Special Seminars: 2007
DateTalk TitleSpeaker
Feb 6, 2007CaII absorption line systems: dust, metals and star formation in the outskirts of galaxiesVivienne Wild, Max Planck Institut für Astrophysik
Feb 27, 2007A SIMPLE way to identify MgII absorbersNicholas Bouche, Max-Planck-Institut Für extraterrestrische Physik
May 15, 2007Unsolved Problems of Magnetoplasma TurbulenceRoald Sagdeev, University of Maryland
Jun 8, 2007Spitzer observations of star- and planet-forming regions: From ice cold to steaming hotEwine van Dishoeck, Leiden Observatory, The Netherlands
Jun 8, 2007Deconstructing Nearby GalaxiesTim de Zeeuw, Leiden Observatory
Jun 26, 2007Extrasolar Planets as a Blemish in Einstein's TelescopeDavid Bennett, University of Notre Dame
Aug 10, 2007The burst mode of accretion in the early evolutionary phase of low-mass protostarsEduard Vorobyov, University of Western Ontario
Oct 18, 2007Using RR Lyrae Variable Stars to Probe the Kinematic Signature of the Sagittarius StreamRon Wilhelm, Texas Tech

CaII absorption line systems: dust, metals and star formation in the outskirts of galaxies
Feb 6, 2007 | LASR | 1:30 AM
Vivienne Wild, Max Planck Institut für Astrophysik

The true nature of strong quasar absorption line systems, galaxies detected through the absorption of background QSO light by interstellar/halo gas, remains unclear even after many years of investigation. I will discuss the properties of an unusual class of absorption system selected through interstellar CaII (H&K) lines from the SDSS QSO catalogue. Results include their unusually high dust contents and dust-to-metals ratios, associated star formation from detected OII emission, and recent K-band imaging of the old stellar populations at z~1.

A SIMPLE way to identify MgII absorbers
Feb 27, 2007 | AAC 123 | 12:00 PM
Nicholas Bouche, Max-Planck-Institut Für extraterrestrische Physik

MgII seen in QSO spectra traces cold gas with physical properties similar to those of the cold gas in superwinds. It is therefore expected that there would be an overlap between starburst galaxies and MgII-selected galaxies. The problem -up to now- is that galaxies selected in absorption are usually hard to detect in emission, as previous attempts often failed.

Based on SDSS, we found that the halo mass of absorbers is anti-correlated with equivalent width. This implies that the clouds traced by MgII are not virialized in the halos of the host-galaxy.

These SDSS results led us to design a SIMPLE (SINFONI MgII program for line emitters) way to identify the host-galaxy at z=1 and z=2. The technique successfully detects a starburst in 75% of the cases, and opens the possibility to study the kinematics of superwinds out to z=2 and up to 50kpc from the host galaxy.

Unsolved Problems of Magnetoplasma Turbulence
May 15, 2007 | LASR | 2:00 PM
Roald Sagdeev, University of Maryland

Many of Space- and Astro- Physics related problems force to go beyond classical Kolmogoroff Turbulence. The whole class of "Dispersive Turbulence" in Hamiltonian Media required the "Weak Turbulence" approach, introducing ensemble of quasiparticles=waves. Nonlinear evolution of spectra often lead to self-generation of large scale flows representing purely classical analog of Bose-Einstein condensation.

Among specific applications: "MHD"-Turbulence associated with Galactic Cosmic Ray Shocks, Solar Wind induced non-linear structures.

Spitzer observations of star- and planet-forming regions: From ice cold to steaming hot
Jun 8, 2007 | RI 480 | 9:00 AM
Ewine van Dishoeck, Leiden Observatory, The Netherlands

The earliest stages of star- and planet formation are obscured by tens to hundreds of magnitudes of extinction. Observations of the gas and dust at long wavelengths often provide the only way to obtain information on the physical and chemical processes that occur deep inside these regions. In this talk, an overview of Spitzer spectroscopic observations of ices, silicates, PAHs and hot gases will be given. Spitzer has opened up the possibility to obtain high quality mid-infrared spectra for large numbers of low-mass protostars and disks around solar-mass pre-main sequence stars for the first time. The results will be placed in the context of other space- and ground-based data and analyzed using models of protostellar envelopes and (flaring) disks. The diagnostic values of the various lines and bands will be emphasized, and the importance of laboratory data to interpret them will be illustrated. The prospects for future facilities, in particular the Herschel Space Observatory, the James Webb Space Telescope and the Atacama Large Millimeter Array, will be discussed.

Deconstructing Nearby Galaxies
Jun 8, 2007 | RI 480 | 10:30 AM
Tim de Zeeuw, Leiden Observatory

Much world-wide effort is devoted to the study of the formation and evolution of galaxies, ranging from observations of the most distant objects in the early Universe to detailed analysis of the motions of individual stars in the Milky Way, combined with theoretical work and numerical simulations. Recent developments in optical instrumentation make it possible to measure the motions and physical properties of stellar populations in nearby galaxies, and to determine the properties of the supermassive black holes in their centres. A representative survey of nearby early-type galaxies and spiral bulges with SAURON, a panoramic integral-field spectrograph custom-built for the UK/NL/E 4.2m William Herschel Telescope on La Palma, reveal a fascinating diversity of properties. The observed stellar and gaseous kinematics and the line-strength distributions provide the intrinsic shape of the galaxies, their orbital structure, the mass-to-light ratio as a function of radius, the frequency of kinematically decoupled cores, the masses of nuclear black holes, and the relation between orbital structure and the age and metallicity of the stellar populations. This 'fossil record' provides key insight into the galaxy formation process. The talk will summarize the main results of the SAURON survey, and briefly consider the next steps, including the possibilities provided by instrumentation on 8m class telescopes.

Extrasolar Planets as a Blemish in Einstein's Telescope
Jun 26, 2007 | AAC 123 | 12:00 PM
David Bennett, University of Notre Dame


The burst mode of accretion in the early evolutionary phase of low-mass protostars
Aug 10, 2007 | RI 180 | 1:00 PM
Eduard Vorobyov, University of Western Ontario

We present new numerical simulations in the thin-disk approximation which characterize the burst mode of protostellar accretion. The burst mode begins upon the formation of a centrifugally balanced disk around a newly formed protostar. It is comprised of prolonged quiescent periods of low accretion rate which are punctuated by intense bursts of accretion (typically ~ 10^{-4} Msun yr^{-1}), during which most of the protostellar mass is accumulated. The accretion bursts are associated with the formation of dense protoplanetary embryos, which are later driven onto the protostar by the gravitational torques that develop in the disk. Gravitational instability in the disk is driven by continuing infall from the cloud core envelope. We show that the disk mass always remains significantly less than the central protostar mass throughout this process. The burst phenomenon is robust enough to occur for a variety of initial values of rotation rate, frozen-in (supercritical) magnetic field, and density-temperature relations. Even in cases where the bursts are nearly entirely suppressed, a moderate increase in cloud size or rotation rate can lead to vigorous burst activity. We conclude that most (if not all) protostars undergo a burst mode of evolution during their early accretion history, as inferred empirically from observations of FU Orionis variables.

Using RR Lyrae Variable Stars to Probe the Kinematic Signature of the Sagittarius Stream
Oct 18, 2007 | AAC 123 | 3:15 PM
Ron Wilhelm, Texas Tech

RRLyrae variable stars in the halo of our Galaxy are excellent kinematic tracer probes of halo substructure because the characteristics of their light curves allow them to be identified unambiguously. The problem with using these stars to probe the general halo field is the large amount of telescope time required to confirm variability for a population which is spread out across the entire sky.

I will present a brand new technique which uses only two epochs of observation, one photometric and one spectroscopic to identify RR Lyrae stars within the Sloan Digital Sky Survey (SDSS)and the Sloan Extension for Galactic Understanding and Exploration (SEGUE). With this technique it is possible to achieve a discovery efficiency of ~85% when compared to published variables within the SDSS. We find similar efficiencies from follow up observations at McDonald observatory and by comparison to SDSS stars with multiple spectroscopic observations.

The relative purity of the resulting sample allows us to probe the kinematics of the Sagittarius galaxy, tidal stellar stream. I will present new kinematic results for the leading and trailing arms of the Northern Steam which to date have never been explored. These results will ultimately help to place stronger constraints on theoretical models of the stream and on the shape of the Galactic dark matter halo.