Heidelberg)

Quasars probing quasars: understanding the physics of massive galaxy formation

One of the most important problems in galaxy formation is understanding the physics which governs the observed bimodality in the galaxy population. Lower mass galaxies are gas rich and form a "blue cloud" in the color magnitude diagram, whereas more massive "red-and-dead" galaxies are gas poor and inhabit the red sequence. As a result, all galaxy formation models include some variant of feedback, which acts to "quench" star formation in massive systems. Observing the formation epoch of red and dead galaxies will shed light on the physics behind this quenching. The strong clustering of luminous quasars at z ~ 2-3 indicates that they are indeed the progenitors of galaxies on the red sequence today. I will introduce a novel technique whereby a foreground quasar can be studied in absorption against a background quasar, resolving scales as small as 30kpc. This experiment reveals a rich absorption spectrum which contains a wealth of information about the physical conditions of ISM and halo gas in massive proto-galaxies. Absorption line modeling techniques will be reviewed, and I'll discuss the implications of these new observations for galaxy formation and feedback scenarios.

2010 May 28 10:30 Jesper Storm


2010 May 07 10:30 Klaus Puschmann
(Inst. Astrofis. Canarias)

A Geometrical Height Scale for Sunspot Penumbrae

The most intriguing problems of solar physics are related to Sunspot penumbrae. A brief introduction will address some of this problems and the models proposed to solve them. The main topic of the talk concerns the construction of a 3D geometrical model of a Sunpot penumbra retrieved from inversions of spectropolarimetric Hinode data and a description of the obtained results shedding new light into some of the open questions. Inversions of spectropolarimetric data deliver the stratification of different physical quantities in an optical depth scale. However, without establishing a geometrical height scale their three-dimensional geometrical structure can not be derived. This is crucial in understanding the correct spatial distribution of physical magnitudes in the penumbral atmosphere and to provide insights into the mechanism capable of explaining the observed penumbral brightness. A genetic algorithm was used to determine the boundary condition (the Wilson depression) for the inference of geometrical heights. The retrieved geometrical height scale permits the evaluation of the correlations of physical quantities inside the resulting 3D geometrical model. The results fit into the uncombed penumbral scenario, i.e., a penumbra composed of flux tubes with channelled mass flow and with a weaker and more horizontal magnetic field as compared with the background field. The ascending material in these elevated flux tubes is hotter and denser than their surroundings. No traces of overturning convection or field free regions are found in the inner penumbral area analysed. The penumbral brightness can be explained by the energy transfer of the ascending mass carried by the Evershed flow, if the physical quantities below z =-75 km are extrapolated from the results of the inversion.

2010 Apr 23 10:30 Roger Haynes
(AIP / innoFSPEC)

InnoFSPEC, astrophotonics and new generation instruments for astronomy

InnoFSPEC Potsdam is now operational. So what is InnoFSPEC about, what exactly is astrophotonics and what is the excitement about? I will outline the goals of InnoFSPEC, unveil the emerging field astrophotonics and hopefully explain why some astronomers are getting excited about it.

2010 Apr 16 10:30 Jens Niemeyer
(Univ. Göttingen)

Simulations of turbulence in the intergalactic medium

TEMP 2010 Apr 09 10:30 Peter Anders Univ. Utrecht GALEV evolutionary synthesis models: a key tool to understand star cluster and galaxy formation Evolutionary synthesis modelling is the key tool to derive physical quantities of unresolved stellar populations, e.g. star clusters and galaxies outside the Local Group. These physical quantities are essential for our understanding how galaxies formed and evolved over a Hubble time. In this context nearby star clusters/globular clusters and high-redshift galaxies provide complementary information. I will give an overview how evolutionary synthesis modelling works, in which respects our GALEV models are more advanced than other models, and identify current limitations of such models. I will conclude with an outlook how I want to tackle the present problems in the framework of joined AIP-AIfA/Bonn Emmy-Noether research group I hope to establish. Feedback and questions after the talk are strongly encouraged.

2010 Mar 26 10:30 Christer Sandin

Unfolding Properties of Mass Loss at the Tip of the Asymptotic Giant Branch

In the final stages of stellar evolution low- to intermediate-mass stars lose their envelope in increasingly massive stellar winds. Matter, which has been processed inside these stars, is thereby returned to the interstellar medium, and mass loss also determines properties of subsequent planetary nebulae. In order to obtain properties of winds at the tip of the asymptotic giant branch we observed weak halos of a set of planetary nebulae in the galactic disk. For this purpose we used the method of integral-field spectroscopy together with a new dedicated data analysis method. In this presentation I will demonstrate the key concepts of our method and also highlight our results. The data shows that mass-loss rates increase strongly in the final mass loss stage, and for several nebulae we derived a densely sampled and steeply increasing temperature gradient into the halo - indicating that the halo is not in thermal equilibrium.

2010 Mar 19 10:30 Marija Vlajic

Outer spiral disks as clues to galaxy formation and evolution

2010 Mar 05 10:30 David Martinez Delgado
(Max-Planck-Institut für Astronomie, Garching)

A survey of stellar tidal streams in nearby spiral galaxies

Within the hierarchical framework for galaxy formation, minor merging and tidal interactions are expected to shape large galaxies to this day. As part of a pilot survey, we have carried out ultra-deep, wide-field imaging of some isolated spiral galaxies in the Local Volume with data taken at small (0.1 to 0.5-meter diameter), robotic telescopes that provide exquisite surface brightness sensitivity.
Our observational effort has led to the discovery of previously undetected giant stellar structures in the halos of these galaxies, likely associated with debris from tidally disrupted satellites. In addition, we confirm several enormous stellar over-densities previously reported in the literature, but never before interpreted as tidal streams.
Our collection of galaxies presents an assortment of tidal phenomena exhibiting strikingly diverse morphological characteristics. In addition to identifying great circles-like features that resemble the Sagittarius stream surrounding the Milky Way, our observations have uncovered enormous structures that extend tens of kiloparsecs into the halos of the central spiral. We have also found remote shells, giant clouds of debris within galactic halos, jet-like features emerging from galactic disks and large-scale, diffuse structures that are almost certainly related to the remnants of ancient, already thoroughly disrupted satellites. Together with these remains of possibly long-defunct companions, our observations also capture surviving satellites caught in the act of tidal disruption. Some of these display long tails extending away from the progenitor satellite as seen in cosmological simulations.
Our comparision with available stellar halo simulations set in a Lambda-Cold Dark Matter cosmology suggests that this extraordinary variety of morphological specimens detected in our survey could represent one of the first comprehensive pieces of evidence to support that the hierarchical formation scenarios predicted by these theoretical models apply generally to galaxies similar to the Milky Way in the Local Volume.

2010 Feb 12 10:30 Cecilia Scannapieco

The formation of disc galaxies in a cosmological context

2010 Feb 05 10:30 Martin Pohl
(DESY/Univ. Potsdam)

Recent advances in high-energy astrophysics

High-energy astrophysics is experiencing a golden age with the recently launched Fermi gamma-ray space telescope and a number of atmospheric Cherenkov telescope in operation. Recent observational results on shell-type supernova remnants based on gamma-ray data as well as high-angular-resolution data of nonthermal X-ray emission indicate an amplification of magnetic fields in addition to the efficient acceleration of charged particles. I shall review kinetic simulations that can shed light on the microphysics behind both particle acceleration and magnetic-field amplification.

2010 Jan 29 10:30 (sharp) Rainer Arlt
(Astrophys. Inst. Potsdam)

The stellar perspectives of MHD instabilities (application talk)

Instabilities are creating structures in many astrophysical objects. The general properties of MHD instabilities will be discussed and their domains of applications explored. The focus will be on stars. Global unstable modes are the ones which leave the most obvious traces on the surfaces of the Sun and stars, and the implications for stellar activity cycles are discussed. MHD instabilities impose upper limits for magnetic fields in all types of stars and deliver constraints for the topology of the fields. The presentation is thus also a path from general to observable MHD.

2010 Jan 22 10:30 Georg Lamer


2010 Jan 21 10:30 (sharp) Alfio Bonanno
(Osservatorio Astrofisico Catania, INAF)

MHD instabilites in Astrophysics: recent results and future perspectives (application talk)

The past decade has seen an enormous upsurge in the area of theoretical and experimental magneto-fluid dynamics, mostly due to the possibility of performing large scale numerical simulations and laboratory experiments. In this talk recent results on the problem of the stability of axisymmetric field configurations with a non-trivial topological structure will be reviewed and their consequences in the context of Ap stars, Neutron stars and astrophysical jets will be discussed. Moreover, the opportunity offered by combining ground-based projects (PEPSI@LBT, STELLA ) and space projects (the Kepler satellite) to sound stellar cycles and dynamo theory of solar-type stars will be explored.

2010 Jan 15 10:30 (sharp) Eun-jin Kim
(Dept. Applied Mathematics, Univ. Sheffield)

Magnetohydrodynamic turbulence and beyond, in astrophysical and laboratory plasmas (application talk)

I will discuss various aspects of magnetohydrodynamic turbulence, how it can interact with large-scale features such as shear flows (differential rotations) and magnetic fields to produce intermittency, self-organisation, and other important phenomena. In particular, I will consider how turbulence affects transport of angular momentum, magnetic fields (e.g. dynamos), chemical species, heat, etc., and demonstrate the importance of a proper understanding of multi-scale interactions. Special emphasis will be placed on comparing astrophysical and laboratory (fusion) applications, and what each can learn from the other.

2009 Dec 10 16:00 Leonid Kitchatinov
(Inst. Solar-Terrestrial Phys., Irkutsk)

On stellar differential rotation theory (application talk)

2009 Dec 10 10:00 ISC

Workshop "Observing facilities" 10:00-16:00

2009 Dec 04 10:30 Bruno Leibundgut
(ESO, Garching)

Supernova Cosmology 2010

The first decade of Dark Energy has passed and the accelerating expansion of the universe seems to stay with us for a while. Supernovae remain at the moment the prime indicator for individual cosmological distances and the past decade has seen several major supernova surveys. I will summarize the current status of the supernova results with a critical assessment of the limitations and challenges for luminosity distances as measured by supernovae.

2009 Nov 27 10:30 Volker Springel
(Max Planck Inst. for Astrophysics, Garching)


2009 Nov 13 10:30 Wolfgang Schmidt
(Kiepenheuer Institute, Freiburg)

The SUNRISE mission: observing the Sun like never before

SUNRISE is an international project aimed at high-resolution observations of the Sun using a 1 meter aperture solar telescope on a NASA long-duration balloon flight. The talk gives an overview of the SUNRISE observatory, and its first science flight from Kiruna, Sweden to Somerset Island, Canada. The data include UV images never seen before, and high-quality magnetic field measurements. Some preliminary data are presented which give promise of gaining new insight into solar surface magnetism. TEMP 2009 Nov 06 10:30 Udo Ziegler AIP NIRVANA

2009 Nov 06 10:30 Mark Westmoquette
(University College London)

Spatially-resolved studies of super star cluster feedback in starburst galaxies

Understanding starburst-driven outflows is important for many reasons within the context of galaxy evolution. However, to understand outflows on the large scale, the details of feedback mechanisms from individual star clusters must first be understood. I will discuss recent results from a number of high spatial and spectral resolution integral field spectroscopic studies of the ionized gas environment within a sample of nearby starbursts. These studies are allowing us to build up a picture of (1) how power is fed from super star clusters into the surrounding ISM, (2) how the ISM properties affect how this power is directed, and (3) how the gas outflows evolve structurally and energetically towards the larger-scales.

2009 Nov 04 10:30 Matthias Rempel
(HAO, Boulder)

Radiative MHD simulations of sunspot structure
(Wempe lecture)

2009 Nov 02 11:00 Juri Poutanen
(Univ. of Oulu)

Accretion-powered millisecond pulsars

The launch of Rossi X-ray Timing Explorer in 1995 opened a new era instudies of neutron stars. The high sensitivity and time resolution of the PCA instrument allowed us to study with unprecedented precision the variability of black holes and neutron stars. About 20 neutron stars showing highly coherent oscillations at hundreds of Hz during thermonuclear explosions at their surfaces have been discovered. Twelve "accreting millisecond pulsars" demonstrating coherent pulsations in their persistent emission, with the record-holder rotating 599 times a second, are now known. These sources provide a proof of the origin of radio millisecond pulsars as a result of the neutron star spin-up at the accretion phase in low-mass X-ray binaries.
I will review the data on accreting millisecond pulsars. I will describe how the studies of the pulse profiles and their evolution with accretion rate can be used to put constraints on the equation of state of matter at supra-nuclear densities and the geometry of the system. The use of the pulsars to study the neutron star spin-up and spin-down as well as the orbital evolution of the binary will be discussed.

2009 Oct 23 10:30 Thomas Naumann
(DESY, Zeuthen, and ATLAS experiment, CERN)

Big Bang in the Lab - Physics at the LHC

First we discuss the fundamental questions of physics to be solved at the Large Hadron Collider LHC of CERN. Then the accelerator, the experiments and their measurement strategies are described. Finally, the status of the largest research project of mankind is given.

2009 Oct 16 10:30 Anders Johansen
(Leiden Obs.)

Computer simulations of accretion discs: planet formation and large scale magnetic fields

I present two recent results on the dynamics of magnetised accretion discs. The magnetorotational instability thrives off the Keplerian differential rotation and makes the gas turbulent, transporting mass and angular momentum by Reynolds and Maxwell stresses. In very large simulation domains time fluctuations in the Maxwell stress lead to a large scale variation in the orbital speed of the gas. The analysis of such zonal flows gives an interesting perspective into the nature of accretion disc dynamo processes. Zonal flows also concentrate solid particles, which gives a path to forming km-sized planetesimals from rocks and boulders. Discs penetrated by strong azimuthal fields are also unstable to the Parker instability. The buoyant magnetic fields rise to form big arcs, and the vertical field component of the arcs is in turn unstable to the magnetorotational instability. A turbulent state with efficient angular momentum transport follows. We observe that the azimuthal magnetic field does not escape from the disc, but is replenished as the gas parcels stream down towards the mid-plane along inclined field lines.

2009 Oct 15 10:00 Martin M. Roth

Astrophysical instrumentation an astrophotonics - innovations in observational astronomy
(application lecture for W2 professorship)

Over the past three decades, Astronomy has experienced a period of enormous progress and growth - a period which is sometimes alluded to as the "Golden Age of Astrophysics". Next to progress in the- ory and numerical simulations, novel detectors and instrumentation have played an important role in this development. With an emphasis on multi-channel spectroscopy techniques, I shall review major innovations in ground-based optical and near infrared astronomy, and highlight their impact on our present understanding of the structure and evolution of the universe.
While instrumentation developments in the 20th century were largely influenced by electronics and computers, I shall argue that it is becoming more and more apparent how photonics technologies are going to dominate innovations in the 21st century, with a potential which is as yet largely unexplored. I shall present examples for promising ongoing astrophotonics developments, and outline a vision for future directions in instrumentation research.

2009 Oct 09 10:30 Heike Rauer
(DLR Berlin)

The CoRoT Mission

The CoRoT satellite was launched on December 2006 with two goals: to search for extrasolar planets and study the interior structure of stars. So far, six planets and a brown dwarf (with 20 Jupiter masses) have been reported and several results on stellar seismology are published. Among the highlights of planet discoveries from CoRoT is a small terrestrial planet, CoRoT-7b, with less than two Earth radii size. The present status of the CoRoT mission, with emphasis on the steadily growing CoRoT planet family, will be reported. Finally, an outlook to proposed future transit detection missions (PLATO) and prospects for characterization of transiting terrestrial planets will be given.

2009 Sep 11 10:30 Institute Conference

All-institute meeting

TEMP 2009 Sep 18 10:30 Claudio Llinares AIP tba.

2009 Sep 04 10:30 Wolfgang Gieren
(Universidad de Concepcion)

The Araucaria Project: improved distances to nearby galaxies from Cepheids, eclipsing binaries and blue supergiants

The general goal of the Araucaria Project is to provide an improved calibration of the first rungs of the cosmic distance ladder, by improving some of the most important stellar techniques of distance measurement and applying them on a sample of nearby galaxies. In my talk, I will report on recent results obtained from Cepheid variables and blue supergiant stars. I will also give an update on our program to measure the LMC distance, and its depth structure in the line of sight with unprecedented accuracy from late-type eclipsing binary systems we have discovered in the OGLE 2 and OGLE 3 surveys.

2009 Jul 10 10:30 Christian Wagner

Probes of Dark Energy using Cosmological Simulations

More than a decade after the first observations of distant Type Ia Supernovae (SN Ia) the cause of the observed acceleration of the universe remains an open question. The nature of the dark energy believed to be driving the current accelerated expansion of the universe is one of the greatest puzzles in the physical sciences, with deep implications for our understanding of the universe and fundamental physics. Over the past few years, the observational evidence for the existence of dark energy has grown, yet in order to improve our understanding of dark energy its properties need to be probed. So far four main observational probes have been explored: SN Ia, baryon acoustic oscillations, clusters of galaxies, and weak lensing. Of these probes the last three depend on the large-scale structure of the universe which formed by nonlinear gravitational clustering. Using cosmological N-Body codes we can simulate the gravitational evolution of the matter density field. This enables us to investigate the nonlinear effects and make theoretical predictions regarding these probes. In this talk I will first review the basic principles of the probes themselves and then present our main results.

2009 Jul 03 10:30 Andreas Quirrenbach
(Zentr. f. Astrophys./Landessternw.)

Interferometry with Starlight

Interferometry at visible and near-IR wavelengths has become an important tool of stellar astrophysics. Interferometric techniques have developed rapidly over the past couple of decades; a number of facilities are currently producing scientific results on topics as diverse as fundamental stellar parameters, circumstellar matter, and active galactic nuclei. In the near future, the PRIMA facility will provide enhanced capabilities at ESO's Very Large Telescope Interferometer, including narrow-angle astrometry. A large number of additional questions can be addressed with interferometers in space, and with a large next-generation interferometer on the ground. The talk will provide an introduction into interferometric techniques, and provide an overview of the most exciting applications of interferometry to astrophysics.

2009 Jun 26 10:30 Martin Asplund

Does the Sun have a subsolar metallicity?

The solar chemical composition is an important ingredient in our understanding of the formation, structure and evolution of both the Sun and our solar system. Furthermore, it is an essential reference standard against which the elemental contents of other astronomical objects are compared. In recent years the solar abundances of the most common metals -- C, N, O and Ne -- have undergone a quite dramatic downward revision, driven by our work on developing realistic 3D hydrodynamical solar model atmospheres, non-LTE line formation and improved atomic/molecular data. While welcomed by most areas of astronomy, these changes have caused a great deal of consternation for helioseismology. I will present our recently completed work on redetermining the solar abundances of all elements, which will appear in ARAA later this year. I will also discuss how the Sun compares with other solar-type stars. Surprisingly the Sun is unusual in its chemical properties, a fact that most likely is due to it hosting planets. Our findings open the enthralling prospect of being able to identify stars harbouring planets purely from their chemical compositions.

2009 Jun 19 10:30 Jürgen Stutzki
(Univ. Köln)

Herschel: a new view into the cold universe

ESA has successfully launched its Herschel Space Observatory on May 14th, 2009. Herschel is aimed at studying star formation and galaxy evolution. With its unique suite of three focal plane instruments, covering the full parameter space in relevant wavelengths and spectral resolution, Herschel will open a new window for the observation of the cold universe. The talk will give an overview of the Herschel Space Observatory and its three instruments, and will outline the new opportunities given by Herschel, also in context of the other major submm- and FIR observatories. Some special emphasis will be put on the science drivers and perspectives for high resolution spectroscopy of the interstellar medium with the HIFI-instrument. TEMP 2009 Nov 20 10:30 Natasha Maddox AIP tba.

2009 Jun 12 10:30 Sylvain Veilleux
(Univ. Maryland, MPE Garching)

Galaxy mergers, ultraluminous infrared galaxies, and quasar activity

Galaxy merging is a key driving force of galaxy evolution. In hierarchical CDM models of galaxy formation and evolution, merging leads to the formation of some elliptical galaxies, triggers major starbursts, and may account for the growth of supermassive black holes and the formation of quasars. In order to assess quantitatively the physics of the merger process and its link to elliptical galaxy formation and QSO activity, we must first understand the details of galaxy merging and its relationship to starbursts and AGNs in the local universe. Here I present the recent results from a comprehensive multiwavelength investigation of the most luminous mergers in the local universe, the ultraluminous infrared galaxies (ULIRGs) and the quasars. The issues of the occurrence, importance, and dusty cycle of black hole driven nuclear activity in these objects will be covered along with their host galaxy properties and the evidence for massive gas flows in and out (past and present) of their central cores. The implications of these results on our understanding of ULIRGs and quasars in a cosmological context will also be addressed.

2009 May 29 10:30 Jaime Hoyos

Magnetic field decay processes in neutron stars

2009 May 27 09:30 13. Leibniz-Kolleg
(all-day colloquium at AIP, 09:30 to about 17:00)

Astrophysics and the search for extraterrestrial life


2009 May 25 14:00 Special Colloquium

Wempe Award Ceremony for Dr. Matthias Rempel

2009 May 08 10:30 Igor di Varano

ICE-T: two eyes pointing at Dome C

2009 Apr 24 10:30 Stefan Gottlöber

Constrained simulations of the local universe

During the last decade our understanding of the evolution of structure in the universe grew substantially. Due to the non-linear nature of the gravitational dynamics and the complicated gas-astrophysical processes numerical simulations on modern supercomputers have been the driving force behind much of this theoretical progress.
Cosmological simulations must cover a large dynamical and mass range. A representative volume of the universe should be large, but this comes at the expense of the resolution. To overcome this problem a new, and almost orthogonal but yet complementary, approach to cosmological simulations has been introduced over the last few years. This consists of using observations of the nearby universe as constraints imposed on the initial conditions of the simulations. The resulting constrained simulations successfully reproduce the local large scale structure, where 'local' means a few tens of megaparsec around the Milky Way. These simulations are the numerical analog of the 'Near Field Cosmology', and provide a laboratory for studying the formation of our Local Group and its environment. I will review our constrained simulations performed in collaboration of research teams in Spain, Israel, Germany and USA.

2009 Apr 17 10:30 Oliver Schnurr
(Univ. of Sheffield, UK)

The most massive stars

Which are the most massive stars and how massive are they? Fundamental questions of stellar astrophysics suffer from an almost complete lack of truly empirical evidence when it comes to stars with the highest masses both on and evolved off the main sequence. Recent theoretical and observational work suggests that the most massive stars known are to be found not among bright O stars, but among a luminous, hydrogen-rich subgroup of Wolf-Rayet stars, the so-called WN5-7ha stars, which, despite their being near the upper main-sequence, are able to drive strong winds due to their extreme luminosities. Directly weighing such objects by Keplerian orbits in binaries is the only way to obtain reliable masses for these stars. I will present results that have been obtained from the study of spectroscopic binaries, and present the most massive stars known so far.

2009 Mar 27 10:30 Peter Kalberla
(Argelander Inst. Bonn)

The HI distribution in the Milky Way.

The aim of this talk is to review the global structure of the Milky Way HI disk. The investigations are based on a self-consistent determination of the Galactic mass distribution from the flaring of the HI gas layer (the balance of turbulent gas pressure against k_z). 90% of the HI gas is confined within a thin disk with a two-phase structure (cold and warm neutral medium). This disk is warped and the HI scale height is strongly flaring. The radial distributions of surface and mid-plane densities decrease exponentially. The gaseous disk has an extension of 35 kpc, a scale length that may be explainable by the Milky Way mass distribution. 10% of the HI gas is "anomalous", located above the plane and best described by a thick disk with a scale height exceeding the thin disk by a factor of ten. Most of this gas is in clumps with a core-envelope structure in pressure equilibrium with a confining hot ionized medium. The halo gas is lagging behind the rotating disk.

2009 Mar 20 10:30 Chandra Wickramasinghe
(Cardiff Univ./Cardiff Centre of Astrobiology)

Astrobiology: past reflections and futures hopes

The history of astrobiology will be traced from its ancient roots to modern developments. I shall recount my own involvement in this field which started in a most unlikely way with in­vestigations into the composition of interstellar dust. In the 196's there was little doubt in the minds of astronomers that the dust was inorganic. My collaborations with Fred Hoyle led eventually to a conclusion, now accepted without dissent, that interstellar dust has an organic composition that is undoubtedly relevant to biology. I shall summarise the current arguments for and against panspermia, and speculate what the future might hold for astrobiology.

2009 Mar 13 10:30 Noam Libeskind

The satellites of the Milky Way

2009 Feb 27 10:30 Jose Manuel Ramirez Velasquez


2009 Jan 30 10:30 Fernando Atrio-Barandela
(Univ. de Salamanca)

Large scale peculiar velocities of clusters of galaxies

Peculiar velocities of galaxies, derived using distance estimators, are plagued with systematic effects and are unreliable beyond 100 Mpc/h. In Kashlinsky & Atrio-Barandela (2000) we proposed to measure peculiar velocities of clusters of galaxies using the temperature anisotropies on the Cosmic Microwave Background generated by the hot X-ray emitting gas. Using this technique we have recently found a bulk flow velocity of amplitude 600-1000 km/s in the same direction as the CMB dipole and encompasing a sphere of 300 Mpc/h radius. We shall discuss the cosmological implications of this measurement.

2009 Jan 16 10:30 Kristin Riebe

Subhaloes and Their Tidal Debris in Cosmological Simulations

Galaxies like the Milky Way usually are not alone, but are surrounded by a number of smaller companions, the satellite or dwarf galaxies. While they orbit around their host galaxy, tidal forces strip matter from the satellite galaxies, which typically leads to the formation of tidal streams and can result in the final disruption of the smaller galaxy. Such tidal streams as witnesses of the merging history of galaxies have already been found in a number of galaxies, especially in the environment of our own Milky Way and around the Andromeda galaxy. Their properties are expected to correlate with the satellite's progenitor as well as with the dark matter halo of the host galaxy, in which the system is embedded. Even if the satellite is already disrupted, one may recover estimates of its original mass and orbit by investigating the remaining tidal debris material.
Numerical simulations of isolated satellite galaxies in static host potentials have already revealed several correlations, but so far none has considered the formation of tidal streams in their full cosmological context, using cosmological simulations. In such simulations, which model the evolution of the Universe shortly after its beginning until today, dark matter host halos with a wealth of subhalos are forming naturally. If these halos and subhalos contain enough baryonic matter, they can be considered as the dark matter counterparts to the observed galaxies and satellite galaxies. Studying subhalos therefore lays the ground for understanding the satellite galaxies as well.
In this talk, I will present some highlights of our studies on subhalos and their tidal debris in cosmological simulations, mainly concentrating on the question what tidal streams actually can tell us about the progenitor satellite and the underlying host halo.

2008 Dec 16 10:30 Kenneth Freeman
(Mt. Stromlo Obs., Australia)

Wempe Award Colloquium: Galactic Disks

I will discuss some of the issues about galactic disks which are still not well understood. These issues include the structure and chemical evolution of disks, disk heating, stellar moving groups, thick disks, and LambdaCDM problems on galactic scales.

2008 Dec 15 14:00 Special Colloquium

Wempe Award Ceremony

Opening, laudatio, and ceremony
Gerry Gilmore (Cambridge, UK): Milky Way formation - what needs to be explained?

2008 Dec 12 10:30 Frank Spahn
(Univ. Potsdam)

Planetary Rings - natural dynamical labs for disks in space

2008 Dec 05 10:30 Carsten Denker

Chromospheric Fine-Structure -- GREGOR Science Drivers

Generation and dissipation of small-scale solar magnetic features are responsible for the dynamics above the photosphere. Observations of small-scale magnetic fields, with the highest resolution possible, are crucial to our understanding of mass and energy transport throughout photosphere, chromosphere, transition region, and corona. In August 2008, we obtained quiet Sun observations with the Göttingen Fabry-Perot Interferometer (GFPI) at the Vaccum Tower Telescope (VTT), Tenerife. We present some preliminary data obtained in the chromospheric Halpha and photospheric FeI 630.2 nm lines. We focus on mini-filaments, which are a small-scale phenomenon of the solar chromosphere. They frequently occur across the entire disk. They share a variety of characteristics with their larger-scale cousins and may serve as a proxy for more complex systems. In the case of small-scale eruptive filaments, only single, small-scale loop systems are involved. Furthermore, they are supported by simple magnetic field configurations, either magnetic bipoles or well-defined multipoles, easing their theoretical description. Mini-filaments might therefore be a stepping stone for our understanding of solar eruptive events such as filament/ prominence eruptions and coronal mass ejections (CMEs).
Furthermore, to illustrate the science capabilities of imaging spectropolarimetry, we will present the current GFPI implementation at the VTT, plans for its migration to GREGOR, and an update of the GREGOR status

2008 Nov 28 10:30 Anatoly Piskunov
(Inst. Astronomy, RAS, Moscow)

Open clusters as the framework of the galactic disk population

I summarize the results of the study of Galactic open clusters carried out in tight collaboration with Kiev, Potsdam and Heidelberg teams. The project is based on the all-sky catalogue ASCC-2.5 (a collection of uniform kinematic, photometric and spectral type data) designed for Galactic studies. In these data we were able to identify 520 previously known open clusters and to discover 130 new/unknown objects. All identified clusters were passed through a thorough clearing from contaminating fore/background stars, which resulted in a unique membership list based on photometric, kinematic and spatial constraints. The basic features of this membership are the uniformity of the approach and data all over the sky, and the absence of limitations by a detector FOV size, typical of many other star cluster studies. As the analysis has shown, the sample is complete (i.e. we know practically all clusters) to about 850 pc from the Sun. This enabled us to carry out a comprehensive study of the local cluster population in relation with different issues of star formation and evolution in the Galactic disk. Some of the results can be regarded as hints on the evolution of the extragalactic stellar populations.

2008 Nov 21 10:30 Franziska Piontek

Simulations of disk galaxy formation: a systematic study

The formation of disk galaxies is one of the big open questions in galaxy formation theory. Simulated disks are plagued by various problems, most notably a strong loss of angular momentum leading to an object with a compact bulge, and a failure to fit the observed scaling relations for spiral galaxies. In the last few years, there have been several encouraging improvements resulting in more realistic disks. This has been achieved, among others, by increasing the resolution of the simulations and by various improvements of the recipes for star formation and feedback. However, it remains unclear, which (or which combination) of these effects actually is responsible for the more realistic disks. We therefore are conducting a systematic study of resolution and feedback recipes using the N-body code Gadget2 (Springel 2005), and I will present first results of this study.

2008 Nov 14 10:30 Eric Fossat
(Univ. Nice Sophia-Antipolis)

Surface turbulent layer and peculiar properties of astronomical seeing at Concordia, Antarctica

Since the opening of Concordia for the winter, in 2005, almost 4 years of continuous site testing have provided lots of data. The atmospheric properties of the site are now well known, at least regarding some parameters, specially the very peculiar properties of the turbulence. The surface seeing is quite poor, but 95 percent of the turbulent energy is in the first 30 meters or so. The statistical properties of these 30 meters as well as the outstanding seeing above this thin turbulent layer are statistically well bracketed now. Many other parameters of the turbulence will also be presented. The clear sky statistics and the photometric quality remain less extensively explored, but the first photometers that have started to be operated in 2007 begin to provide some useful indications.

2008 Nov 07 10:30 Andrea Merloni
(Munich Excellence Cluster Universe / MPE)

A synthetic view of AGN evolution and supermassive black holes growth

In the last decade, a combination of high sensitivity and spatial resolution observations in the extragalactic domain, and of coordinated multi-wavelength campaigns on galactic objects have revolutionized our understanding of black holes astrophysics on all mass scales. This has led to substantial progress towards super-unification schemes for Active Galactic Nuclei, in which the large variety of different AGN classes can be classified based on fundamental physical parameters only, such as mass, accretion rate and kinetic energy output. I will describe the constraints available from a study of AGN evolution synthesis models on the growth of the SMBH population in the two main modes observed ('kinetic-' and 'radiatively-dominated', respectively). SMBH always show a very broad accretion rate distribution, and I'll discuss the consequences of this fact for our understanding of observed AGN fractions in galaxies. I'll then show how SMBH mass function evolves anti-hierarchically, i.e. the most massive holes grew earlier and faster than less massive ones, and I will also derive tight constraints on the average radiative efficiency of AGN. Finally, constraints on the redshift evolution of the AGN kinetic luminosity function will be briefly discussed and compared with the radiative output of the evolving SMBH population, thus providing a robust physical framework for phenommenological models of AGN feedback within structure formation.

2008 Oct 24 10:30 Steffen Knollmann

Structure of Dark Matter Haloes in Scale-Free Cosmologies

2008 Oct 17 10:30 Leonid Kitchatinov

Stellar differential rotation: origin and models

2008 Sep 15 16:00 Naoki Itoh
(Sophia Univ., Tokyo)

The Sunyaev-Zeldovich Effect: Seeing Galaxy Clusters through the Cosmic Microwave Background

Sunyaev and Zeldovich predicted in 1972 that microwave background photons coming from the directions of galaxy clusters will show spectral distortion due to the Compton scattering by high-temperature electrons that exist in the galaxy cluster plasma. This phenomenon was observed by Gull and Northover in 1976. Recent Sunyaev-Zeldovich effect observations with the use of interferometric telescope arrays by University of Chicago group led by John Carlstrom have revolutionized the field. By this method detailed Sunyaev-Zeldovich effect maps of about 60 galaxy clusters have been obtained by the University of Chicago group. Many forthcoming Sunyaev-Zeldovich survey observation projects of galaxy clusters will reveal thousands of galaxy clusters and will shed light on the evolution of the universe, providing us with a method to measure the Hubble constant, the dark matter content in our universe, and the dark energy content in our universe. On the theoretical side, accurate relativistic corrections to the Sunyaev-Zeldovich effect have been calculated by our group as well as some other groups, thus enabling a precision theoretical treatment. These relativistic corrections are essential for the forthcoming high-frequency observations of galaxy clusters.

2008 Sep 10 14:00 Daniel Zucker
(Institute of Astronomy, Cambridge, UK)

Galaxy Assembly on our Doorstep

In hierarchical scenarios, large galaxies like the Milky Way and M31 form via the merger and accretion of smaller systems, and evidence of these processes can be found in the stellar streams and the surviving satellites surrounding each galaxy. The advent of large-area astronomical surveys like the Sloan Digital Sky Survey (SDSS) has revolutionised our ability to find and study Local Group stellar structures at unprecedentedly faint surface brightnesses, and these capabilities are expanding, with numerous projects now underway or starting in the next few years - e.g., RAVE, SDSS-III/SEGUE, PanSTARRS and Skymapper, and the Gaia mission. I will give an overview of the flood of recent stream and satellite discoveries in the Local Group made with data from SDSS and other surveys, and present the results of detailed follow-up observations with both ground- and space-based telescopes. These new discoveries are already providing important constraints for models of galaxy formation, as well as yielding clues to the behaviour of dark matter on the smallest scales. In coming years, the symbiotic evolution of observational resources and theoretical models will lead to a new understanding of the processes involved in galaxy formation in the Local Group - and by inference, the Universe.

2008 Sep 01 14:00 Special Colloquium

10000 MHD-Tage in Potsdam

Klaus Strassmeier - Bereichsdirektor des AIP für Kosmische Magnetfelder
Beiträge von Frank Stefani, Marcus Gellert, Horst Balthasar, Nobert Seehafer, Manfred Schüssler
Pause, anschließend
Beiträge von Manfred Küker, Hans-Erich Fröhlich, Detlef Elstner, Oliver Gressel
Günther Rüdiger: 10000 Tage MHD in Potsdam
ca. 17:15: BBQ

2008 Aug 29 10:30 Jorge Penarrubia
(Univ. of Victoria)

The Local Group: A challenge for Cosmological models

The Local Group (LG), formed by a sizable catalogue of galaxy members that spans almost seven decades in luminosity, from 10 to 10 Lsol, and that locate at distances that permit to resolve individual stars, represents a challenge for our cosmological paradigm of galaxy formation. In the last few years, the amount of information on LG members has experienced a step-function increase due to the availability of wide-field cameras and multi-fiber spectrographs. And the future prospects are also bright: currently undergoing surveys will go to deeper luminosities, increase the sky coverage and likely discover dozens of new LG galaxies. Also, in ~2013, five years from now, GAIA will start to chart a three-dimensional map of our Galaxy, revealing its structure with unprecedented detail. Presently, it is unclear whether we have the necessary theoretical tools to construct models that can be contrasted against the incoming data at a similar level of detail. Predictions from cosmological N-body simulations are severely hindered by our lack of understanding of star formation/feedback processes and by the high computational resources required to simulate gas dynamics. This situation will not likely improve before we start to receive data from GAIA.
In this talk I will discuss a research strategy that combines the work of observers and theorists to build up a new generation of cosmological models specially designed to exploit the data gathered by ground-base surveys (SDSS, SEGUE, RAVE, Pan-STARRS) and spatial missions like GAIA.

2008 Jul 18 10:30 Matthias Schreiber
(Univ. Valparaiso, Chile)

The SDSS PCEB-project: understanding close binary evolution from SDSS/SEGUE binaries.

Close binaries containing a compact object make up a wide variety of objects such as white dwarf binaries, some of which are SN Ia progenitors, or close neutron star binaries, which are possible progenitors of short Gamma-Ray bursts. The evolution of all close binaries depends crucially on the rate at which angular momentum is extracted from the binary orbit. The two most important sources of angular momentum loss are the common envelope phase and magnetic braking. Both processes are known for long but still poorly understood, and significant progress will probably only be achieved if they can be calibrated using innovative observational input. By identifying the post common envelope binaries among SDSS white dwarf/main sequence binaries and measuring their binary parameters, we provide new constraints for further development of binary evolution theory. So far we identified 85 new post common envelope binaries (PCEBs) and measured 38 orbital periods. I will discuss the properties of our SDSS-PCEB sample in the light of current theories of compact binary evolution. The main results so far are: (i) The fraction of PCEBs among SDSS white dwarf/main sequence binaries is about ~40% and sensitively depends on the mass of the secondary star as predicted by the disrupted magnteic braking hypothesis. (ii) The orbital period distribution of SDSS PCEBs is dominated by short orbital period systems indicating a low efficiency of the common envelope phase.

2008 Jul 04 10:30 Emre Isik
(Max Planck Inst. Solar System Research)

Generation, storage, and transport of magnetic flux in cool stars

Observational and theoretical studies of solar magnetic activity indicate that the large-scale azimuthal magnetic field on the Sun is generated and stored near the bottom of the convection zone. In the course of magnetic field amplification, the toroidal magnetic field becomes unstable to perturbations (e.g., by convective flows). The instabilities lead to rising loops that reach the surface in the form of bipolar magnetic regions (BMRs). The emergence and surface transport of tilted BMRs contributes the regeneration of the poloidal field. We have developed a model, which considers processes of (i) the generation of toroidal magnetic flux, (ii) the instability and rise of magnetic flux through the convection zone, and (iii) the redistribution of magnetic flux on the surface. Following a brief discussion of the storage of magnetic flux in the dynamo layer, the results of the combined model will be presented, with applications for the Sun and rapidly rotating cool stars. The patterns and time evolution of magnetic regions on active stars will be discussed, in the view of the numerical simulations and observations.

2008 Jun 24 10:30 Bruce Elmegreen
(IBM Watson Research Center)

Star formation in high redshift galaxies

The Hubble Space Telescope for optical and near-infrared light and the Spitzer Space Telescope for the infrared have opened up a view of star formation in young galaxies that has never been possible before. Because the most distant galaxies are viewed as they were when light left them long ago, we can see the various steps of galaxy formation throughout time. Our work in the last three years has concentrated on the nature of star formation in these galaxies, many of which are peculiar by the standards of our own neighborhood. The dominant peculiarity is the presence of enormous young clusters and star complexes in the disk systems. These complexes are 1000 times more massive than any star forming regions in galaxies today, and yet they appear to form by standard processes, which begin with a localized collapse of disk gas. The galaxy disks are also smaller and thicker than today's spiral galaxies, and many have less than 1/10 the mass of the Milky Way. This combination of small galaxies and big star complexes makes the youngest disks look very patchy, yet, remarkably, the average positions of these patches, if they were to be smoothed out in each disk, has the same radial density profile as that observed in the more normal spiral galaxies that are also in deep fields. The thicknesses of the star complexes are also about equal to the galaxy thicknesses. Thus it appears that spiral galaxy disks form by the dispersal and dissolution of giant star complexes, which form by gravitational instabilities in thick and turbulent gas layers. Numerical simulations suggest that this process is accompanied by the formation of the bulge and perhaps even black holes in the bulge, through the coalescence of the clumps and their individual black holes that migrate to the center.This process seems to accompany the growth of galaxy disks over cosmic time, indicating that the growth occurs primarily by the accretion of gas for systems that end up as spirals. Clumpy disk star formation also precedes the formation of spirals and ellipticals, going back to the bandshifting limit of the ACS camera on HST, which is z~5. Thus most star formation in the Universe begins in disk systems, and from these, all of today's Hubble types eventually form.

2008 Jun 13 10:30 Nazaret Bello González
(Inst. für Astrophysik, Göttingen)

2D solar spectropolarimetry of high spatial and spectral resolution

For the detection and the study of small-scaled magnetic fields on the Sun, it is important to obtain observations with both high spatial resolution and high polarimetric sensitivity. The upgrades of the Göttingen FPI (spectral resolution of 25mÅ, at 617nm) + full Stokes polarimeter + Adaptive Optics (KAOS) + speckle reconstruction techniques, provide broadband images of 0.25" spatial resolution and magnetograms of 0.33", with minimised seeing induced signals yielding a polarimetric sensitivity of ~0.002 Ic. A description of the optical system as well as results from the analysis of intensity maps, Dopplergrams and magnetograms from quiet and active regions on the Sun will be presented.

2008 Jun 06 10:30 David Wiltshire
(University of Canterbury, New Zealand)

Dark energy without dark energy

I present an unexpected explanation for dark energy, purely within general relativity with matter obeying the strong energy condition. Cosmic acceleration is explained quantitatively, as an apparent effect due to quasilocal gravitational energy differences - and hence clock rate variance - that arise in the decoupling of bound systems from the global expansion of the universe. Although the universe was initially very smooth, today it is very inhomogeneous on scales less than 200 Mpc, with clusters of galaxies strung in filaments and bubbles surrounding huge voids. Accounting for spatial curvature and gravitational energy gradients between galaxies and the volume average location in voids, leads to a recalibration of average cosmological parameters.
I present a model of the universe based on this proposal, which passes three key independent cosmological tests: supernova luminosity distances, the angular scale of the sound horizon in the cosmic microwave background (CMB) and the baryon acoustic oscillation scale in galaxy clustering statistics. It may simultaneously resolve particular anomalies, including primordial lithium abundances and CMB ellipticity. The expansion age is increased allowing more time for structure formation. Best-fit parameters and implications will be discussed. Unique predictions include a quantifiable variance in the Hubble flow below the scale of apparent homogeneity, consistent with the observed "Hubble bubble" feature, which sheds new light on the decades long debate about the value of the Hubble constant.

2008 May 22 11:00 Manfred Cuntz
(Univ. of Texas, Arlington)

Astrophysics and Astrobiology Research at UT Arlington

In my talk, I will provide an overview of ongoing research projects in astrophysics and astrobiology at the University of Texas at Arlington. Our research focus encompasses various fields and topics, including solar physics, star-planet interaction, orbital stability of planets in stellar habitable zones, and the effects of UV radiation on biomolecules in circumstellar environments. Two of our most recent results include the derivation of stringent criteria for the orbital stability of planets in stellar binary systems and, in collaboration with members of Harvard CfA, the study of planet-induced X-ray emission in HD 179949 (F8 V).

2008 May 16 10:30 David Martinez Delgado
(IAC, Tenerife)

Tidal streams in the Milky Way and external galaxies

2008 May 09 10:30 Jaime Forero


2008 Apr 25 10:30 Isabelle Gavignaud

Powering the faint end of AGN luminosity function

The tight correlation between masses of supermassive blach holes (SMBH) and their hosting galactic buges, suggest a link between galaxy formation and SMBH accretion history. Therefore, studying AGN demographics provides a tool to trace the growth of SMBH up to high redshift, and is a first step towards understanding connections with galaxy formation.
In this colloquium I will present the work we have been doing to determine the masses and accretion rates of the SMBH population at the faint end of the AGN luminosity function. For this purpose, we used one of the deepest spectroscopic samples of AGN currently available, extracted from the VIMOS VLT Deep Survey (VVDS), and found that, in contrast to what is found for AGN of higher luminosities, there is a substantial fraction of black holes with low accretion rates (far below their Eddington limit). We speculate that these may be AGN on the decaying branch of their light-curves, well past their peak activity. This would agree with recent theoretical predictions of AGN evolution.

2008 Apr 18 10:30 Rainer Spurzem
(Univ. Heidelberg)

Black Holes, Gravitational Waves, grids for GRAPEs and other computer games...

During cosmological structure formation galaxies merge. How do the central supermassive black holes (SMBH), ubiquitous in galaxies, get close to each other in a post-merger galactic nucleus? Do they ultimately coalesce under emission of gravitational waves? Some new answers to these questions will be presented, obtained by direct N-body modelling on new special supercomputers. We will see, how the stalling problem could be overcome to bring the SMBH binaries close enough together, that Newtonian dynamics breaks down.
The Post-Newtonian approximation for perturbed relativistic two-body systems allows to study the SMBH binary until coalescence in a finite time; from our simulations we directly and quantitatively predict gravitational wave emission for the LISA satellite. It will be shown why special instruments are required - special supercomputers for numerical modelling, and gravitational wave detectors, which need theoretically modelled signals and waveforms.
Recent progress and future plans to support our software and new hardware in national and internationale grid infrastructures are discussed. New benchmarks using graphical processing units (GPU, game cards) show that they are a very promising future tool for computational astrophysics in a much wider range of applications than before e.g. in the case of GRAPE.

2008 Apr 04 10:30 Marek Kowalski
(Humboldt Univ. Berlin)

Supernovae: from dark energy to neutrino astrophysics

The discovery of dark energy with type Ia supernovae has been followed by considerable observational activity to further constrain its properties. After a brief introduction to the field of observational cosmology I will review some of the current ongoing observational efforts. I will then present a new compilation of the available world's SNe data and discuss the current observational constraints on the properties of Dark Energy.
In the last part of the talk I will discuss a new project, which aims at the detection of high-energy neutrinos from core collapse SNe and GRBs. The project consists of complementing large neutrino telescopes (such as IceCube) with optical follow-up observations. By searching for rising SN lightcurves or GRB afterglows through optical follow-up observations, one can significantly improve the perspectives for the detection of such sources.

2008 Mar 28 10:30 Nathalie Toqué

Internal differential rotation for intermediate-mass stars

2008 Mar 14 10:30 Meghan Gray
(Univ. Nottingham)

STAGES: galaxy evolution in a supercluster environment

I will present results from a major multiwavelength endeavour to understand the large-scale structure and galaxy populations of the Abell 901/902 supercluster at z=0.165. The STAGES (Space Telescope A901/902 Galaxy Evolution Survey) team are using a 0.5x0.5 degree ACS/HST mosaic to measure detailed morphologies of the supercluster members, in addition to creating a high-resolution dark matter map from weak gravitational lensing. In addition, we are emplying extensive complementary observations from the X-ray to radio to fully understand the stellar masses, star-formation histories, and AGN content of the galaxies. Together with the maps of the dark matter, intracluster medium, and large-scale galaxy distributions, we aim to understand the influence of environment on galaxy evolution from the near-field to cluster cores.

2008 Feb 27 10:30 Scientific colloquium

Anlässlich der Emeritierung von Prof. Detlef Schönberner

11:00 Opening Matthias Steinmetz, AIP
11:05 Welcome addresses (Brigitte Klotz, MWFK; Klaus G. Strassmeier, AIP; Wolf-Rainer Hamann, UP)
11:30 Falk Herwig: Stellar evolution on and beyond the Asymptotic Giant Branch
12:15 Lunch buffet
13:15 Matthias Steffen: The evolution of planetary nebulae
14:00 Simon Jeffery: FG Sge - exposing a heresy
14:45 Coffee break
15:15 Ralf Napiwotzki: The blue straggler mystery
16:00 Ulrich Heber: Hydrogen-deficient stars

2008 Feb 08 10:30 Christer Sandin

The value of physical detail and numerical precision: How do steady dust-driven winds form?

In the final stages of stellar evolution low to intermediate mass stars lose their envelope in a strong stellar wind. Matter, which has been processed inside these stars, is thereby returned to the interstellar medium. In the wind acceleration region dust forms through a complex dynamic interaction with radiation and gas; such dust is also believed to drive the most massive winds on the asymptotic giant branch. After summarizing basic concepts of wind formation I will in this presentation demonstrate how new – numerically improved – wind models result in steady outflows, generally; and not irregular as before (cf. arxiv:0711.0281). Both for models that include gas-dust drift, and those which do not.

2008 Feb 01 10:30 Workshop

IT User Conference

2008 Jan 25 10:30 Ulrike Heiter
(Uppsala Univ.)

GAIA: physical parameters for one billion stars

GAIA is the ESA space astrometry mission due for launch in 2012. Its objective is to map a large part of our Galaxy and its surroundings by simultaneous positional, radial-velocity, and multi-colour photometric measurements. During a five-year period Gaia will survey approximately one billion Galactic stars, and detect and classify more than ten thousand extrasolar planets, as well as large numbers of Solar-System and extragalactic objects. It will also address questions of fundamental physics and cosmology. The data reduction for Gaia is entrusted to the Gaia Data Processing and Analysis Consortium (DPAC), involving nearly 300 scientists and engineers throughout Europe, including teams in Sweden. I will describe the science goals of Gaia and the work carried out in Uppsala within the DPAC Coordination Unit "Astrophysical Parameters". This includes calculating synthetic stellar spectra for algorithm development, obtaining ground-based observations for calibration and testing purposes, and improving the physics of stellar atmosphere models.

2008 Jan 18 10:30 Gherardo Valori

Reconstruction of magnetic fields in the solar corona

2008 Jan 11 10:30 Spyridon Kitsionas

Interstellar turbulence and star/planet formation

2007 Dec 14 10:30 Thorsten Ratzka

High spatial resolution observations of T Tauri stars

Although already proposed in the 19th century as a promising technique, stellar interferometry remained a tool with very limited applications. But after the first generation of VLTI instruments proved their potential, the situation is changing dramatically. Long baseline interferometry at optical wavelengths is becoming more and more a common tool to study a wide variety of astronomical objects.
After introducing the first scientific instrument on the VLTI, the MID-infrared Interferometric instrument (MIDI), examples of our work with MIDI that aims for the determination of the geometry and the dust properties of circumstellar discs around T Tauri stars will be presented.

2007 Dec 07 10:30 Alexander Warmuth

Particle acceleration and energy release in solar flares

The sun is the most energetic particle accelerator in the solar system. During solar flares, ions are accelerated to energies of up to tens of GeV, and electrons up to hundreds of MeV. The question of how these particles are accelerated is still one of the main unsolved problems in solar physics.
Observationally, the recent years have seen tremendous progress with the RHESSI (Ramaty High Energy Solar Spectroscopic Imager) hard X-ray satellite. Combined with radio and in-situ observations, these data have put a lot of constraints on the acceleration mechanism. One of the proposed mechanisms, shock drift acceleration, will be discussed in detail.

2007 Nov 30 09:30 Workshop

Science with STELLA

2007 Nov 23 10:30 Ralf-Dieter Scholz

Cool Subwarfs

2007 Nov 16 10:00 Thomas Rauch
(Eberhard-Karls-Univ. Tübingen)

Spectral Analysis of Extremely Hot Stars

Spectral analyses of hot, compact stars by means of non-LTE model-atmosphere techniques have arrived at a high level of sophistication. The accelerated lambda iteration method is a powerful tool to calculate line-blanketed atmospheres which include opacities of all elements from hydrogen up to nickel simultaneously. These kind of models is necessary for a reliable interpretation of stellar spectra from the infrared to the X-ray wavelength range.
In the framework of the German Astrophysical Virtual Observatory (GAVO) project, we provide synthetic spectra for hot stars in order to enable a VO user to perform spectral analysis without detailed knowledge of our code. We present examples for spectral analyses of hot stars with effective temperatures up to 1 MK.

2007 Nov 09 10:00 Festkolloquium Wempe Award

Ignasi Ribas

2007 Nov 02 10:30 Oliver Gressel

TurISM - direct simulations of the turbulent interstellar medium

Observations in polarized emission reveal the existence of large-scale magnetic fields in a wide range of spiral galaxies. Radio-polarization data show that these fields are strongly inclined towards the radial direction, with pitch angles as big as 35°, and thus cannot be explained by the action of differential rotation alone. Global dynamo models describe the generation of radial magnetic field from the underlying turbulence via the so called alpha-effect. However, these global models rely on crude assumptions about the small-scale turbulence. Model parameters and their functional dependence, if not neglected, are often chosen for practicability rather than on empirical grounds.
To overcome these restrictions we perform fully dynamical MHD simulations of interstellar turbulence driven by supernova explosions. Our local approach includes dissipative as well as radiative physics to properly model the multi-phase interstellar medium. From our simulations we extract profiles of the contributing diagonal elements of the dynamo alpha-tensor as functions of galactic height. Within the dynamo model these terms are responsible for the creation of ordered fields. We also measure the coefficients describing vertical expulsion of the created field and find that the ratio between these two effects has been strongly overestimated in earlier analytical work where dynamo action seemed highly impossible. Furthermore, we apply the recently suggested test field method to derive a quantitative measure of the turbulent resistivity which we find to be of the order of 10^27 cm²/s.

2007 Oct 26 10:30 Institute conference

Zentrum fuer Innovationskompetenz: innoFSPEC

2007 Oct 19 10:30 Horst Balthasar

The height dependence of the magnetic field in a sunspot

One important problem in solar physics is the magnetic coupling of the different atmospheric layers and the solar interior, but up to now it is even not clear how the magnetic field changes through the photospheric layers of a sunspot. Here I investigate a single sunspot observed in two different spectral lines at the VTT on Tenerife with high spatial resolution. Inverting the spectro-polarimetric data of the two lines separately, the properties of the magnetic vector field are determined for two different photospheric layers. A lower magnetic field strength and lower inclination of the magnetic field lines are found for the higher layer. Parameters derived from the magnetic vector field are also discussed.

2007 Oct 12 10:30 Achim Peters
(Humboldt Univ. Berlin)

Modern optical tests of Lorentz invariance

"The speed of light is finite and does not depend on the motion of either source or observer". This is the fundamental statement underlying Albert Einstein's theory of Special Relativity. First formulated early in the 20th century, this theory now is one of the cornerstones of our scientific understanding of the world and tightly woven into the fabric of modern physical theories. It also has become more and more relevant for daily life - timekeeping using modern atomic clocks and navigation using the global positioning system are just two examples. Due to this outstanding role, it always has been of prime importance to experimentally verify the validity of the underlying theory. Today, further incentive for such tests is provided by new theoretical attempts - such as string theory or loop quantum gravity - aiming at unifying the forces of nature, which indeed suggest small violations of Lorentz-Invariance.
This talk will discuss modern tests based on optical methods, which are especially well suited for the task at hand. A specific example is a modern version of the classic Michelson-Morley experiment testing the isotropy of light propagation, where the measurement is performed by monitoring the resonance frequency of an optical resonator continuously rotating on a precision turntable. This currently allows a sensitivity at the Delta c(theta)/c ~ 10^-17 level for a direction dependent variation of the speed of light, with the potential for improvements in precision by up to three orders of magnitude in the near future.

2007 Sep 14 10:30 Ignasi Ribas
(IEEC Barcelona)

Exoplanets and life

Research on exoplanets has become one of the most active subjects in Astronomy. Recent years have witnessed great progress instrumental capabilities resulting in now over 200 exoplanets discovered, mostly of Jupiter size but already reaching down to masses of just a few times that of the Earth. One of the major surprises with the improving statistics is how far was theory from predicting the existence of the objects we are detecting. Their orbital sizes, eccentricities or mass distributions are unlike those of Solar System planets. This raises a natural concern about the possible oddity of the Solar System among planetary systems in the Galaxy. Also, with the ever increasing instrumental power and time baseline, the question of planetary habitability and the existence of life beyond Earth becomes relevant. The quest for habitable planets in the solar neighbourhood promises to be one of the most exciting endeavours for science in the coming decades. In this talk I will give an overview of the current status in exoplanet research and point out some of the questions that remain still unanswered. Also, I will address habitability in an ample context and discuss future directions for research in this field.

2007 Aug 28 14:00 Colin Cunningham
(Royal Obs. Edinburgh)

Current Projects at the UK Astronomy Technology Centre

I will describe a range of projects we are working on, including the VISTA widefield IR survey telescope, KMOS - the multiobject IFU spectrometer for VLT, SCUBA 2 - the world's largest submm camera, and the mid IR instrument for the James Webb Space Telescope, MIRI. I will also talk about some of the projects funded by the EU Framework Programme.

2007 Jul 27 10:30 Dieter Breitschwerdt
(Vienna Univ.)

Dynamical Evolution of a Supernova Driven Turbulent ISM

The interstellar medium (ISM) in late-type galaxies is a multicomponent system consisting mainly of a compressible fluid (supplemented by dust), permeated by magnetic fields and relativistic particles and ionized by stellar photons. Regarding the energy input into the ISM of actively star forming galaxies, supernova (SN) explosions, and to a lower degree stellar winds and photons, have emerged as dominant sources, driving ISM evolution and structure. The inherent complexity and nonlinearity of the system require a careful approach, especially for advanced numerical 3D parallel computer simulations. We have built a bottom-up model of a turbulent SN driven ISM over the last years (EVAF = Evora-Vienna Astrophysical Fluid Code), emphasizing the necessesity of critical numerical resolution appropriate for the physical processes included, and for sufficiently long evolution times for a dynamical equilibrium to be established. It is demonstrated that both for hydro- and magnetohydrodynamical simulations the distribution of the plasma into "stable" phases is different from standard models, and that even a considerable fraction of the gas mass resides in classically unstable phases. It is further shown that turbulence has a significant influence on the structure and the evolution of the ISM. Finally, I will compare results to current observations, and give a progress report of ISM modeling.

2007 Jul 06 10:30 Tae-Sun Kim

The thermal history of the intergalactic medium

The standard big bang model predicts that the primordial hydrogen (H) and helium (He) comprising the intergalactic medium were highly ionised in the Early Universe, but became almost completely neutral at redshifts z~1000 due to the adiabatic cooling by Hubble expansion. Given that the intergalactic medium is mostly ionised at z < 6, two of the major questions in cosmology arise: 1) When were hydrogen and helium reionised? and 2) Which sources dominated this reionisation process, stars or AGNs? The recent WMAP results suggest that the reionisation of neutral hydrogen (HI -> HII) and neutral helium (HeI -> HeII) occurs at z~10, while the reionisation of singly ionised helium (HeII -> HeIII) is rather controversial. Roughly speaking, the HeII reionisation provides an extra heating source to the intergalactic medium, thus increasing the temperature of the latter. Lyman-Alpha forest observed in high-redshift QSOs provides a probe of the thermal evolution of the intergalactic medium, since its physical properties depends on the reionisation history. Here, I review basic physical theories and contradictory observations on the thermal evolution of the intergalactic medium and the future works to be done.

2007 Jun 22 10:30 Marcus Brüggen
(Int. Univ. Bremen)

The answer is blowing in the wind - The AGN-ICM connection

Recent observations show a multitude of physical effects that occur when active galactic nuclei (AGN) interact with the ambient intracluster medium (ICM). The interaction between AGN and the ICM is essential for understanding feedback, which is believed to be the crucial ingredient for the baryonic part of galaxy formation. In recent years, simulations of the interaction between active galactic nuclei and the intracluster medium have become increasingly realistic and sophisticated. Most hydrodynamical simulations are now three-dimensional, some simulations have started to explore the effects of conductivity, viscosity and magnetic fields. The latest generation of simulations start from realistic cluster environments taken out of cosmological simulations. In this talk, I wish to review recent advances in our understanding of how the AGN interacts with the ICM. New observational results and the latest simulations of the AGN - ICM interaction will be shown.

2007 Jun 15 10:30 Jörn Wilms
(Dr.-Remeis-Stw. Bamberg / Univ. Erlangen)

X-ray and Gamma-ray observations of Galactic Black Holes

Long term monitoring of Galactic Black Hole candidates over the past 10 years with instruments such as the Rossi X-ray Timing Explorer and the Ryle radio telescope, as well as supplemental observations with "large satellite observatories" such as Chandra, XMM-Newton, and INTEGRAL, have provided a wealth of information about the behavior of these sources throughout the electromagnetic spectrum on timescales from seconds to years. In particular, through the detection of relativistically broadened fluorescence lines these observations have provided strong evidence for the existence of relativistic motion as expected around a black hole. Furthermore, observations of the joint radio-X-ray behavior have challenged the traditional picture of thin disk accretion plus Comptonization in these systems, with emission from a (relativistic) outflow now being a potential contributor to the overall source luminosity. Concentrating in particular on the canonical black hole candidate Cygnus X-1, I will discuss observational results from monitoring campaigns in light of models for the accretion mechanism of the source, using both the standard Comptonization paradigm as well as new models in which the broad band spectrum of black holes is explained by the presence of an outflow.

2007 Jun 08 10:30 Romeel Dave
(Univ. Arizona)

The Impact of Galactic Outflows Across Cosmic Scales

Feedback from supernova-driven winds is an important driver of galaxy evolution, particularly during the heydey of star formation in the universe. I will present new cosmological SPH simulations incorporating heuristic models of superwind feedback, and study their impact on the properties of galaxies and intergalactic gas during the heydey of galaxy formation at z~2-6. I will focus particularly on metal enrichment as a unique observational tracer of such outflows. Remarkably, by parameterizing the outflow properties of galaxies at those epochs based on what is seen in local observations of rare starbursts, it is possible to reproduce a wide range of galaxy and IGM metallicity observations. I will further show that such agreement is unique to a rather narrow class of outflow models. Our simulations yield new and non-conventional interpretations for several puzzling observations, such as the constancy of CIV absorption in the high-z IGM, and the low scatter, uniformity, and slow evolution of the galaxy mass-metallicity relation. Our results suggests a strong connection between galactic outflows from the reionization epoch until today, and offer promise that this major uncertainty in galaxy formation theory will soon be well-constrained.

2007 Jun 05 16:00 Ehrenkolloquium

Zum 80. Geburtstag von Prof. Fritz Krause

2007 Jun 01 10:30 Michael I. Andersen

Gamma-ray bursts in the SWIFT era

2007 May 25 10:30 Simon Glover

The Second Stars

2007 Apr 27 10:30 Andreas Korn
(Uppsala Astr. Obs.)

The cosmological lithium discrepancy

I will review our recent efforts to scrutinize the importance of diffusive processes in altering the chemical composition of long-lived solar-type stars. By analysing unevolved and evolved stars in a nearby globular cluster, we were able to show for the first time that there are general atmospheric trends of abundance with evolutionary stage, in quantitative agreement with the most recent diffusion models. This finding has implications for early cosmochemistry and stellar age determinations. Moreover, it helps to understand why the amount of lithium in the atmospheres of old stars is seemingly lower than that known to be produced in the Big Bang (Nature 442, 657).

2007 Apr 20 10:30 Rob Piontek

Star Formation, Turbulence, and the Magnetorotational Instability in the Interstellar Medium

In this talk I will review the development of the classical theory of global star formation rates in spiral galaxies. Central to this theory are observations of a turbulent interstellar medium (ISM). In the standard view of the ISM this turbulence is attributed to explosions of supernovae (SNE). I will try to convince you that there are likely other important sources of turbulence in the ISM besides SNE, and that one of the possibilities is the magnetoroational instability (MRI). I'll explain how the MRI works, and report on our simulations which attempt to address the question of whether or not the MRI is important in the context of the ISM.

2007 Apr 11 10:30 Amri Wandel
(Hebrew Univ. of Jerusalem)

Massive Black Holes in Active Galactic Nuclei

In the last decade astronomers succeeded to detect Super-Massive Black Holes (SMBHs) in the centers of many nearby galaxies and to measure their masses. Three decades earlier SMBHs were postulated in Active Galacic Nuclei (AGN) - Seyfert galaxies and quasars. The masses of SMBHs in AGN are estimated by a variety of techniques, the most accurate of which is light-echo or reverberation mapping.
SMBH-masses of ordinary galaxies show a strong correlation with the luminosity of the host galaxy. The mass of the BH is a small fraction (0.001-0.003) of the host galaxy. We find that Black Holes of AGN follow the same BH-bulge relation as ordinary (inactive) galaxies. Curiosly a subgroup (Narrow Line AGN) seems to deviate from the universal value having a lower BH to bulge mass fraction.

2007 Mar 23 10:30 Manfred Küker

Solar and stellar differential rotation

2007 Mar 09 10:30 Moira Jardine
(Univ. St. Andrews)

Reaching out to the masses: the coronae and disks of T Tauri stars

Recent results from X-ray surveys of star-forming regions and from mapping the surface fields of T Tauri stars have begun to change our understanding of the way in which young stars accrete material from (and exchange angular momentum with) their disks. I will review the recent observational and theoretical results in this area and discuss promising new avenues of research.

2007 Mar 02 10:30 Workshop

Career Counselling II

10:30 - 11:00 coffee; 11:00 - 11:05 general introduction;
11:05 - 12:00 "Strategies to get a postdoc position (including guidance for application procedures)";
12:00 - 13:00 LUNCH BREAK;
13:00 - 14:00 "How and where to apply for grants (especially to fund my own position)";
14:00 - 15:00 "How does tenure-track work?"

2007 Feb 16 10:30 Gabor Worseck

The intergalactic UV background and the transverse proximity effect

After the epoch of reionization, the intergalactic hydrogen and helium is kept highly ionized by the ambient UV background generated by quasars and star-forming galaxies. The remaining tiny neutral fraction of hydrogen gives rise to the Lyman alpha forest observable towards high-redshift quasars. A quasar can locally increase the UV radiation field in its vicinity. This so-called proximity effect has been found with high statistical significance. However, foreground quasars ionizing other lines of sight to background sources have generally not been reported in the literature. By comparing the intergalactic Lyman alpha absorption of HI and HeII one can estimate the spectral shape of the UV background. Analyzing the variations of the UV spectral shape on two lines of sight, we have found evidence for a hard ionizing radiation field near the two background quasars and 7 foreground quasars. Since only quasars can produce the observed hard radiation, we interpret this as a signature of the transverse proximity effect.

2007 Feb 09 10:30 Silva Järvinen

Solar analogues

2007 Feb 02 10:30 Henk Spruit
(MPA Garching)

The 3D structure of sunspots

Our understanding of the physics of sunspots is currently in a state of very rapid progress. High resolution (0.1-0.2") observations with the Swedish 1-m Solar Telescope on La Palma indicate that the basic sub-surface structure (both of the umbra and the penumbra), is one of narrow field-free gaps between strong magnetic flux bundles. The gaps close around the visible surface. By a remarkable convergence of developments, this very structure is now reproduced also by ab-initio 3-D radiative MHD simulations. The talk will address some of the (previously puzzling) observational phenomena involved and their physical interpretation.

2007 Jan 26 10:30 Yago Ascasibar

What is Dark Matter?

In this talk I will try to convince you that dark matter might be not so dark after all. I will start with a short review of astrophysical evidence for dark matter, and an even shorter list of possible candidates. Then I will discuss several observable signatures of the decay or annihilation of dark matter particles, as well as the feasibility of detecting them with current and forthcoming instruments, from radio frequencies to gamma rays. I will also consider the distribution of dark matter within haloes and the impact of dark matter annihilation on galaxy formation and evolution.

2007 Jan 19 10:30 Detlef Elstner

Galactic Dynamos

2007 Jan 08 10:30 Institute conference

Evaluierung 2007

2006 Dec 15 10:30 Manfred Schüssler
(MPS Katlenburg-Lindau)

Simulation of solar magneto-convection

The interaction between convective flow and magnetic field is a key process of general astrophysical relevance. The near-surface layers of the Sun provide the unique possibility to study this process on its intrinsic spatial and temporal scales. Numerical 3D radiative MHD simulations have developed into a crucial tool for the interpretation of high-resolution observations in terms of the underlying physical processes. The talk will give a brief overview of selected results obtained with the MURaM (MPS/Univ. of Chicago Radiative MHD) code since the code became operational in 2003. The focus will be upon the most recent results. In particular, the following topics will be discussed:
- magneto-convection from quiet Sun to strong plage,
- pores and sunspot umbrae,
- emergence of magnetic flux,
- decay of mixed-polarity flux,
- surface dynamo action.

2006 Dec 08 10:30 Institute conference


2006 Dec 01 10:30 Henry Aurass

Diagnostics of SEP (solar energetic particle) injection and space weather physics

2006 Nov 24 10:30 Heidi Korhonen

Observations and dynamo theory

2006 Nov 17 10:30 John Kormendy
(Univ. of Texas, Austin)

Families of elliptical and spheroidal galaxies: wet versus dry mergers as the origin of the two kinds of elliptical galaxies

New surface photometry of all known elliptical galaxies in the Virgo cluster is combined with published photometry to derive composite brightness profiles over large radius ranges. They give enough radial leverage to show that Sersic functions describe nearly all ellipticals remarkably well. Therefore we can confidently identify central departures from these profiles that are diagnostic of galaxy formation:
Two kinds of departures are seen. Bright ellipticals (M_B < -20) have cuspy cores - "missing light" at small radii. Cores are well known and are naturally scoured by binary black holes produced in dissipationless ("dry") galaxy mergers. Faint ellipticals do not have cores; instead, they have extra light at the center above the inward extrapolation of the outer Sersic profile. The properties of the extra light resemble those of compact central components predicted in numerical simulations of mergers that contain gas. We suggest that faint ellipticals were produced by dissipational ("wet") mergers including central starbursts. Wet and dry mergers, respectively, explain how the observed dichotomy between faint-disky-coreless ellipticals and bright-boxy-core ellipticals was formed.
Why wet and dry mergers formed the dichotomy became clearer at the recent Potsdam Thinkshop on Black Holes and Galaxy Formation. This was a watershed in establishing the importance of energy feedback from active galactic nuclei (AGNs) into the galaxy formation process. The essential point is that hot, x-ray-emitting gas is required to store AGN energy and make it available to solve a variety of problems in galaxy formation. Remarkably, faint-disky-coreless ellipticals do not contain hot gas halos, while bright-boxy-core ellipticals do contain such halos. We suggest that AGN feedback in giant but not faint ellipticals explains why the E-E dichotomy arose.
Finally, we verify that there is a dichotomy between elliptical and spheroidal galaxies. Their properties are consistent with our understanding of their different formation processes: mergers for ellipticals and conversion of late-type galaxies into spheroidals by environmental effects and by energy feedback from supernovae.

2006 Nov 10 10:30 Rachel Somerville
(MPIA Heidelberg)

The mass assembly and star formation history in the Universe from z~6 to the present

Multiwavelength surveys like SDSS, GEMS, GOODS, DEEP/AEGIS and the UDF have allowed us to probe the physical properties of galaxies, such as their star formation rates and stellar masses, over a large fraction of cosmic history. I will highlight some of the recent results from these surveys, and discuss how well the view of the history of the assembly of galaxies in the "real Universe" agrees with the picture painted by the current generation of hierarchical models.

2006 Oct 27 10:30 Ana Monreal Ibero

Ultra-Luminous Infrared Galaxies

2006 Oct 20 10:30 Michael Weber

Differential Rotation and Meridional Flow on Giant Stars

2006 Oct 13 10:30 Wolfgang Gieren
(Univ. Concepción, Chile)

The Araucaria Project: measuring improved distances to nearby galaxies

2006 Oct 06 10:30 Eva Grebel
(Uni Basel, AIP)

Near-field Cosmology with the Local Group

2006 Sep 29 10:30 Arman Khalatyan

Disk Galaxy Formation in Cosmological Environment

2006 Sep 22 14:00 Carsten Denker
(Big Bear Solar Obs.)

High-Resolution Observations at BBSO - First Steps Towards the New Solar Telescope

The New Solar Telescope (NST) project at Big Bear Solar Observatory (BBSO) now has all major contracts for design and fabrication in place and construction of components is well underway. The NST is collaboration between BBSO, the Korean Astronomical Observatory (KAO) and Institute for Astronomy (IfA) at the University of Hawaii. The project will install a 1.6 meter, off-axis telescope at BBSO, replacing a number of older solar telescopes. The NST will be located in a recently refurbished dome on the BBSO causeway which projects 700 meters into the Big Bear Lake. In the first part of the talk, I will provide a description of the optical design, the thermal control of the new dome, the optical support structure, the telescope control systems, active and adaptive optics systems, and the post-focus instrumentation for high-resolution spectro-polarimetry. The second part of the talk focuses on high-resolution observations of solar active region NOAA 10756 obtained on 2005 May 2 with the 65 cm vacuum reflector at BBSO. Time-series of speckle reconstructed white-light images and two-dimensional spectroscopic data are combined to study the temporal evolution of the three-dimensional vector flow field in a delta sunspot group. Recent instrumentation upgrades, including high-order adaptive optics, a Fabry-Perot-based two-dimensional imaging spectrometer, and high-speed CCD cameras for image restoration, enabled us to obtain an hour-long data set of consistent high quality. We focus on flows surrounding the delta configuration with special emphasis on shear flows associated with the magnetic inversion line.

2006 Sep 22 10:30 Nick Kaiser
(Univ. Hawaii)

Probing Dark Matter with Weak Lensing

Weak lensing uses the distorted shapes of distant galaxies to probe the distribution of dark matter along the line of sight. In this talk I will first give a brief review of the early history of the subject. I will then review the theoretical background for light deflection in a lumpy universe and how the observed polarization of galaxy shapes can be used to reconstruct the 2-dimensional projected mass density and to derive the statistical properties of the mass density field such as the power spectrum. I will show examples of weak lensing analyses that reveal the distribution of dark matter in galaxy halos; in galaxy clusters and on supercluster scales. I will conclude with a discussion of the near term future prospects for weak lensing.

2006 Sep 15 10:30 Matthias Steinmetz

Dark energy

2006 Sep 08 10:00 Festkolloquium Wempe Award

2006 Aug 07 13:30 Steven S. Vogt
(Lick Obs., Univ. California, Santa Cruz)

10 years of planet hunting at Lick Observatory

I give a brief summary of our results from the past 10 years of planet hunting/finding, and also an update on our new 2.4-m Automated Planet Finder that we hope to commission later this year, as well as my plans to instrument a 30-m telescope to find habitable earths.

2006 Jul 07 10:30 Hans-Erich Fröhlich

Bayesian period search

2006 Jun 30 10:30 Christian Vocks

Plasma kinetics in the solar corona and chromosphere - new insights with GREGOR

2006 Jun 23 10:30 Gwendolyn Meeus

Disc and dust evolution around young (< 10 Myr) stars

During the last 10 years, our knowledge about circumstellar discs and dust has increased dramatically. In this talk, I will focus on what we know about the discs of young stars through infrared observations, mainly spectroscopy. After a short introduction, we will concentrate on Herbig Ae/Be stars. I will discuss current disc models that explain their spectral energy distributions. Infrared spectra will be interpreted in terms of dust properties, which in turn will be linked to the disc models proposed. With the same approach I will give an overview of the discs of the less massive T Tauri stars. To round off, we will glance at the most recent results for brown dwarf discs, so that the whole range from substellar to a few solar masses will be covered. To conclude, I will indicate future directions in which to continue this work.

2006 Jun 16 10:30 Thomas Lohse
(Humboldt Univ. Berlin)

Astrophysics and Particle Physics of Very High Energy Cosmic Rays

Almost a century after their dicovery by Victor Hess, the origin of cosmic rays is still far from understood. The composition and spectral behaviour of cosmic rays at very high energies is not well known, the cosmic ray sources have not yet been convincingly identified and experimental information is insufficient to fully understand the acceleration of cosmic rays in source candidates and the propagation through the interstellar and intergalactic medium. Also, dark matter annihilation, the decay of superheavy relic-particles from the big bang and other exotic origins are possibly responsible for at least part of the cosmic rays.

Very high energy cosmic rays are measured directly by detection of the extensive air showers they induce when interacting in the atmosphere. Source locations and acceleration mechanisms, however, can best be revealed by measuring high energy photons or neutrinos which are thought to be produced in interactions of charged cosmic rays in the ambient medium of the sources. A broad experimental program is ongoing, exploiting various kinds of messenger particles, hadrons, gamma rays, and neutrinos. The status and some recent results will be reviewed.

2006 Jun 09 10:30 Sandra Jeffers
(Lab. Astroph. Toulouse-Tarbes)

The enigmatic eclipsing binary SV Cam as observed by the Hubble Space Telescope

Spectrophotometric data from 9 HST orbits, observed in November 2001, have been used to eclipse-map the primary component of magnetically active RS CVn SV Cam. In combination with its HIPPARCOS parallax it is found that the surface flux is lower than computed from the best fitting PHOENIX model atmosphere. This flux deficit can only be accounted for if about a third of the primary's surface is covered with approximately 30% unresolved spots and a large polar cap of approximatemy 45° in diameter. I show that this spot coverage has important implications for the determination of the binary's system parameters. I also investigate the reliability of image reconstruction based on Chi-square minimisation of stars with high unresolvable spot coverage.

2006 Jun 02 10:30 Institute conference


2006 May 24 09:00 Workshop

Science with Supercomputers

The AIP has hosted powerful supercomputers solely dedicated to astrophysics for several years. It is about time to reflect upon the benefits of having in-house access to such systems and to make efforts to improve upon the utilization of parallel computers. During this one-day workshop we like to learn about the science done employing the AIP supercomputer as well as discussing perspectives and future needs. While the main emphasis will be on "science" rather than "numerics" we also like to reserve a session to discourse on coding and performance issues.

2006 May 12 10:30 Workshop

Career Counselling

During the meeting, a handful of short presentations will be given, describing some of the more important academic systems around the world, as well as funding sources. Each presentation will also give a 'personal' view of what it takes to make a scientific career in the world of Astronomy/Astrophysics.

2006 May 5 10:30 Asmus Böhm

What observations tell us about disk galaxy evolution

Focussing on results from my own work and collaborations I am involved in, I will give an overview of disk galaxy evolution over the last 8 Gyr (redshifts 0<z<1) from an observer's point of view. Scaling relations will be used to quantify fundamental galaxy parameters at different cosmic epochs. One of the most interesting findings is that the stellar populations in disks seem to evolve anti-hierarchically, a phenomenon previously refered to as 'down-sizing'.

2006 Apr 28 10:30 Serge Correia

Studying young stars with the VLT Interferometer

2006 Apr 21 10:30 Rainer Arlt

How magnetic is the solar tachocline?

2006 Apr 07 10:30 Natalie Krivova
(MPS, Katlenburg-Lindau)

Solar magnetism and irradiance variability

Measurements of solar irradiance have revealed its variability at different time scales from minutes to decades. About 90% of these variations are reproduced by recent models assuming evolution of the solar surface magnetic fields being their main cause. The observations, however, do not provide any information on longer-term secular trends. The stellar evidence for such a change is now subjected to question, and its magnitude might have been overestimated. Once good understanding of the directly observed variations has been gained, we can also attempt to carry out an analysis of variations of the surface magnetic flux and solar irradiance on longer time scales and extend the models back in time. A brief overview of our recent efforts to reconstruct solar total and spectral irradiance on time scales of days to centuries will be given.

2006 Mar 31 10:30 Rosa Dominguez Tenreiro
(Universidad Autonoma de Madrid)

Elliptical galaxy formation from cosmological hydrodynamical simulations

2006 Mar 17 10:30 Ed Salpeter
(Cornell Univ., Ithaca)

High velocity clouds and dwarf galaxies

2006 Mar 10 10:30 Axel Schwope

Isolated neutron stars

ROSAT has discovered the new class of X-ray dim isolated neutron stars (INS). Despite the expected many thousands there are now just 7 confirmed objects. Ground- and space-based follow-up with Chandra and XMM-Newton have revealed their main properties (temperature, spin, proper motion, birth place, magnetic field, distance). I describe those observations and implications for the still unknown equation of state and discuss them in the context of the general NS population.

2006 Mar 03 10:30 Rainer Beck
(MPIfR, Bonn)

Magnetic Fields in Spiral Galaxies

The strength and structure of interstellar magnetic fields can be studied by observations of radio continuum emission, its polarization and its Faraday rotation. Fields with a well ordered spiral structure exist in grand-design, barred, flocculent and even irregular galaxies. Total field strengths in spiral arms and bars 10-30 MicroGauss. In spiral galaxies the fields are aligned parallel to the optical spiral arms, but the strongest regular fields are found in interarm regions, sometimes forming ``magnetic spiral arms'' between the optical ones. While the turbulent field is compressed in the spiral arm or bar shock, the regular field decouples from the cold gas and is hardly compressed. Within spiral arms with massive star formation, field lines are tangled so that very little polarization is observed. Faraday rotation of the polarization vectors reveals patterns which are signatures of coherent large-scale fields in galactic disks generated by dynamos. The majority of field structures in galaxies requires a superposition of dynamo modes. Dynamos are also operating in circumnuclear regions. Magnetic stress may drive inflow of gas towards the nucleus.

Magnetic fields are observed in galactic halos at large distances from the disks. The largest halos and strongest fields result from galactic winds, from interaction, or from ram pressure in an intercluster medium.

Present-day radio polarization observations are limited by sensitivity. Next-generation radio telescopes (LOFAR and the Square Kilometer Array) will be able to reveal the full wealth of magnetic structures in galaxies.

2006 Feb 24 10:30 Karl Gebhardt
(Univ. Texas)

Black Holes of All Masses: Understanding the Fundamental Correlations

Recent observational and theoretical work suggest that black holes are essential components of galaxies. In fact, they may be one of the keys to understanding how galaxies form and evolve. I will give a general overview of the observational results for black holes in galaxies, including discussion of their effects on the stellar orbital distribution. I will focus the talk on the two extreme mass ranges, from whether globular clusters contain black holes up to black holes in brightest cluster galaxies. The present results suggests that the black hole correlations span over seven orders of mass. This concordance suggests a more intimate connection between these different types of systems than what has previously been thought. I will also discuss the future of black hole studies, from space and from the ground.

2006 Feb 17 10:30 Jens Niemeyer
(Univ. Würzburg)

The Birth, Life, and Death of Thermonuclear Flames in Type Ia Supernovae

Multidimensional simulations of exploding Chandrasekhar mass white dwarfs so far have concentrated on the propagation of thermonuclear flames and detonations using simple assumptions about their ignition and survival. Recent studies have shown that the location and structure of igniting flames can have a strong impact on the global parameters of the explosion. Furthermore, the behavior of detonations propagating through an inhomogeneous medium of partially burned material has been analyzed. The current state of these investigations will be presented.

2006 Feb 10 10:30 Hermann Boehnhardt
(MPS Katlenburg-Lindau)

The Kuiper Belt - Fridge at the Edge of the Planetary System

In 1992 the discovery of the Kuiper Belt started with a more than 60 years delay. In the meanwhile more than 1000 objects were found orbiting the Sun beyond Neptune at the edge of the planetary system. The Kuiper Belt appears to be a graveyard of planetesimals in our own solar system, providing surprising "messages in a bottle" on the early history of the formation of the planetary system. The talk outlines our current and still growing understanding on the dynamical structure of the belt, the physical properties of the bodies therein, how they are connected to the planetary system formation and related to other icy bodies like comets.

2006 Feb 03 10:30 Arnaud Siebert

The Radial Velocity Experiment (RAVE)

RAVE is an ambitious spectroscopic survey to measure radial velocities and stellar atmosphere parameters (temperature, metallicity, surface gravity) of up to one million stars using the 6dF multi-object spectrograph on the 1.2-m UK Schmidt Telescope of the Anglo-Australian Observatory (AAO). RAVE will provide a giant leap forward in our understanding of our own Milky Way galaxy, providing a vast stellar kinematic database larger than any other survey proposed for this coming decade.

The first data release, containing over 25,000 radial velocities, is scheduled in early february 2006 (less than a week from now). I will describe its content as well as the general properties of the survey that will extend over the next few years. A brief summary of the first scientific results, making use of those data, will be given.

2006 Jan 27 10:30 Moshe Elitzur
(Univ. Kentucky and LAOG, Grenoble)

The AGN obscuring torus - is it really a "bagel"?

The variety of observations of Active Galactic Nuclei (AGN) have been classified with a simple unified scheme: The nuclear activity is powered by a central massive black hole that drives radio emitting jets and ionizes surrounding line-emitting clouds. The whole system is surrounded by a dusty torus and the observer's orientation with respect to this obscuring torus determines the appearance of the AGN. Pole-on viewing gives rise to superluminal jets and Seyfert 1 line spectrum, edge-on results in extended radio lobes and Seyfert 2 lines. The torus is comprised of optically thick dusty clouds in a rotating configuration with roughly equal vertical and radial dimensions.

Although the observed IR is in broad agreement with the expected effects of the dusty torus, detailed properties of the spectral energy distribution (SED) posed difficult problems. The dynamical origin of the rotating cloud configuration, and especially its vertical support, present an even more serious challenge. We have recently developed a formalism to handle radiative transfer in clumpy media and in this talk I show that the SED problems find a natural explanation if the dust is contained in about 5--10 clouds along radial rays through the torus. Furthermore, the properties of the model SED may also provide the answer for the torus dynamical origin.

2006 Jan 20 10:30 Institute conference


2006 Jan 13 10:30 Ralf Klessen

Star Formation

All stars in our Galaxy form in cold interstellar clouds of molecular hydrogen. These molecular clouds (MCs) form by convergent motions in the warm, magnetically subcritical, atomic gas, driven by self-gravity and interstellar turbulence. As the gas is dynamically compressed, it cools and becomes overpressured, molecular, self-gravitating, and roughly magnetically critical. The dynamical processes associated with molecular cloud formation give rise to strong internal turbulence, supersonic with respect to the cooled compressed gas. Turbulent density fluctuations substantially speed up molecule formation. Dynamically, this turbulence plays a dual role.

On global scales it provides support against collapse; on small scales it promotes local collapse. The mass scale for the smallest gravitationally collapsing clumps may be determined by the length scale at which the velocity dispersion becomes subsonic. Molecular clouds as well as their internal structures appear to be transient, with lifetimes comparable to their local dynamical timescales. Numerical simulations that suggest the star formation efficiency depends nonlinearly on the mean field strength and decreases with the ratio of turbulent to gravitational energy in the clouds. Radiation and winds from the newly formed stars dissociate and disrupt nearby molecular gas, but also accelerate collapse by sweeping up dense shells of gas. The stellar mass spectrum is determined by the complex interplay between turbulent molecular cloud structure (as initial condition for gravitational collapse), the subsequent protostellar accretion (which again is influenced by the turbulent cloud environement) and possible stellar-dynamical effects in the nascent embedded star cluster (like ejection from multiple systems during the main accretion phase).

I will review recent advances in dynamical star formation theory on large as well as on small scales and discuss results from numerical calculations of gravoturbulent cloud fragmentation and early evolution of embedded nascent star clusters.

2006 Jan 06 10:30 Bernhard Kliem

The physics of solar eruptions

2005 Dec 21 11:00 Rolf Kudritzki
(Inst. for Astronomy, Hawaii)

Exploring the transient universe with Pan-STARRS

2005 Dec 16 10:30 S. Lilly
(ETH Zürich)

The COSMOS and zCOSMOS surveys

Despite major progress in the last decade in characterising the galaxy and AGN populations over 90% of the lifetime of the Universe, there is still a lot of uncertainty concerning the physical processes that have actually driven the evolution of galaxies over this time span. Several arguments suggest that the environment of galaxies may be playing a major role in this process. Unfortunately very little is known systematically about the environments of galaxies at high redshifts. The international 2degree2 COSMOS project aims to understand the three way relationships between the evolution of galaxies, their central active nuclei and their environments on scales from the immediate 100 kpc group environment up to the 100 Mpc scales of the cosmic web. The 40,000 galaxy zCOSMOS redshift survey which is now underway with the ESO VLT will play a central role in this effort. In this talk I will motivate and describe the COSMOS and zCOSMOS projects and conclude with a brief preview of results from some of the Z(ürich)-COSMOS work being done at ETH.

2005 Dec 14 11:00 Falk Herwig
(Los Alamos National Laboratory)

Stellar Hydrodynamics and Nuclear Astrophysics

I will present the first multi-dimensional hydrodynamic simulations of He-shell flash convection. He-shell flashes are the main engine for nucleosynthesis in low- and intermediate mass giants. Theses flashes drive low Mach number convective flows, which provides mixing, e.g. for the slow neutron capture nucleosynhesis. Convection excites a rich spectrum of internal gravity waves in the stable layers both above and below the convection zone. Actual penetration of convective motions into the stable layers is very small. However, the analysis of oscillation properties indicates that both gravity modes and convective motions cross the convection boundary. I will sketch future work in this project, including preliminary results on the extension of these simulations to reactive-convective flows. Finally, I will briefly comment on implications of the simulations for nuclear astrophysics applications.

2005 Nov 25 10:30 Andrea Cattaneo

Self-regulated black hole growth in a quiescent galaxy

2005 Nov 21 15:00 Alexander Kosovichev
(Stanford Univ., AIP)

Diagnostics of Sunspots and Active Regions by Local Helioseismology

New methods of `local' helioseismology, time-distance helioseismology, ring-diagram analysis and acoustic holography provide 3D maps of variations of the sound speed and mass flows below the solar surface. I will discuss recent advances in these techniques, and their application to imaging of emerging magnetic flux, evolving active regions, studying the dynamics of sunspots, and the relationship of subphotospheric processes to magnetic energy build-up and release in the solar atmosphere and corona.

2005 Nov 18 10:30 Peter D. Barthel
(Kapteyn Institute, Groningen)

To be or not to be active - the occurrence of nuclear activity in galaxies

The occurrence and driving force of nuclear activity in galaxies is examined, using samples of nearby objects. Investigations at radio-wavelengths provide a reliable AGN census, whereas optical integral field data yield intriguing information concerning the AGN mechanism. Evidence for an AGN-starformation symbiosis will be addressed.

2005 Nov 16 10:00 Alexander Kosovichev
(Stanford Univ., AIP)

Helioseismology of the Global Structure and Dynamics of the Sun

Global helioseismology of the Sun based on accurate measurements of multiplets of resonant oscillation modes. The mean frequencies and frequency splitting of these multiplets are used in helioseismic inversion procedures to determine the radial stratification, asphericity and differential rotation of the Sun. Almost 10 years of continuous observations of solar oscillations from SOHO and GONG provided unprecedented view of the changing with the 11-year cycle solar interior and important clues for understanding the solar dynamics and dynamo.

2005 Nov 11 10:30 Institute conference


2005 Nov 04 09:30 Wempe Prize award to Alexander Kosovichev
(AIP, Stanford Univ.)

Wempe Prize colloquium

2005 Oct 28 10:30 Alexander Kosovichev
(Stanford Univ., AIP)

Sunquakes and Helioseismology

Observations of solar oscillations provide powerful diagnostics for probing the Sun's interior. I will discuss the basic principles of helioseismology, and present recent observational results from the SOHO space mission and ground-based network, including the internal structure and chemical composition, differential rotation, meridional circulation, structure and dynamics of sunspots and active regions. I will also present new observations of `sunquake' events produced by solar flares, and discuss their relation to the flare energy release, and helioseismic diagnostics of flaring active regions.

2005 Oct 14 10:30 Matthias Hoeft
(Int. Univ. Bremen)

How to avoid dwarf galaxy formation

2005 Sep 09 10:30 Ralph Neuhäuser
(Univ. Jena)

Direct imaging of young sub-stellar companions - brown dwarfs and planets

We will present and discuss our recent and new results on direct imaging searches for planetary companions around young nearby stars, in particular the GQ Lupi system, for which new data will be shown. The companion to GQ Lupi shares the proper motion of the primary star and shows a late spectral type (early L). It will also be discussed whether the companion is really bound and whether the system is long-term stable. The most important question then is the mass of the companion, how well it can be determined and whether it is below or above the Deuterium burning minimum mass of 13 Jupiters separating planets and brown dwarfs. We will discuss the question whether the companions to GQ Lupi as well as to 2M1207 and AB Pic are either brown dwarfs or planets, and will in particular suggest observations for the near future (few years) that can distinguish between the two alternative (brown dwarf or planet), based mostly on gravity and metallicity.

2005 Jul 29 10:30 Klaus-Peter Schröder
(Univ. of Sussex)

Do we finally understand the mass-loss of cool stellar winds (not driven by dust)?!

Dedicated to the 30th anniversary of the "Reimers law"

Since 30 years, Reimer's well-known relation for the mass loss rate of ordinary cool stellar winds has been used. Although it seems to give approximately the right rates, the Reimers relation has never been understood in a physically meaningful way, and its scaling parameter eta seems to depend on the type of giant. - We here discuss a simple physical model of the wind which leads to an improved version of the Reimers law, with a universal eta value (calibrated precisely with the RGB mass loss found in globular clusters observed with HST). Finally, we can explain, why the Reimers relation comes close to the right rates, and we resolve the "second parameter problem" of Horizontal Branch in globular clusters in a natural way.

2005 Jul 22 10:30 Sanjib Sharma

Angular Momentum Distribution and Phase Space Structure of Galactic Halos

The standard picture of formation of disk galaxies is that density perturbations grow due to gravitational instability and end up forming virialized systems of dark matter and gas. The gas cools and collapses towards the center. The angular momentum of the gas is conserved during the collapse resulting in the formation of a centrifugally supported disk. The final surface density of disks can be determined once the angular momentum distribution of gas is known. We use a series of non radiative N-body/SPH simulations in a LCDM cosmology to study the angular momentum distribution of gas in Galactic Halos and find that that this distribution fails to reproduce the exponential structure of observed disks.

Next we discuss the phase space structure of dark matter halos. Density profiles of halos formed in simulations are known to follow a universal functional form. The origin of these profiles is still a mystery. In order to calculate the phase space densities we develop a method for multi-dimensional density estimation which is both very fast and accurate and present some sample applications.

2005 Jul 15 10:30 Institute conference


2005 Jul 08 10:30 Romano Corradi
(Isaac Newton Group, La Palma)

Planetary nebulae as luminosity tracers in (and outside) galaxies

Nowadays, planetary nebulae (PNe) are widely used to trace the luminosity of their parent stellar population, and have provided important result like the discovery of a significant amount of intracluster light in nearby galaxy clusters like Virgo and Coma.
I will discuss the potentiality and present uncertainties of this use of PNe as tracers of stellar light in galaxies. In particular, I will use data from galaxies of the Local Group, where the search for PNe is the most complete one, in order to test the predictions of new population synthesis models on the transformation factor between the PN population size and the total bolometric luminosity as a function of the galaxy type.

2005 Jun 23 15:00 Norbert Christlieb
(Hamburger Sternwarte)

Finding the most metal-poor stars with the Hamburg/ESO objective-prism survey

Metal-poor stars preserve in their atmospheres the chemical composition of the gas clouds from which they formed. The most metal-poor, and hence oldest stars of the Galaxy therefore allow to study the high-redshift Universe locally. They can provide information on the nature of the first generation of stars and the nucleosynthesis events associated with them.
I will given an overview of a dedicated effort to find metal-poor stars, which uses the digital database of the Hamburg/ESO objective-prism survey. I will also report on recent results from abundance analyses of metal-poor stars based on high-resolution spectroscopy obtained with the largest optical telescopes of the world.

2005 Jun 10 10:30 Vidar Aarum-Ulvås

Modelling the colour-brightness relation of spotted stars

2005 Jun 03 10:30 Lida Oskinova
(Univ. Potsdam)

X-ray emission from super star clusters

Super star clusters (SSC) have masses up to millions of solar masses and are the most extreme cases of star forming regions. Recent advantages in X-ray imaging and spectroscopy revealed that the X-ray emission differs drastically between SSCs of similar masses but different ages. I will describe the evolution of the X-ray emission from young massive star clusters based on a model that accounts for the stellar and the cluster wind emission. To model the evolution of the cluster wind, the mass and energy yields from a population synthesis are used as input to a hydrodynamic model. I will demonstrate that cluster X-ray output is tightly linked with stellar evolution. I will present the results of our analysis of Chandra and XMM-Newton observations of six massive star clusters located in the Large Magellanic Cloud. Our model reproduces the observed diffuse and point-source emission from these LMC clusters, as well as from the Galactic clusters Arches, Quintuplet and NGC 3603. The ability of current theories to predict the observed number of high mass X-ray binaries will be also discussed.

2005 May 26 10:30 Julio Navarro
(Univ. of Victoria)

The Structure of Cold Dark Matter Halos

I plan to discuss the results of recent simulations designed to further our understanding of the structure of Cold Dark Matter halos, and to contrast them with observation. I will summarize the latest numerical results as well as the status of some of the challenges posed by observations of strong gravitational lenses in galaxy clusters, as well as by the rotation curves of low surface brightness galaxies.

2005 May 20 14:00 Lise Christensen

The connection between galaxies and quasar absorption lines

Damped Lyman-alpha (DLA) lines seen in quasar spectra belong to neutral hydrogen clouds with high column densities and likely originate in galaxy disks. It is known that a large fraction of the neutral gas throughout the Universe is contained in DLAs, and hence they serve as reservoirs for formation of stars. Yet the galaxies in which the DLA clouds are residing remain to a large degree undetected. I will present first results of an integral field spectroscopic survey targeted towards detecting these DLA galaxies. The purpose is to understand the properties of the absorption selected proto-galaxies compared to galaxies observed in flux-limited samples, which have provided most of our current knowledge about the high redshift Universe.

2005 May 12 10:30 Institute conference


2005 Apr 29 10:30 Hans Ritter
(MPA Garching)

The Long-term Evolution of Low-mass X-ray Binaries

I shall review our current understanding (or lack thereof) of the long-term evolution of low-mass X-ray binaries (LMXBs). Similarities and differences between the evolution of LMXBs and that of cataclysmic binaries will be addressed. After a brief introduction to the principles of the evolution of semi-detached binaries, I shall concentrate on the main problems with which one is currently confronted when modelling the evolution of LMXBs. These are 1) systemic loss of orbital angular momentum via a process which is usually referred to as "magnetic braking", 2) common envelope evolution and other modes of angular momentum loss which arise as a direct consequence of mass transfer, 3) the evolutionary history and the evolutionary state of the donor star 4) the possible role of irradiation of the donor star by accretion luminosity from the compact star, 5) the role of giant accretion discs around the compact star in systems of very long orbital period (P > 20d). Finally, I shall discuss LMXBs as progenitors of millisecond pulsars.

2005 Apr 22 10:30 Georg Lamer

X-ray surveys with XMM-Newton

2005 Apr 15 10:30 Arif Babul
(Univ. of Victoria)

M31 Giant Southern Stream: The Quest for the Source

Mergers, disruption and assimilation of smaller scale structure into larger systems is a generic feature of hierarchical models. This assimilation process is expected to leave detritus in the halo of the larger systems that maintains its spatial and kinematic coherence for several billion years. And although identifying and qualifying such features is extremely challenging as it entails resolving and measuring properties of individual stars in the halos of the systems under study, their detailed study can provide important insights into the assembly of observed structure in the Universe, into the nature of the merging subunits themselves, and also into the dynamical properties of the host system. In this context, the discovery of the Sagittarius Stream in the Milky Way and the Giant Southern Stream in the Andromeda galaxies are important milestones. Here I will discuss our ongoing efforts to understand the origin of the M31 stream and identify its progenitor.

2005 Apr 08 10:30 Marco Spaans
(Univ. Groningen)

Chemistry in the Early Universe

The physical structure of gas clouds exposed to ultraviolet radiation, X-rays and cosmic rays is presented. The role of metallicity in the thermal and chemical balance of these clouds is discussed through the polytropic equation of state. Results are applied to starbursts, AGN and star formation in the high redshift universe and the possible variations in the resulting IMF of such environments are illustrated.

2005 Apr 01 10:30 Garik Israelian
(Inst. de Astrofísica de Canarias)

Chemical abundances in stars with exoplanets

Planet host stars are known to be metal rich when compared with otherwise "single" stars. This important observational fact may have far going implications and help us to develope consistent theories of planetary system formation. On the other hand, abundances of light elements Li and Be may allow to understand angular momentum evolution, flare activity and other interesting properties of stars with exoplanets. I shall review abundance trends of variour chemical elements in stars with planets and will make a critical discussion of the abundance trends in metal rich stars.

2005 Mar 18 10:30 Institute conference


2005 Mar 11 10:30 Svetlana Berdyugina
(ETH Zürich)

Large-scale non-axisymmetric magnetic fields and flip-flops on cool stars and the Sun

Rapidly rotating cool stars show a much higher level of activity over the Sun and may differ from the Sun in their dynamo mechanisms. For instance, they show prominent large-scale non-axisymmetric magnetic fields in the form of active longitudes. The dominant activity in such stars switches periodically from one active longitude to the opposite one exhibiting flip-flop cycles. A recent study of sunspot distribution has revealed similar behaviour on the Sun. It appears that there are more similarities between solar and stellar dynamos than was previously thought. I will give an overview of the properties of large-scale magnetic fields on cool active stars and compare them with those observed on the Sun.

2005 Mar 04 10:30 Wolfram Schmidt
(Univ. Würzburg)

An Astrophysicist's Tale on Subgrid Scale Modelling

The significance of subgrid scale models in fluid dynamical simulations is a controversial topic, particularly, in astrophysics. It is quite customary to apply the 'minimal solution', meaning that numerical dissipation is supposed to take care of everything on small, unresolved scales. An example for which the minimal solution does not suffice is turbulent combustion in type Ia supernovae. Based on my experience with adopting a so-called localised subgrid scale model from engineering, I will outline the difficulties and implications for this particular application. Moreover, I will try to motivate why the effort of implementing non-trivial subgrid scale models will pay off for virtually all kind of turbulent flows in astrophysics.

2005 Feb 25 10:30 Hakan Önel

Propagation of energetic electrons in the solar corona and interplanetary space

2005 Feb 18 10:30 Ewa Lokas
(Copernicus Center, Warsaw)

Dark matter distribution in the Draco dwarf

We study the distribution of dark matter in the Draco dwarf spheroidal galaxy by modelling the moments of the line-of-sight velocity distribution of stars obtained from new velocity data of Wilkinson et al. The luminosity distribution is approximated by a Sersic profile fitted to the data by Odenkirchen et al. We assume that the dark matter density profile is given by a formula with inner cusp and outer exponential cut-off recently proposed by Kazantzidis et al. as a result of simulations of tidal stripping of dwarfs by the potential of the Milky Way. Dark matter distribution is characterized by the total dark mass M_D and the cut-off radius r_b. The models have arbitrary velocity anisotropy parameter β assumed to be constant with radius. We estimate the three parameters by fitting both the velocity dispersion and kurtosis profiles which allows us to break the degeneracy between the mass distribution and velocity anisotropy. The results of the fitting procedure turn out to be very different depending on the stellar sample considered, that is on our choice of stars with discrepant velocities to be discarded as interlopers. For our most reliable sample the model parameters remain weakly constrained but the robust result is the preference for weakly tangential stellar orbits and high mass-to-light ratios. For this sample the best-fitting mass is 7 x 10^7 M_sun, much lower than recent estimates, while the mass-to-light ratio is M/L_V = 300 and almost constant with radius. If the binary fraction in the stellar population of Draco turns out to be significant the kurtosis estimate will decrease and the orbits inferred will be more tangential while the resulting mass estimate lower.

2005 Feb 11 10:30 Stefan Dreizler
(Universitätssternwarte Göttingen)

Stellar Astrophysics with MONET and SALT

In 2005, two telescopes with contributions from Göttingen Observatory will start operations. MONET (MOnitoring NEtwork of robotic Telescopes) consists of two 1.2m telescopes, one in Texas and one in South Africa whereas SALT (Southern African Large Telescope) is an 11m telescope, capable to explore the high time resolution domain in astrophysics. In my talk, I will summarize the status of the two telescope projects and an their impact on stellar astrophysics in Göttingen.

2005 Feb 04 10:30 Philipp Richter
(Univ. Bonn)

Searching for the Missing Baryons in the Warm-hot Intergalactic Medium

We discuss physical properties and the baryonic content of the Warm-hot Intergalactic Medium (WHIM) at low redshifts. Cosmological simulations predict that the WHIM contains a large fraction of the baryons at z=0 in the form of highly-ionized gas at temperatures between 10^5 and 10^7 K. Using high-resolution ultraviolet spectra obtained with the Space Telescope Imaging Spectrograph (STIS) and the Far Ultraviolet Spectroscopic Explorer (FUSE) we have studied the WHIM at low redshifts by searching for intervening O VI and thermally broadened Lyman alpha (BL) absorption toward a number of quasars and active galactic nuclei (AGNs). Our measurements imply cosmological mass densities of Omega_b(O VI) approx 0.0027/h_75 and Omega_b(BL) approx 0.0058/h_75. Our results suggest that the WHIM at low z contains more baryonic mass than stars and gas in galaxies.

2005 Jan 28 10:30 Monica Sanchez-Cuberes

Sunspot structure from spectropolarimetric measurements

2005 Jan 21 10:30 Institute conference


2005 Jan 14 10:30 Klaus Meisenheimer
(MPIA Heidelberg)

Resolving the Dusty Tori in AGN by Using the VLT as a 100m Telescope

Several lines of evidence argue for the "unified scheme" in which Seyfert I and Seyfert II galaxies are intrinsically similar objects, differing only in the angle under which we we observe them. Seyfert I's are observed nearly pole-on, allowing us a direct view onto the accretion disk, while this direct view seems blocked in Seyfert II's by a geometrically thick ring (so-called torus) of gas and dust in the equatorial plane. As various models for these tori produce very similar overall spectra, little progress can be made unless we actually "see" and resolve their dust emission. But even the largest single-dish telescopes are unable to do so. I will demonstrate how interferometric observations with the VLT - i.e. using the array of VLT telescope effectively as a 100m telescope - does not only deliver the required resolution in principle, but has in fact allowed us to resolve the torus emission of some nearby AGN like NGC 1068.

2004 Dec 17 10:30 Matthias Schreiber

Cataclysmic variables: Where do they come from?

2004 Dec 03 10:30 André Giesecke

Geodynamo alpha-effect derived from box simulations of rotating magnetoconvection

2004 Nov 26 10:30 Manfred Küker

Stellar dynamos and differential rotation

2004 Nov 19 10:30 Fabian Heitsch
(Universitätssternwarte München)

Turbulent ambipolar diffusion: numerical studies in 2D

Under ideal MHD conditions the magnetic field strength should be correlated with density in the interstellar medium (ISM). However, observations indicate that this correlation is weak. Ambipolar diffusion can decrease the flux-to-mass ratio in weakly ionized media; however, it is generally thought to be too slow to play a significant role in the ISM except in the densest molecular clouds. Turbulence is often invoked in astrophysical problems to increase transport rates above the (very slow) laminar values predicted by kinetic theory. We describe a series of numerical experiments addressing the problem of turbulent transport of magnetic fields in weakly ionized gases. We show, subject to various geometrical and physical restrictions, that turbulence in a weakly ionized medium rapidly diffuses the magnetic flux to mass ratio B/rho through the buildup of appreciable ion-neutral drifts on small scales. These results are applicable to the fieldstrength - density correlation in the ISM, as well as the merging of flux systems such as protostar and accretion disk fields or protostellar jets with ambient matter, and the vertical transport of galactic magnetic fields.

2004 Nov 17 11:00 Ingo Lehmann
(MPE Garching)

The cosmic evolution of AGN

2004 Nov 12 10:30 Institute conference

The Large Binocular Telescope

2004 Nov 05 10:30 Jochen Eislöffel
(TLS Tautenburg)

The formation and evolution of brown dwarfs

Several scenarios have been put forward recently for the formation of substellar objects, ranging from planet-like formation in a circumstellar disk to star-like formation through collapse of dense molecular cores. Here we present new observations of brown dwarfs and very low mass stars which show that at least some young brown dwarfs possess accretion disks, from which they are actively accreting matter. An intensive study of the light curves of very low-mass stars and brown dwarfs in open cluster with ages from 3 to 750 Myr allows us new insights into the rotational evolution of these objects, and has first implications for their magnetic fields and their dynamos and internal structure.

2004 Nov 01 10:30 Isabelle Baraffe
(AIP, Ecole Normale Supérior de Lyon)

All you ever wanted to know about "substellar objects"

2004 Oct 22 10:30 Robert Schmidt
(Univ. Potsdam)

Cosmology with Chandra observations of galaxy clusters

In this talk I present observations of a sample of the most X-ray luminous, dynamically relaxed galaxy clusters taken by NASA's Chandra X-ray observatory. These observations allow spatially resolved temperature measurements of the intergalactic medium and let us determine the mass of both the gas and the dark matter contained in the clusters. I will show how the Chandra data can be used to constrain the cosmic distance scale, to determine the matter density of the universe, and to study the effect of dark energy on the expansion of the universe.

2004 Sep 17 10:30 Yuexing Li
(American Museum of Natural History)

Star formation in galaxies

I will present high-resolution simulations of star formation in single disk galaxies and galaxy mergers. Our models of single galaxies quantitatively reproduce not only observed global and local Schmidt laws, but also observed star formation thresholds in disk galaxies, suggesting that the dominant physical mechanism determining the star formation rate is just the strength of gravitational instability. Galaxy mergers show significant starbursts, a lot of massive star clusters form in the tidal tails and bridges of the merging galaxies, they are identified as globular clusters. Our results demonstrate that gravitational instability and interaction are pivotal elements of cosmic structure formation and evolution.

2004 Sep 10 10:30 Nicolas Lodieu

Nearby brown dwarfs

In a first part, I will give an overview on brown dwarfs. I will give the definition, discuss the proposed formation mechanisms, and describe the different types of searches aimed at finding substellar objects in various environments. In a second part, I will present the results of a high proper motion survey in the Southern Sky conducted at the AIP by three of us (Ralf-Dieter Scholz, Mark McCaughrean, and myself) to uncover the closest and coolest neighbours to the Sun. I will highlight some of our discoveries, including two M dwarfs within 10 parsecs, an active late-M dwarf, and the closest binary brown dwarf, Epsilon Indi Ba,Bb.

2004 Sep 03 10:30 Alexander Warmuth

Flare-associated coronal shocks and waves

2004 Aug 27 10:30 Sergiy Silich
(INAOE, Mexico)

Star cluster winds

Here I discuss the expected appearance of the star cluster winds in the emission line and X-ray regimes. Special attention is payed to the modifications of the internal wind structure caused by the strong radiative cooling and to the wind appearance in the different ISM environments. It is shown that the dilution of the hard, intrinsic wind X-ray emission, by the soft component from the surrounding ISM bubble leads naturally to the two-temperature X-ray model which hardness is dependent on the surrounding gas density. The maximum X-ray luminosity may reach few times 10^39 erg s^-1.

2004 Jul 02 10:30 Anne-Katharina Jappsen

Gravoturbulent Fragmentation: Angular Momentum Evolution & Effects of a Non-isothermal Equation of State

Rotational properties of molecular cloud cores play an important role in star formation due to their influence on further collapse and on possible sub-fragmentation. Using hydrodynamic simulations we investigate the time evolution of the angular momentum of protostellar cores formed in various turbulent environments. We describe the relation between mass accretion and the growth of specific angular momentum and compare our results with observations of dense cloud cores.
A further fundamental problem in star formation is the identification of the processes that determine the initial mass function of stars (IMF). Most simulations of star forming clusters use an isothe rmal equation of state (EOS). However, this might be an oversimplification given the complex interplay between heating and cooling processes in molecular clouds. Theoretical predictions and observations suggest that the effective polytropic exponent gamma in the EOS changes with density.
In the second part of the talk we present the effects of a piecewise polytropic equation of state on the formation of stellar clusters in turbulent, self-gravitating molecular clouds. In our hydrodynamical simulations we increase the polytropic exponent gamma from 0.7 to 1.1 at some chosen density. This change in the EOS selects a characteristic mass scale which we relate to the peak of the observed IMF.

2004 Jun 25 10:30 Willy Kley
(Tübingen Univ.)

Distant Worlds: Observations and Theory of Extrasolar Planets

The number of detected extrasolar planets orbiting solar-type stars has risen to over 120. Their surprising orbital properties require a revision of the standard planet formation scenario. I will summarize the observational properties and present new results on the theoretical modeling of the formation and evolution of planetary systems.

2004 Jun 04 10:30 Stefan Schmeja

Star Formation from Gravoturbulent Fragmentation: Mass Accretion and Evolution of Protostars

Recently, both observations and numerical studies have suggested that star formation is controlled by supersonic turbulence rather than by magnetic fields. Supersonic turbulence is observed ubiquitously in molecular clouds, and while it provides support on a global scale, it can produce density enhancements that provoke local collapse. In this talk, protostellar mass accretion rates, lifetimes and evolutionary tracks resulting from numerical simulations of the fragmentation and collapse of turbulent, self-gravitating gas clouds will be discussed and compared to observations.

2004 May 25 10:30 Sun Kwok
(Inst. Astron. Astrophys., Academia Sinica, Taipei)

The Synthesis of Inorganic and Organic Compounds in the Circumstellar Environment

Recent observations by the Infrared Space Observatory (ISO) have found evidence of rapid synthesis of complex organic molecules in the late stages of stellar evolution. The chemical synthesis begins with the formation of acetylene, the first building block of benzene, in carbon stars. In a following proto-planetary nebulae stage, emission features corresponding to stretching and bending modes of aliphatic compounds are detected. When these objects evolve to become planetary nebulae, aromatic C-H and C-C stretching and bending modes become strong. These results show that complex carbonaceous compounds can be produced in a circumstellar environment over a period of only a few thousand years. Analysis of meteorites and interplanetary dust collected in the upper atmospheres have revealed the presence similar compounds, raising the possibility that the early solar system was chemically enriched by ejecta from evolved stars.

In this talk, we will discuss the formation of solid-state inorganic and organic compounds in stars, and speculate on the possible implications of these products on the formation of the solar system.

2004 May 14 10:30 Rolf-Peter Kudritzki
(IfA Honolulu)

Frontier science enabled by a giant segmented mirror telescope

2004 May 07 13:00 Carsten Kramer
(Univ. Köln)

Observations and modelling of photon-dominated regions - one central topic within the Cologne-Bonn Sonderforschungsbereich 494

The SFB494 on "The evolution of the interstellar medium: Terahertz spectroscopy in space and in the lab" encompasses astrophysical research, lab spectroscopy, and development of instrumentation. Two major aims are to prepare for SOFIA - the US/German Stratospheric Observatory for Infrared Astronomy and for the heterodyne instrument HIFI on-board the Herschel Space Observatory. I will present a short overview together with a few highlights. More information is available on .

In the second part of my talk, I will present recent results of large-scale observations of the interstellar molecular clouds complexes RCW106, Cygnus-X, and Perseus conducted by the KOSMA group. The aims are to characterize the density structure of the clouds, but also their temperatures and, more general, their energy balance. In detailed studies of the star forming regions S106, W3, and DR21, we have been modelling the emission of submillimeter and far-infrared lines of CO, CI, CII, OI etc. using models of photon-dominated regions.

2004 Apr 30 10:30 Jürgen Staude

Long-period eigenoscillations in the solar interior: solar and geophysical fingerprints?

2004 Apr 23 10:30 Christian Fendt
(AIP, Uni Potsdam)

Formation of Astrophysical Jets

2004 Apr 16 10:30 Klaus Beuermann

Evolutionary Catastrophes in the Earth's History

The talk provides an overview and a critical dicussion of the causes for the repeated mass extinctions in the Earth's history, confronting Luis Alvarz' meteorite impact hypothesis and the subsequent Hut et al. theory of disturbances of Oort's clud of comets as well as the more recent theory of violent volcanism with results from paleontological observations, the results from the Yucatan drilling project of the Princeton/Karlsruhe group, and the evidence from the analysis of impact structures. The debate has been raging for more than 20 years and still is one of the most controversial and heated of modern science.

2004 Apr 07 13:00 Henrik Beuther
(CfA, Cambridge, Mass.)

Early Science with the Submillimeter Array (SMA) on Mauna Kea/Hawaii

2004 Mar 26 10:30 Felix Mirabel

The AGN-Microquasar-GRB connection

I will review the progress made in the context of the analogy between AGN and microquasars that was proposed and developed in a series of articles published in Nature in the last decade. Since microquasars are fossils of gamma-ray-bursts sources of long duration, I propose to extend the analogy to these powerful cosmic explosions. If relativistic jets associated with the formation of black holes in GRB and accretion events in supermassive (AGN) and stellar black holes (microquasars) are due to a unique, universal magnetohydrodynamic mechanism, synergy between these three areas of research should lead to significative progress in black hole astrophysics.

2004 Mar 12 10:30 Ansgar Reiners
(Hamburger Sternwarte)

Stellar Differential Rotation - Results from Line Profile Analysis

Motivated by the solar differential rotation law and theory, astronomers try to detect deviations from solid body rotation in stars other than the Sun since the early 70's. Nowadays different approaches searching for differential rotation exist. Methods like Doppler imaging and the analysis of Ca emission trace stellar variations with time, and thus require large amounts of observational data - and observing time. Line profile analysis looks for the time-independent shape of absorption lines and requires only a single spectrum. The principles of this method will be outlined, and I present our results from analyzing some hundred spectra; in a few dozen stars signatures of strong differential rotation were found.

2004 Mar 05 10:30 Wolfgang Kalkofen
(KIS Freiburg)

Dynamics and Heating of Chromospheres

Our understanding of the heating of the solar and stellar chromospheres has achieved remarkable success in accounting for the gross properties of chromospheric radiation across the HR diagram; yet some important details, such as chromospheric temperature structure and the distribution of emission with height, indicate serious lacunae. The best and most detailed dynamical model of the quiet solar chromosphere explains the principle of the complex dynamical phenomenon of calcium bright points. But when the model is corrected for the effects of wave propagation in a stratified medium it fails to show the chromospheric temperature rise that is familiar from empirical models which have been constructed to fit time-average solar observations. This indicates serious flaws in our understanding of acoustic-wave phenomena in stellar chromospheres. The talk discusses what we have learned from the successes and, especially, from the failures of theoretical models.

2004 Feb 27 10:30 Natalia Dziourkevitch

The properties of MRI-driven turbulence in galaxies

2004 Feb 20 10:30 Stefan Rahmstorf

A cosmic influence on climate? Timing of Dansgaard-Oeschger events

2004 Feb 13 10:30 Harry Enke

Report on recent devlopments and issues within the Virtual Observatory

2004 Jan 23 10:30 Richard Sydora
(Univ. Alberta)

Progress in Coupling Magnetohydrodynamics to Particles with Stellar Physics Applications

2004 Jan 19 16:00 Michael Burton
(Univ. New South Wales, Sydney)

Astronomy in Antarctica

2004 Jan 16 10:30 Harald Kuntschner

Integral field spectroscopy of nearby galaxies with SAURON

I'm going to present the latest results from the SAURON survey of the kinematics and stellar populations of 72 nearby early-type galaxies. SAURON is an integral field unit mounted at the 4.2m William Herschel Telescope on La Palma. The survey is aimed at determining the intrinsic shape of the galaxies, their orbital structure, the age and metallicity of the stellar population(s) and the frequency of kinematically decoupled components.

2003 Dec 19 10:30 Heino Falcke
(Radio Obs. Westerbork, ASTRON, Dwingeloo)

LOFAR - The next generation radio telescope in the heart of Europe

2003 Dec 12 10:30 Stefano Bagnulo

Polarimetry with FORS1 at the ESO VLT

In the last few years we have witnessed a growing interest toward applications of polarimetric techniques in astronomical observations. Polarimetric modes are nowadays implemented at the instruments of the most modern telescopes, including the FORS1 instrument attached at the 8 m Unit 1 Antu of the ESO Very Large Telescope. Of special interest is the use of spectropolarimetry as a diagnostic tool for stellar magnetic fields. I will outline recent observational and modelling results, with special attention to the results of a survey of magnetic stars in Open Clusters carried out with FORS1 at the VLT.

2003 Dec 05 10:30 Thomas Granzer

Making astronomical observations robotic - A generic approach to robotic telescopes

2003 Nov 28 10:30 Karl Mannheim
(Uni Würzburg)

Searching for neutralino dark matter with gamma ray and neutrino telescopes

A new generation of gamma ray and high-energy neutrino telescopes will be used to search for the indirect signatures of neutralino dark matter. The lightest supersymmetric particle is perhaps the most plausible candidate for the dark matter, favored independently by the cosmological freeze-out condition and the nature of the hierarchy problem in the Standard Model of elementary particle physics. Success of the astroparticle physics approach to find signatures of the neutralino relies entirely on the control of the non-thermal astrophysical inventory in the 10 GeV - 1 TeV domain and experimental perfection. Deep observations will greatly improve our knowledge about the high-energy Universe and the origin of the diffuse, isotropic gamma ray background.

2003 Nov 14 10:30 Matthias Steinmetz

Unraveling the Formation History of the Galaxy with Computers and Telescopes

2003 Nov 07 10:30 Albert A. Zijlstra
(Astrophysics Group, UMIST, Manchester)

Stars: the end

Stars with low or intermediate masses, such as the Sun, experience a phase of catastrophic mass loss. This happens after the hydrogen and helium in the core becomes exhausted. The mass loss removes between 20% and 80% of its mass and effectively terminates the stellar evolution. The mass loss occurs while the star is a so-called Mira variable, where the visual brightness varies by more than factor of 100 with a period of around 1 year. In this talk I will address the dependence of the mass loss on the period and metallicity of the star.

2003 Sep 12 10:30 Christian Vocks

Suprathermal electrons in the solar corona and wind

2003 Jul 04 10:30 Matthias Hoeft

Reviving fossil radio plasma by galaxy mergers

2003 Jun 27 10:30 Günther Rüdiger

Magnetorotational instability in protoplanetary disks and the laboratory

2003 Jun 20 10:30 Stefanie Komossa
(MPE, Garching)

The X-ray search for supermassive black holes in nearby galaxies

The two X-ray observatories XMM-Newton and Chandra provided a wealth of new results on the environment of supermassive black holes in nearby (active) galaxies. The sharp imaging capabilities of Chandra and the high sensitivity of XMM-Newton also allowed a sentive search for X-ray weak or 'hidden' AGN at the centers of different types of galaxies, leading to some surprising results. In this overview, I will provide a summary of Chandra and XMM highlights on (active) galaxies. I will then concentrate on the recent discovery of a binary black hole in the nearby ultralumnious infrared galaxy NGC 6240, and will discuss the formation and evolution of such binary systems. I will conclude with the most recent results on an unusual phenomenon, first detected with ROSAT: giant-amplitude X-ray flares from the centers of nearby galaxies, interpreted as tidal disruptions of stars by supermassive black holes at the centers of these galaxies.

2003 Jun 06 10:30 Peter Ulmschneider
(Inst. für Theoret. Astrophysik, Univ. Heidelberg)

Progress in our understanding of stellar envelopes

Practically all stars are surrounded by very hot layers where the temperature can reach values almost as high as that in the stellar core. These layers are responsible for the observed radio, UV and X-ray emission and are essential for the mass-loss by stellar winds. I review the tedious quest for the understanding of the peculiar physics of these outer layers. In particular, I discuss the heating mechanisms and their relation to the magnetic field structure which are the cause of this surprising property of stars.

2003 May 23 10:30 Christoph Egbers
(TU Cottbus)

The GEOFLOW experiment on the International Space Station

2003 May 16 10:30 Peter Hauschildt

Model Atmospheres of M, L and T dwarfs

I will present selected new results of model atmosphere calculations with the PHOENIX code for very cool stellar and substellar objects and highlight some of the important (unknown) physics.

2003 May 09 10:30 Steven Kahler
(AIP, US Airforce)

Magnetic-field topology in the solar atmosphere and the interplanetary space

2003 Apr 25 10:30 Klaas S. de Boer
(Sternwarte, Universität Bonn)

Horizontal Branch Stars and Galactic Kinematics

Searches at high galactic latitudes have uncovered many stars of horizontal-branch (HB) type (the sdO, sdB, HBB, HBA, RR Lyr stars). These stars are relatively easy to classify. In a programme including spectroscopy, photometry, and astrometry we were able to derive distances, radial velocities, and proper motions. Using a mass model of the Milky Way, one then can calculate the galactic orbits. A considerable fraction of the HB stars has disk-like kinematics, others are rather halo-like in their motion. The orbits allowed to uncover interesting aspects of the spatial distribution of these stars.

2003 Apr 11 10:30 Bodo L. Ziegler
(Universtitätssternwarte Göttingen)

Kinematic Evolution of Galaxies

With the availability of big telescopes and powerful instruments it is now feasible to study galaxy evolution quantitatively out to high redshifts. We exploit these possibilities by measuring the internal kinematics of galaxies out to redshift of 1. With the aid of scaling relations like the Tully-Fisher relation of disk galaxies we robustly quantify not only the luminosity but in particular the mass evolution of galaxies. This enables us to give very tight constraints on galaxy formation models that give clear predictions on the mass evolution of Dark Matter halos. We explore the kinematics not only for field galaxies but also galaxies in clusters where additional environmental effects influence the evolution of a galaxy.

2003 Mar 28 10:30 Andreas Eckart
(Universität zu Köln)

The massive Black Hole associated with SgrA*

Most recent measurements from the radio to the X-ray domain provide unprecedented convincing evidence for the presence of a massive black hole at the center of our Milky Way. The results of stellar orbital measurements from the NAOS/CONICA VLT adaptive optics measurements as well as results from the recent simultaneous X-ray, infrared, radio monitoring campaign on Sagittarius A* will be presented.

2003 Mar 21 11:00 Klaus G. Strassmeier

PEPSI@LBT: optical spectra for you

2003 Mar 07 11:00 Heidi Korhonen

Star Spots on FK Com: Flip-Flops and Active Longitudes

2003 Feb 28 11:00 Achim Feldmeier
(Institut fr Astrophysik, Universitt Potsdam)

Tides on Earth and in Galaxies

The talk gives an introduction into old and new tidal phenomena, with an emphasis on tides as shallow water waves. The following issues are addressed: why is, for tides on an ideal Earth without land, the water level lowest under the Moon, and not highest? Why does Io show dramatic tidal effects like volcano eruptions, instead of orbiting on a perfect circle around Jupiter? Are grand design spiral galaxies, contrary to the Lin-Shu hypothesis, transient phenomena, excited by tidal forces due to a close companion?

2003 Jan 31 11:00 Dominik J. Bomans
(Astronomisches Institut der Ruhr-Universitaet Bochum)

Low Surface Brightness Galaxies in Deep Fields

The inventory of local galaxies is still quite incomplete, to large extent due to the difficulties of detecting low surface brightness (LSB) galaxies. This leads to a critical shortcoming of our understanding of galaxy formation and evolution. We do not know why and how often a protogalaxy developes into a low surface brightness galaxy instead of a "normal" high surface brightness spiral or irregular galaxy. With the Sloan Digital Sky survey significant progress can be expected for the characterisation of the galaxy content of the local universe, but the explored parameter space will be still far from complete. Using deep CCD mosaic cameras we can probe very small scale length and very low central surface brightness galaxies beyond the limits of previous LSB galaxy searches. I will present some results from our multi-color surveys, demonstrate problems (and solutions) for selecting local (and relatively low redshift) LSB galaxies against a background of high redshift field galaxies and show some new results on the space density and evolution of LSB galaxies.

2003 Jan 24 11:00 Marc Verheyen

The Distribution of Mass in Spiral Galaxies

2003 Jan 17 11:00 Pavel Kroupa
(Institut fr Theoretische Physik und Astrophysik, Universitt Kiel)

Star clusters, the fundamental building blocks of galaxies

The current consensus is that stars form in a range of embedded star clusters. Dense, rich clusters dissolve binaries and harbour massive stars which explode as Type II supernovae. They are long-lived allowing white-dwarf binaries to harden thus enhancing the rate of type Ia supernovae. Feedback from its stars destroys the gaseous envelope of a young cluster such that on expulsion of the gas most of the cluster becomes unbound. The expanding stellar population leaves imprints in the stellar phase-space distribution function which defines the morphological appearance of galaxies. The shape and extend of galaxies, their stellar binary fraction and chemical enrichment history are thus intrinsically linked to the history of star formation in clusters. Specifically, the mass function of star clusters and its variation with the star formation rate are the fundamental functions driving the evolution of stellar populations. The star formation rate is modulated through galactic perturbations and mergers, as well as intrinsic dynamical instabilities of galaxies. This talk will attempt to give an overview of this topic, with a focuss on determinations of the cluster mass function.

2003 Jan 10 11:00 Knud Jahnke

Stellar Populations of QSO Host Galaxies

2002 Dec 20 11:00 Sepehr Arbabi-Bidgoli

Cosmology with Voids

2002 Dec 19 16:00 Wolfgang J. Duschl
(Institut für Theoretische Astrophysik, Universität Heidelberg)

The formation and feeding of super-massive Black Holes

2002 Dec 06 11:00 Janusz Gil
(AIP, Univ. of Zielona Góra)

A Mystery of Pulsar Radio Emission

2002 Nov 28 16:00 Carlos Frenk
(Institute of Computational Cosmology, Physics Department, University of Durham)

The Cold Dark Matter Paradigm

2002 Nov 22 11:00 Michael I. Andersen

Gamma-ray Bursts: Afterglows and Host Galaxies

2002 Nov 14 16:00 Simon Jeffery
(Armagh Observatory, St. Andrews University)

The progeny of binary white dwarf mergers; extreme helium stars, R CrB stars and subdwarf B stars

2002 Nov 08 11:00 Russell Cannon

Part III: Two Thousand Carbon Stars in the Magellanic Clouds

2002 Oct 29 16:00 Russell Cannon

Part II: The 2dF Instrument and the Galaxy Redshift Survey

2002 Oct 18 11:00 Walter Dehnen

The Tidal Tail of the Globular Cluster Pal 5

2002 Oct 17 16:00 Rudolf Dvorak
(University of Vienna)

Dynamics of Extrasolar Planetary Systems

2002 Oct 11 11:00 Russell Cannon

Part I: The Chemical Composition of Stars in Globular Clusters: Clues to Their History and Star Formation Processes

2002 Aug 30 11:00 Andreas Staude

The Bright and Dark Sides of Polars

2002 Jul 26 11:00 Andreas Faltenbacher

Merging of Galaxy Clusters

2002 Jul 17 16:00 Rolf P. Kudritzki
(University of Hawaii)

Extragalactic Stellar Astronomy

2002 Jul 03 16:00 Yehuda Hoffman
(Racah Institute of Physics, Hebrew University Jerusalem)

The Structure of Dark Matter Halos

2002 Jun 28 11:00 Rainer Arlt

Stars, Disks, Galactic Nuclei: the Magneto-Rotational Instability

2002 Jun 14 11:00 Yvonne Simis

Dust Forming Stellar Winds

2002 May 31 11:00 Ralf Klessen

Star Formation in Molecular Clouds

2002 May 22 16:00 Ken Freeman
(Mount Stromlo Observatory)

The Galaxy: Signatures of its Formation

2002 May 17 11:00 Matthias Steinmetz

The Fine Structure of Disk Galaxies

2002 Apr 10 16:00 Matthias Schreiber
(Universitätssternwarte, Göttingen)

Constraints on the Disk Instability Model from Observations of Dwarf Novae

2002 Apr 05 11:00 Hans-Erich Fröhlich

EK Draconis - the Most Active Solar Twin

2002 Apr 02 16:00 Yusef Sobouti
(Center for Theoretical Physics and Mathematics, Teheran)

The Toroidal Modes of Rotating Fluid Masses

2002 Mar 08 11:00 Ulrich Geppert

Neutron Stars

2002 Feb 28 16:00 Wolfgang Voges
(MPI f. extraterrestr. Physik, Garching)

Virtual Observatory

2002 Jan 30 16:00 Ralf-Jürgen Dettmar
(Ruhr-Universität Bochum)

Structure and evolution of the stellar components in disk galaxies

2002 Jan 11 11:00 Horst Balthasar

Observations of Sunspots with the Tenerife Infrared Polarimeter

2001 Dec 19 16:00 Christian Spiering
(Institut für Hochenergiephysik Zeuthen)

AMANDA -- High Energy Neutrino Astronomy at the South Pole

2001 Dec 16 11:00 Harold W. Yorke
(Jet Propulsion Laboratory, Pasadena)

Beyond SIRTF, SOFIA, and Herschel: New Concepts for Far Infrared Telescopes

The 40-450 micron regime offers a unique window to the Universe. After the successful conclusion of the ISO mission, the upcoming FIR facilities SIRTF, SOFIA, and Herschel will provide a wealth of information on early and late phases of stellar evolution, galaxy formation and evolution, and the evolution of cosmic dust from its production in Red Giants to the formation of planetesimals. Potentially even greater scientific yield is possible with higher sensitivity and higher spatial resolution. A new generation of FIR space observatories beyond SIRTF and Herschel will complement in a unique manner telescopes operating in other wavelength regimes, such as HST, NGST, and ALMA. Large, filled aperture telescopes and imaging interferometers operating in this wavelength range can be built and deployed in space within 8 - 15 years. Given the successful conclusion of the upcoming SIRTF and Herschel missions, an operating SOFIA facility as well as NGST and ALMA, what unique and compelling science will be enabled by these new FIR/Submm observatories? What technological developments are necessary to prepare for their construction?

2001 Dec 07 11:00 Jesper Storm

Cepheids and the Distance Scale

2001 Nov 23 11:00 Detlef Elstner

The Galactic Dynamo - Success and limitations of current models

2001 Nov 09 11:00 Stefan Gottlöber

Evolution of Galaxies in Different Environments

2001 Oct 21 11:00 Martin M. Roth

3D Spectroscopy with PMAS

2001 Sep 28 11:00 Gottfried Mann

Wave Phenomena on the Dynamic Sun

2001 Sep 14 11:00 Matthias Hoeft

Energy Transfer from Larger to Smaller Scales: a Tracer for Star Formation in Cosmological Simulations?

2001 Jun 01 11:00 Günther Rüdiger

Two Types of Stellar Dynamos

2001 May 18 11:00 Ralf-Dieter Scholz

Search for the missing stars in the Solar neighbourhood

2001 May 04 11:00 Jürgen Staude

GREGOR: A 1.5-m Telescope for Solar Research

2001 Apr 20 11:00 Volker Müller

The Supercluster-Void-Network

2001 Apr 06 11:00 Thomas Granzer

Can We Successfully Apply a Solar Thin-Flux-Tube Model to Active Stars?

2001 Mar 23 11:00 Günther Hasinger

The History of Black Holes

2001 Mar 09 11:00 Matthias Steffen

RHD Simulations of Stellar Convection

2001 Feb 23 11:00 Axel Schwope

Magnetic Fields in Polars

2001 Feb 09 11:00 T. Carroll, A. Kelz, K. Muglach, M. Weber

Polarized Radiation and Polarimetry

2001 Jan 26 11:00 Hans Zinnecker

Stellar evolution before the main sequence

2001 Jan 12 11:00 Klaus G. Strassmeier

STELLA - A New Telescope for the Teide Observatory

Forthcoming colloquia