Kolloquien und Seminare (2001-2005)


2001 · 2002 · 2003 · 2004 · 2005


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

Exploring the transient universe with Pan-STARRS

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

The COSMOS and zCOSMOS surveys

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

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

Stellar Hydrodynamics and Nuclear Astrophysics

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

2005 Nov 25 10:30 Andrea Cattaneo

Self-regulated black hole growth in a quiescent galaxy

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

Diagnostics of Sunspots and Active Regions by Local Helioseismology

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

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

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

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

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

Helioseismology of the Global Structure and Dynamics of the Sun

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

2005 Nov 11 10:30 Institute conference


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

Wempe Prize colloquium

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

Sunquakes and Helioseismology

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

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

How to avoid dwarf galaxy formation

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

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

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

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

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

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

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

2005 Jul 22 10:30 Sanjib Sharma

Angular Momentum Distribution and Phase Space Structure of Galactic Halos

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

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

2005 Jul 15 10:30 Institute conference


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

Planetary nebulae as luminosity tracers in (and outside) galaxies

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

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

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

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

2005 Jun 10 10:30 Vidar Aarum-Ulvås

Modelling the colour-brightness relation of spotted stars

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

X-ray emission from super star clusters

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

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

The Structure of Cold Dark Matter Halos

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

2005 May 20 14:00 Lise Christensen

The connection between galaxies and quasar absorption lines

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

2005 May 12 10:30 Institute conference


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

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

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

2005 Apr 22 10:30 Georg Lamer

X-ray surveys with XMM-Newton

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

M31 Giant Southern Stream: The Quest for the Source

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

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

Chemistry in the Early Universe

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

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

Chemical abundances in stars with exoplanets

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

2005 Mar 18 10:30 Institute conference


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

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

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

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

An Astrophysicist's Tale on Subgrid Scale Modelling

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

2005 Feb 25 10:30 Hakan Önel

Propagation of energetic electrons in the solar corona and interplanetary space

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

Dark matter distribution in the Draco dwarf

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

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

Stellar Astrophysics with MONET and SALT

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

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

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

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

2005 Jan 28 10:30 Monica Sanchez-Cuberes

Sunspot structure from spectropolarimetric measurements

2005 Jan 21 10:30 Institute conference


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

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

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

2004 Dec 17 10:30 Matthias Schreiber

Cataclysmic variables: Where do they come from?

2004 Dec 03 10:30 André Giesecke

Geodynamo alpha-effect derived from box simulations of rotating magnetoconvection

2004 Nov 26 10:30 Manfred Küker

Stellar dynamos and differential rotation

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

Turbulent ambipolar diffusion: numerical studies in 2D

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

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

The cosmic evolution of AGN

2004 Nov 12 10:30 Institute conference

The Large Binocular Telescope

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

The formation and evolution of brown dwarfs

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

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

All you ever wanted to know about "substellar objects"

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

Cosmology with Chandra observations of galaxy clusters

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

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

Star formation in galaxies

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

2004 Sep 10 10:30 Nicolas Lodieu

Nearby brown dwarfs

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

2004 Sep 03 10:30 Alexander Warmuth

Flare-associated coronal shocks and waves

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

Star cluster winds

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

2004 Jul 02 10:30 Anne-Katharina Jappsen

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

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

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

Distant Worlds: Observations and Theory of Extrasolar Planets

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

2004 Jun 04 10:30 Stefan Schmeja

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

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

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

The Synthesis of Inorganic and Organic Compounds in the Circumstellar Environment

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

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

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

Frontier science enabled by a giant segmented mirror telescope

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

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

The SFB494 on "The evolution of the interstellar medium: Terahertz spectroscopy in space and in the lab" encompasses astrophysical research, lab spectroscopy, and development of instrumentation. Two major aims are to prepare for SOFIA - the US/German Stratospheric Observatory for Infrared Astronomy and for the heterodyne instrument HIFI on-board the Herschel Space Observatory. I will present a short overview together with a few highlights. More information is available on http://www.ph1.uni-koeln.de/workgroups/sfb/ .

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

2004 Apr 30 10:30 Jürgen Staude

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

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

Formation of Astrophysical Jets

2004 Apr 16 10:30 Klaus Beuermann

Evolutionary Catastrophes in the Earth's History

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

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

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

2004 Mar 26 10:30 Felix Mirabel

The AGN-Microquasar-GRB connection

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

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

Stellar Differential Rotation - Results from Line Profile Analysis

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

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

Dynamics and Heating of Chromospheres

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

2004 Feb 27 10:30 Natalia Dziourkevitch

The properties of MRI-driven turbulence in galaxies

2004 Feb 20 10:30 Stefan Rahmstorf

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

2004 Feb 13 10:30 Harry Enke

Report on recent devlopments and issues within the Virtual Observatory

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

Progress in Coupling Magnetohydrodynamics to Particles with Stellar Physics Applications

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

Astronomy in Antarctica

2004 Jan 16 10:30 Harald Kuntschner

Integral field spectroscopy of nearby galaxies with SAURON

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

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

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

2003 Dec 12 10:30 Stefano Bagnulo

Polarimetry with FORS1 at the ESO VLT

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

2003 Dec 05 10:30 Thomas Granzer

Making astronomical observations robotic - A generic approach to robotic telescopes

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

Searching for neutralino dark matter with gamma ray and neutrino telescopes

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

2003 Nov 14 10:30 Matthias Steinmetz

Unraveling the Formation History of the Galaxy with Computers and Telescopes

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

Stars: the end

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

2003 Sep 12 10:30 Christian Vocks

Suprathermal electrons in the solar corona and wind

2003 Jul 04 10:30 Matthias Hoeft

Reviving fossil radio plasma by galaxy mergers

2003 Jun 27 10:30 Günther Rüdiger

Magnetorotational instability in protoplanetary disks and the laboratory

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

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

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

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

Progress in our understanding of stellar envelopes

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

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

The GEOFLOW experiment on the International Space Station

2003 May 16 10:30 Peter Hauschildt

Model Atmospheres of M, L and T dwarfs

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

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

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

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

Horizontal Branch Stars and Galactic Kinematics

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

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

Kinematic Evolution of Galaxies

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

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

The massive Black Hole associated with SgrA*

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

2003 Mar 21 11:00 Klaus G. Strassmeier

PEPSI@LBT: optical spectra for you

2003 Mar 07 11:00 Heidi Korhonen

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

2003 Feb 28 11:00 Achim Feldmeier
(Institut f�r Astrophysik, Universit�t Potsdam)

Tides on Earth and in Galaxies

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

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

Low Surface Brightness Galaxies in Deep Fields

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

2003 Jan 24 11:00 Marc Verheyen

The Distribution of Mass in Spiral Galaxies

2003 Jan 17 11:00 Pavel Kroupa
(Institut f�r Theoretische Physik und Astrophysik, Universit�t Kiel)

Star clusters, the fundamental building blocks of galaxies

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

2003 Jan 10 11:00 Knud Jahnke

Stellar Populations of QSO Host Galaxies

2002 Dec 20 11:00 Sepehr Arbabi-Bidgoli

Cosmology with Voids

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

The formation and feeding of super-massive Black Holes

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

A Mystery of Pulsar Radio Emission

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

The Cold Dark Matter Paradigm

2002 Nov 22 11:00 Michael I. Andersen

Gamma-ray Bursts: Afterglows and Host Galaxies

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

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

2002 Nov 08 11:00 Russell Cannon

Part III: Two Thousand Carbon Stars in the Magellanic Clouds

2002 Oct 29 16:00 Russell Cannon

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

2002 Oct 18 11:00 Walter Dehnen

The Tidal Tail of the Globular Cluster Pal 5

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

Dynamics of Extrasolar Planetary Systems

2002 Oct 11 11:00 Russell Cannon

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

2002 Aug 30 11:00 Andreas Staude

The Bright and Dark Sides of Polars

2002 Jul 26 11:00 Andreas Faltenbacher

Merging of Galaxy Clusters

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

Extragalactic Stellar Astronomy

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

The Structure of Dark Matter Halos

2002 Jun 28 11:00 Rainer Arlt

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

2002 Jun 14 11:00 Yvonne Simis

Dust Forming Stellar Winds

2002 May 31 11:00 Ralf Klessen

Star Formation in Molecular Clouds

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

The Galaxy: Signatures of its Formation

2002 May 17 11:00 Matthias Steinmetz

The Fine Structure of Disk Galaxies

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

Constraints on the Disk Instability Model from Observations of Dwarf Novae

2002 Apr 05 11:00 Hans-Erich Fröhlich

EK Draconis - the Most Active Solar Twin

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

The Toroidal Modes of Rotating Fluid Masses

2002 Mar 08 11:00 Ulrich Geppert

Neutron Stars

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

Virtual Observatory

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

Structure and evolution of the stellar components in disk galaxies

2002 Jan 11 11:00 Horst Balthasar

Observations of Sunspots with the Tenerife Infrared Polarimeter

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

AMANDA -- High Energy Neutrino Astronomy at the South Pole

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

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

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

2001 Dec 07 11:00 Jesper Storm

Cepheids and the Distance Scale

2001 Nov 23 11:00 Detlef Elstner

The Galactic Dynamo - Success and limitations of current models

2001 Nov 09 11:00 Stefan Gottlöber

Evolution of Galaxies in Different Environments

2001 Oct 21 11:00 Martin M. Roth

3D Spectroscopy with PMAS

2001 Sep 28 11:00 Gottfried Mann

Wave Phenomena on the Dynamic Sun

2001 Sep 14 11:00 Matthias Hoeft

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

2001 Jun 01 11:00 Günther Rüdiger

Two Types of Stellar Dynamos

2001 May 18 11:00 Ralf-Dieter Scholz

Search for the missing stars in the Solar neighbourhood

2001 May 04 11:00 Jürgen Staude

GREGOR: A 1.5-m Telescope for Solar Research

2001 Apr 20 11:00 Volker Müller

The Supercluster-Void-Network

2001 Apr 06 11:00 Thomas Granzer

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

2001 Mar 23 11:00 Günther Hasinger

The History of Black Holes

2001 Mar 09 11:00 Matthias Steffen

RHD Simulations of Stellar Convection

2001 Feb 23 11:00 Axel Schwope

Magnetic Fields in Polars

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

Polarized Radiation and Polarimetry

2001 Jan 26 11:00 Hans Zinnecker

Stellar evolution before the main sequence

2001 Jan 12 11:00 Klaus G. Strassmeier

STELLA - A New Telescope for the Teide Observatory