# Colloquia and Special Seminars (2006-2010)

2006 · 2007 · 2008 · 2009 · 2010

DateTimeTalk internal - external
2010
2010 Dec 17 10:30 Adrian Partl
(AIP)

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
(AIP)

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
(ETH)

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
(MPIA)

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
(AIP)

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
(MPIA)

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
(AIP)

tba.

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
(AIP)

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
(AIP)

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
(AIP)

The formation of disc galaxies in a cosmological context

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

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
(AIP)

tba.

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
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
(AIP)

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)

tba.

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
(AIP)

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
(AIP)

All-institute meeting

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

2009 Sep 04 10:30 Wolfgang Gieren

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
(AIP)

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
(MPA)

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
(AIP)

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

[Programme]

2009 May 25 14:00 Special Colloquium
(AIP)

Wempe Award Ceremony for Dr. Matthias Rempel

2009 May 08 10:30 Igor di Varano
(AIP)

ICE-T: two eyes pointing at Dome C

2009 Apr 24 10:30 Stefan Gottlöber
(AIP)

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
(AIP)

The satellites of the Milky Way

2009 Feb 27 10:30 Jose Manuel Ramirez Velasquez
(AIP)

tba.

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
(AIP)

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
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
(AIP)

Wempe Award Ceremony

14:00
Opening, laudatio, and ceremony
15:30
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
(AIP)

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
(AIP)

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
(AIP)

Structure of Dark Matter Haloes in Scale-Free Cosmologies

2008 Oct 17 10:30 Leonid Kitchatinov
(AIP)

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
(AIP)

10000 MHD-Tage in Potsdam

14:00
Klaus Strassmeier - Bereichsdirektor des AIP für Kosmische Magnetfelder
14:20
Beiträge von Frank Stefani, Marcus Gellert, Horst Balthasar, Nobert Seehafer, Manfred Schüssler
15:40
Pause, anschließend
Beiträge von Manfred Küker, Hans-Erich Fröhlich, Detlef Elstner, Oliver Gressel
17:00
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
(AIP)

tba.

2008 Apr 25 10:30 Isabelle Gavignaud
(AIP)

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
(AIP)

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
(AIP)

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
(AIP)

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
(AIP)

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
(AIP)

Reconstruction of magnetic fields in the solar corona

2008 Jan 11 10:30 Spyridon Kitsionas
(AIP)

Interstellar turbulence and star/planet formation

2007
2007 Dec 14 10:30 Thorsten Ratzka
(AIP)

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
(AIP)

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
(AIP)

Science with STELLA

2007 Nov 23 10:30 Ralf-Dieter Scholz
(AIP)

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
(AIP)

Ignasi Ribas

2007 Nov 02 10:30 Oliver Gressel
(AIP)

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
(AIP)

Zentrum fuer Innovationskompetenz: innoFSPEC

2007 Oct 19 10:30 Horst Balthasar
(AIP)

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
(AIP)

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
(AIP)

Zum 80. Geburtstag von Prof. Fritz Krause

2007 Jun 01 10:30 Michael I. Andersen
(AIP)

Gamma-ray bursts in the SWIFT era

2007 May 25 10:30 Simon Glover
(AIP)

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
(AIP)

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
(AIP)

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
(AIP)

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
(AIP)

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
(AIP)

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
(AIP)

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
(AIP)

Galactic Dynamos

2007 Jan 08 10:30 Institute conference
(AIP)

Evaluierung 2007

2006
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
(AIP)

PROMISE

2006 Dec 01 10:30 Henry Aurass
(AIP)

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

2006 Nov 24 10:30 Heidi Korhonen
(AIP)

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
(AIP)

Ultra-Luminous Infrared Galaxies

2006 Oct 20 10:30 Michael Weber
(AIP)

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
(AIP)

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
(AIP)

Dark energy

2006 Sep 08 10:00 Festkolloquium Wempe Award
(AIP)

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
(AIP)

Bayesian period search

2006 Jun 30 10:30 Christian Vocks
(AIP)

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

2006 Jun 23 10:30 Gwendolyn Meeus
(AIP)

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
(AIP)

ICE-T

2006 May 24 09:00 Workshop
(AIP)

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
(AIP)

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
(AIP)

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
(AIP)

Studying young stars with the VLT Interferometer

2006 Apr 21 10:30 Rainer Arlt
(AIP)

How magnetic is the solar tachocline?

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

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

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
(AIP)

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
(AIP)

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
(AIP)

LOFAR

2006 Jan 13 10:30 Ralf Klessen
(AIP)

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
(AIP)

The physics of solar eruptions