Dept. of Astronomy Colloquia Schedule for Fall 2006
University of Texas at Austin

September 12th

Daniel Proga
  University of Nevada at Las Vegas
Numerical Modeling of Magnetohydrodynamic Accretion Flows
in Gamma-ray Bursts
I present results from numerical simulations of a magnetized flow in
the vicinity of a black hole in the context of the collapsar model for GRBs.
The simulations show that after an initial transient, the flow settles into
a complex configuration of several distinct flow components.
I discuss the nature and connection between these components,
in particular between the inflows and related outflows.
I also discuss how and under what conditions the collapsing stellar
can trigger a very strong and fast outflow that can become a relativistic jet.

September 19th

Eric Becklin
  University of California at Los Angeles
SOFIA: Stratospheric Observatory for Infrared Astronomy
The SOFIA project to develop and operate a 2.5-meter infrared telescope in
a Boeing 747-SP is in the final stages of development. First science
flights will begin in 2009, with the observatory designed to operate for
over 20 years. Status of the development and technical issues will be
discussed along with the expected sensitivity, and first light science
instruments. Also discussed will be examples of the science to be carried
out and opportunities for the science community to use SOFIA. On the
science side, I will also discuss our recent high angular resolution
results on the Galactic Center with Keck laser adaptive optics.

September 26th

Jerry Sellwood  Rutgers University
Galaxy Halos
The LCDM model of structure formation makes specific predictions for the density
of dark matter halos in galaxies. I review recent work, which seems to indicate that
halo densities are much lower than predicted, and discuss possible resolutions of
this discrepancy.

October 10th

Jason X. Prochaska  University of California, Santa Cruz
Characterizing the Interstellar Medium in the Host Galaxies of GRBs
I will discuss observations on the interstellar medium of the galaxies hosting long duration
gamma ray bursts.These observations reveal the metallicity, dust-to-gas ratio, ionization state,
molecular fraction, and density of the gas. In addition to providing insight into the progenitors of

GRBs, the observations detail the gas which fuels star formation in young, high z galaxies.

October 17th

Wendell Horton  University of Texas at Austin
Magnetic Reconnection from Plasma Winds on Magnetospheres

October 24th

Chuck Claver  National Optical Astronomy Observatory (NOAO)
The Large Synoptic Survey Telescope
The Large Synoptic Survey Telescope (LSST) is a planed digital survey facility for the
purpose of exploring the nature of dark energy and dark matter, opening the time domain
over a large portion of the night sky, taking a census of the small bodies in the solar
system, and understanding the stellar content and formation history of the Milky Way.
The survey will map 20,000 square degrees in six broadband filters, u, g, r, i, z and Y,
not just once but multiple times over a ten-year span with the entire survey area covered

in at least one filter every 3 - 4 nights. The LSST uses a modified Paul-Baker 3-mirror
optical design with 8.4-m primary, 3.4-m secondary and 5-m tertiary mirrors. The 3-
mirror telescope feeds a 3-element refractive corrector to produce 3.5-degree diameter

field of view over a 64-cm flat focal surface. The 9.6 square degree images are recorded
with a 3.2 billion pixel camera with a resolution of 0.2 arcseconds per pixel. The etendue
(collecting area times field of view), a measure of survey capability, for the LSST is
319 m2deg2, many times that of any other existing or proposed facility. Each night, 15
terabytes of images will be processed in near real time for transient detection, producing
alerts delayed by 30 seconds. Each year the survey will archive 15 petabytes of images.
Over the course of the 10-year survey, 20 object catalogs (25 petabytes) will be
released - one every six months. The final image archive will be approximately 65 petabytes,
making the LSST the largest freely accessible database worldwide.

November 7th

Smita Mathur  Ohio State University
UV and X-ray Observations of the Warm-Hot Intergalactic Medium
Hydrodynamic cosmological simulations predict that most of the baryons at low redshift reside
in warm-hot intergalactic medium, WHIM. One of the few prospects for detecting this shock
heated, low density gas is via the "X-ray forest" of absorption lines it should produce in quasar
spectra. Such observations are now possible with Chandra X-ray Observatory. I will describe
recent efforts to trace the WHIM and determine its physical properties, with Chandra as well as
with HST and FUSE, and discuss the implications towards the missing baryon problem. I will
also describe the attempts to detect the Local Group baryons with X-ray and UV observations.

November 14th

Isaac Shlosman  University of Kentucky
Assembling Galactic Disks in Dark Matter Halos
Dark matter halos which form in cosmological numerical simulations appear to be universally
triaxial, while those in the nearby universe are probably axisymmetric. I will discuss some
implications of the host halo shapes on formation and evolution of galactic disks, as well
as the feedback from the embedded disks on the surrounding halos.

November 21st

Jason S. Kalirai  University of California Observatories / Lick Observatory
The Stellar Populations of the Andromeda Spiral Galaxy
Simulations of hierarchical galaxy formation suggest that large galaxies such as the Milky
Way and M31 should contain extended stellar halos that are chemically distinct (more metal
poor) from the inner bulge. Yet, two decades of intensive effort have failed to reveal any such
population of our nearest neighbor, M31. We report on the results from a photometric and
spectroscopic survey of red giant branch (RGB) stars over a large expanse in the Andromeda
spiral galaxy (M31). Using a combination of photometric and spectroscopic diagnostics, we
isolate bonafide M31 RGB stars in its bulge, disk, and halo at projected distances of R = 12 - 160
kpc from the center of M31. Along the major axis out to 30 kpc, we find clear evidence for a

kinematically cold, metal-rich disk-like population. Out to 30 kpc along the minor axis, we
confirm earlier studies and find that M31 is dominated by a metal-rich, R^1/4 surface
brightness (de Vaucouleur profile). However, beyond this distance, the brighness profile of
M31 RGB stars lies well above an outward extrapolation of the inner bulge-like profile and
is consistent with an R^-2.5 surface brightness profile (i.e. an extended, power-low halo)
We measure both spectroscopic and photometric metallicities for this new population and
find that, in fact, the outer halo of M31 is metal-poor relative to the inner bulge. Taken together,
these results suggest that the bulge to halo ratio of M31 is much larger than the Milky Way.

November 28th

Bill Welsh  San Diego State University (SDSU)
Transiting Extrasolar Planets
Over 200 extrasolar planets have been discovered as of late 2006. Fourteen of these are
particularly important because they transit (eclipse) their host stars. Transiting systems provide
a wealth of information about exoplanets. Photometry of the transit allows us to determine
the orbital inclination and radius of the planet. Combined with the star's reflex orbital velocity
we can estimate the planet's mass and density, which tells us whether it is a terrestrial or
gas giant planet. Precise photometry allows us to measure the planet's temperature, and in
principle it can be used to detect small objects such as satellites and rings around the planet,

as well as find other planets in the system via their gravitational perturbations of the transiting
planet's orbit. In addition, transits allow unprecedented measurements of the host star itself,
e.g., limb darkening, differential rotation, and spin-orbit axes alignment. In this talk I will briefly
review what we have learned from transiting exoplanets and discuss my work on (1) modelling
the transits of HD 209458b and (2) the possibility of detecting Earth-like planets via the
Rossiter effect.

December 5th

Anna Frebel  University of Texas at Austin
Abundance Analysis of Bright Metal-Poor Stars from the
Hamburg/ESO Survey

The most metal-poor objects in the Galactic Halo provide important tools to study the
chemical evolution of the Milky Way and the early Universe. This thesis enlarges
the sample of known metal-poor stars with [Fe/H]<-2.5. A sample of 1777 bright (10<B<14)
metal-poor candidates with partially saturated spectra was drawn from the digitized
Hamburg/ESO objective-prism survey. Metallicity estimates [Fe/H] have been obtained
from medium-resolution (~2A) follow-up spectra. 145 stars were found to have [Fe/H]<-2.0.
Of these, 79 have [Fe/H]<-2.5, while 17 have [Fe/H]<-3.0. A detailed abundance analysis

based on high-resolution spectroscopy (R~60,000) has been carried out for two stars
(HE 1327-2326 and HE 1523-0901) of the bright sample and one object (HE 1300+0157)
taken from the faint HES sample of Christlieb and collaborators. The results will be
presented in detail.

Last Modified: January 2007