Department of Astronomy Colloquia Schedule for Fall 2009
University of Texas at Austin

Sept. 1st

Ramón J. García López, Instituto de Astrofísica de Canarias
"Technology in Astrophysics: The IAC's Experience"

Instrumentation developments for ground-based and space observatories are in the
front-end of today's technologies. I will review in this talk the experience achieved by
the IAC (Instituto de Astrofísica de Canarias) in this matter and our involvement in
present-day projects for the Canary Islands, Chile and space.

Sept. 10th

Sukanya Chakrabarti, University of California, Berkeley
"Tidal Imprints of Dark Sub-Halos on the Cold Gas in Galaxies"

I will discuss a new analysis of the observed perturbations in the HI disk
of the Milky Way (Chakrabarti & Blitz 2009). Through analysis of a large
set of high resolution hydrodynamical simulations, I find that the
best-fit to these perturbations is produced by a perturber that tidally
interacted with the Milky Way disk, having a mass one-hundredth of the
Milky Way, and a pericentric approach distance of 5 kpc. I show that under
certain conditions one can break the degeneracy between the mass and the
pericentric approach in the evaluation of the tidal force to directly
determine the masses of satellites. This is a new method of determining
the masses of satellites and can provide an independent method of
characterizing the dark sub-halo population. Secondly, I use my radiative
transfer code RADISHE to observe simulations (both of quiescently evolving
and tidally interacting galaxies). I calculate the SEDs and images of
these simulations to compare to observed star formation profiles and the
IR emission in external galaxies.

Sept. 15th

No talk scheduled.

Sept. 22nd

Lisa Prato, Lowell Observatory
"The Youngest Extrasolar Planets"

The detection of planets orbiting 1 to 2 million year old T Tauri stars and the
determination their properties will provide a solid basis for advancing planet
formation theory. Our young planet radial velocity survey at McDonald
Observatory's 2.7 m Harlan J. Smith telescope has yielded a number of
promising extrasolar planet candidates orbiting young targets in the Taurus
star forming region. Follow up infrared observations to date have revealed
two cases in which we were misled by the presence of spots on rapidly rotating,
active, young stars, and one case of what appears to be a bona fide,
newly-formed planet with a mass of about 6 M_Jupiter and a period of 8.3 days.
This discovery sets the lower age limit on either the formation and/or the
migration of hot Jupiters around low-mass stars.

Sept. 29th

No talk scheduled.

Oct. 2nd

Special Event: The Texas Planetary Science Symposium

Oct. 6th

No talk scheduled.

Oct. 13th

Mark C. Lewis, Trinity University
"Saturn's Rings: Moonlets, Silicates, and Origins"

The Cassini probe has now been in orbit around Saturn for more than five
years returning a treasure trove of data from its many instruments. The
data from Cassini, combined with modeling work has answered many
questions. It has also reopened debate on some of the most fundamental
questions, including the origins of the rings themselves. This walk
will look at numerical modeling work that I have been doing on moonlets
and silicates in Saturn's rings and tie these in with observations and
the debate about ring origins.

Oct. 20th

Special Event: Frank N. Bash Symposium 2009 (Oct 18-20)

Oct. 27th

Kevin L. Luhman, Pennsylvania State University
"The Origin of Brown Dwarfs"

The origin of brown dwarfs is a mystery because standard theories of star formation
cannot easily create objects at such low masses. I will review the current state of
observational and theoretical work on understanding how brown dwarfs form. I will
first describe the latest measurements of various properties of brown dwarfs,
including their initial mass function, binarity, circumstellar environment (disks,
accretion, envelopes), and spatial and velocity distributions at birth, and I will then
compare these data to the predictions of theories for the formation of brown dwarfs.

Oct. 27th

Antoinette de Vaucouleurs Public Lecture
Rashid Sunyaev, Max-Planck Institute for Astrophysics
"The Richness and Beauty of the Physics of Cosmological Recombination"

The initial temperature of radiation in our Universe was very high and hydrogen and
helium were completely ionized. At redshifts z ~ 1400 the temperature dropped to
3800 K and, according to the Saha equation, the recombination of hydrogen should occur.
In reality this process is strongly delayed and some frozen amount of electrons should be
present till the reionization of the Universe at z ~10.

Process of recombination defines the position and the width of the last scattering surface
which is crucial for the formation of the observed angular fluctuations of cosmic microwave
background radiation (CMB), acoustic peaks and barionic oscillations in the distribution
of galaxies and clusters of galaxies.

The recombination of hydrogen occurs under conditions of very low density and in the
presence of black body radiation. As a result, usually insignificant atomic processes begin
to play a role. They influence the shape of CMB acoustic peaks at a level which will be
detectable by the "Planck Surveyor" spacecraft and we should take them into account
when estimating the key parameters of the Universe from CMB data.

The recombination of hydrogen and helium leads to the appearance of recombinational
lines in millimeter, centimeter and decimeter spectral bands. Observations of these lines
will make it possible to check the predictions of the big bang recombination theory and will
open a possibility to measure directly the density of barions, the CMB monopole temperature
and specific entropy of the Universe, to check the presence of any significant energy release
in early Universe (for example due to decay of unknown particles). Observations of helium
recombination lines originated at redshifts 6000 and 2500 will open a way to measure the
prestellar abundance of helium in the Universe.

Oct. 28th

Antoinette de Vaucouleurs Memorial Lecture
Rashid Sunyaev, Max-Planck Institute for Astrophysics
"Cosmic Microwave Background, Clusters of Galaxies and Cosmology"

Rich clusters of galaxies contain thousands of galaxies moving in a huge potential well
with velocities exceeding 1000 km/s. They are filled with dark matter and extremely hot
intergalactic gas. This gas diminishes the brightness of CMB in the directions towards
clusters of galaxies opening new way to discover distant unknown clusters. The spectrum
of the brightness change is unique and does not depend on the redshift. Similarly the
surface brightness of the cluster in the microwave spectral band does not depend on
the redshift. This opens a way to observe the most distant clusters in the Universe,
to study the key parameters of our Universe, and even to measure the peculiar velocities
of clusters of galaxies in respect to the unique coordinate frame where CMB is isotropic.

Planck Surveyor Spacecraft, South Pole Telescope, Atacama Cosmology Telescope,
APEX, AMI and SZ-Array observed hundreds of clusters using this method. Using the
data of microwave surveys and results of the new Russian-German space project
SPEKTR-X/eRosita planning to map whole sky in X-Rays we will get an opportunity
to construct the "curve of growth" for clusters of galaxies and to measure the baryonic
acoustic oscillations in the distribution of clusters in the relatively old Universe.

The X-Ray calorimeters and hot gas observations in the lithium-like Fe57 hyperfine
structure line with wavelength 3.06 mm together with broad band microwave
measurements will give a unique information about about turbulence and bulk
motions in the hot intercluster gas.

Oct. 29th

Special Event: Texas Cosmology Network Meeting 2009 (Oct. 29-30)

Nov. 3rd

Beatrice M. Tinsley Visiting Professor in Astronomy
Eliot Quataert, University of California, Berkeley
"The Birth of Neutron Stars and Black Holes in Gamma-ray Bursts"

Gamma-ray bursts (GRBs) have long been among the most enigmatic of
astrophysical transients. Observations during the past decade have
led to a revolution in our understanding of long-duration GRBs,
associating these events with the core-collapse of massive stars.
However, only in the past few years have the host galaxies of
short-duration GRBs been established, confirming that these arise from
a separate progenitor population; the leading model for such events is
the merger of two compact objects (e.g., a neutron star and a black
hole) although alternative possibilities remain viable (e.g., the
accretion induced collapse of a white dwarf to a neutron star). In
this talk, I will describe theoretical models for both long and
short-duration bursts, emphasizing several outstanding problems.
Short GRBs are particularly interesting since compact object mergers
are the primary target for km-scale gravitational wave observatories
such as Advanced LIGO. I will describe possible electromagnetic
counterparts to these gravitational wave sources.

Nov. 10th

Benjamin Weiner, Steward Observatory, University of Arizona
"Infrared-luminous galaxies and their evolution:
what, where, and maybe some of how"

Infrared-luminous galaxies are powered by star formation or active
galactic nuclei, but emit much of their light as radiation reprocessed
by dust into the far infrared. The most massive starbursts in both
the local and high redshift universe manifest themselves as
ultraluminous infrared galaxies. This class of galaxies was
discovered by IRAS; observations with Spitzer have revealed many
IR-luminous galaxies from z=0 to z=1 and yielded measurements of the
evolution in global IR luminosity density. However, it remains
controversial what IR-luminous galaxies at z=1 are, and what they will
evolve into. Are IR-luminous galaxies at high redshift mostly galaxy
mergers, as they are at low redshift? Are ultraluminous IR galaxies
strongly clustered, and can we infer whether they must evolve into
cluster galaxies today? I will discuss these questions on IR-luminous
galaxy properties and clustering using data from Spitzer/MIPS, HST,
and the DEEP2 redshift survey.

Nov. 17th

Christian Marois,  NRC Herzberg Institute of Astrophysics
"Imaging Planets Orbiting Other Stars: The HR8799 Multi-Planet System"

Almost 15 years ago the first unambiguous direct detection of a substellar object
around a star (Gl229B) was made. Several teams have since then pursued ambitious
adaptive optics surveys on large telescopes, but only several brown dwarfs and a few
possible candidate planets have been detected so far at generally wide >100 AU
separations - it is unlikely that these have formed in a disk like the planets of our
solar system and are probably the result of the binary star formation process. The
essentially null result of these surveys, in contrast with the very successful radial
velocity searches <5 AU, is suggesting that massive Jupiter-like planets are rare
>20 AU around stars. The year 2008 marks then end of this long drought with the
direct detection of planets around A-type stars. One of these discoveries, the
HR8799 planetary system made at the Gemini North and Keck telescopes, is
the first multi-planet system portrait and also the first direct detection of thermal
emission of confirmed planets in orbit around a star. This system also shows
convincing evidences that the three planets formed in a disk. The HR8799
system discovery marks an important step forward in the direct characterization
of Jovians to Earth-like planets with future instrumentations and large ELTs.
I will describe the HR8799 system discovery, new 2009 results and what we
can expect in the near future with new generation adaptive optics systems
and 30-m class telescopes.

Nov. 24th

Daisuke Nagai, Yale University
"Cosmology and Astrophysics with Galaxy Clusters"

Clusters of galaxies are unique and powerful probes of cosmology and astrophysics,
promising to provide new insights into the nature of dark energy and dark matter to
the physics of galaxy formation. The study of galaxy clusters combines the richness
of plasma physics with the predictive power of modern cosmological models to explain
remarkable new observational results. In this talk, I will describe recent advances
in theoretical and intensive numerical modeling of galaxy cluster formation to interpret
recent X-ray and Sunyaev- Zel'dovich Effect cluster surveys. Finally, I will discuss
outstanding issues and future directions in this area.

Dec. 1st

Juna A. Kollmeier, Carnegie Observatories
"Probing the Inner and Outer Milky Way"

The Milky Way provides an opportunity for a close-up investigation of the complex
processes of galaxy and star formation. I will discuss recent efforts to do this by using
rare, but important, probes of these phenomena. In the first portion of the talk I will
present results on hypervelocity stars primarily from the Sloan Digital Sky Survey.
The distribution of these stars, in physical properties and in space, allows us to place
interesting limits on star formation and dynamics at the Galactic Center as well as
the possibility to constrain the shape of the Milky Way's dark matter halo. I will
discuss progress we have made toward these goals. In the second portion of the
talk, I will discuss how one can use RR Lyrae stars to probe the outer halo of the Milky
Way and find new and distant substructures which are difficult to probe by other means.
Our recent confirmation of a distant structure in RR Lyrae stars highlights the power
of this approach to unraveling the outer halo and showcases exciting possibilities
for future all-sky time-domain surveys.

Last Modified: December 2009