Dept. of Astronomy Colloquia Schedule for Spring 2008
University of Texas at Austin

Jan. 15th

Jenny E. Greene
Princeton University
"Local Galaxies with Radiating Black Holes"

The evolution of supermassive black holes and galaxies are apparently inextricably
linked, and we might hope to gain unique insight into the nature of their connection
by studying galaxies with currently accreting black holes. The study of active host
galaxies has a long history; I focus here on three innovative experiments that exploit
both the recent availability of large spectroscopic surveys such as the SDSS as well
as improved techniques to estimate black hole masses in active galactic nuclei (AGNs).
The first uses HI observations of local AGNs to measure their circular velocities and
disturbance levels. The second focuses on luminous narrow-line AGNs, where we have
a direct view of the host galaxy, to look for direct evidence of large-scale outflows,
possibly driven by the nuclear activity. Finally, I examine the host galaxies of AGNs
selected to have the lowest known black hole masses known, a regime in which the
correlations between black holes and bulges must begin to break down. I discuss
the implications for AGN feedback, and the possibility of observing continuing
evolution in the relations between black hole mass and bulge properties at the
present epoch.

Jan. 22nd

Special Event: Beatrice M. Tinsley Visiting Professor in Astronomy

Ramesh Narayan  Harvard University
"Measuring Black Hole Spin"

An astrophysical black hole is completely described with just two parameters:
its mass and its dimensionless spin. A few dozen black holes have mass
estimates, but until recently none had a reliable spin estimate. The first spins
have now been measured for black holes in X-ray binaries. The talk will summarize
the current state of the field and will discuss prospects for the future.

Jan. 29th

Todd Thompson
  Ohio State University
"Feedback in Starburst Galaxies"

I will describe a set of projects aimed at developing a physical picture of the
feedback and regulation processes in the ISM of starburst and ultra-luminous
infrared galaxies. The UV radiation produced by massive stars in the ISM of
starbursts is absorbed, scattered, and reprocessed into the IR by dust grains.
The associated radiation pressure may provide the dominant vertical support
against gravity. I will discuss the implications of this important feedback process.
Because the disk radiates at its Eddington limit (for dust), starbursts supported
by by radiation pressure achieve a characteristic radiative flux and their "Schmidt
Law" for star formation changes qualitatively with respect to normal star-forming
galaxies. I will also describe observational and theoretical constraints on the
magnetic field strength in starbursts, with direct implications for the origin of the
FIR-Radio correlation, the shape of the radio spectra of starbursts, and their
and their observability at GeV energies by GLAST. Lastly, I will discuss the
starburst contribution to the diffuse extragalactic gamma ray and radio backgrounds.

Feb. 5th

No talk scheduled.

Feb. 12th

Special Event: Beatrice M. Tinsley Visiting Professor in Astronomy (visit: Feb 11-21)

Ivan Hubeny
  University of Arizona   Abstract
"From Stars (Planets) to Quasars: Modeling Radiation-Dominated
Objects in Astrophysics"
(host: Greg Shields)

Feb. 13th

Special Colloquium (visit: Feb. 13-14)

Klaus M. Pontoppidan
  California Institute of Technology (Caltech)
"Straddling the Snow Line: Water Vapor and Carbon-Containing
Molecules in Protoplanetary Disks at 1 AU"

The planet-forming zones (radii of 0.1 - 10 AU) of disks around young solar-type
stars is an active environment characterized by a rich chemistry and a complex
dynamical synergy between gas, dust ad potentially proto-planets. I will discuss how
how very high resolution infrared spectroscopy of warm molecular gas can provide
unique tests for models of the evolution of such disks. New results include the
detection of water vapor and OH in a large fraction of protoplanetary disks, showing
that the water molecule is abundant, not only beyond the snow line, but also in the
inner warm regions of the disk, suggesting that it is being replenished by inward
migration of icy bodies. I will also present the first results imaging molecular gas
in planet-forming zones at milli-arcsed resolution (or ~0.1 AU) using spectro-astrometry.
The technique is used to image the distribution and kinematics of gas inside the inner
dust gaps of so-called 'transition' disks, some of which have been suggested to harbor
newly formed planets. I will discuss how spectro-astrometry of molecular gas can be
used to distinguish between various gap formation mechanisms.

Feb. 19th

Nick Kaiser
  University of Hawaii - Institute for Astronomy
"The Pan-STARRS Wide Field Survey Project"

The Institute for Astronomy at the University of Hawaii is developing a large optical/near-IR
survey telescope system; the Panoramic Survey Telescope and Rapid Response System.
Pan-STARRS will employ 1.8m optical imagers, very large (7 square degree) field of view
and revolutionary 1.4 billion pixel CCD cameras with low noise and rapid read-out to provide
broad band imaging from400-1000nm wavelength. The project is proceeding in two phases:
PS1 is a single aperture system that has been deployed onHaleakala on Maui and will start
a 3.5 year survey in 2008. Support for operations is being provided by the PS1 Science
Consortium, which includes scientists in the US, the UK and in Germany. The full 4-aperture
system PS4 will be sited on Mauna Kea and will become operational following the end of
the PS1 mission. The data from Pan-STARRS will be reduced in near real time to produce
both a cumulative image of the staticsky and difference images, from which transient, moving
and variable objects can be detected. Pan-STARRS will be able to sca the entire visible sky
to approximately 24th magnitude in less than a week, and this unique combination of sensitivity
and cadence will open up many new possibilities in time domain astronomy. A major goal
for the project is to survey potentially dangerous asteroids, where Pan-STARRS will be able
to detect most objects down to 300m size, much smaller than the km size objects accesssible
to existing search programs. In addition, the Pan-STARRS data will provide a dramatic leap
in data quality and extent over existing wide-field image survey data that will be used to
advance our understanding of the formation of the Solar System, the Galaxy and the Cosmos
at large. In this talk I will describe the science drivers for the project, review the technical
design, the various scientific goals, and give an update on the progress that has been made
in commissioning the first telescope system.

Feb. 20th

Special Event: Beatrice M. Tinsley Visiting Professor in Astronomy (visit: Feb 11-21)

Ivan Hubeny
  University of Arizona
"Transiting Extrasolar Planets: A Key to Understanding their Physics
Chemistry, and even Meteorology"

Feb. 21st

Special Colloquium (visit: Feb. 21-22)

Seth L. Redfield
  University of Texas at Austin
"The Age of Exometeorology: Observing the Atmospheres
of Transiting Exoplanets"

High signal-to-noise ratio (S/N) and high spectral resolution observations of transiting
exoplanets provide an opportunity to measure the properties of exoplanet atmospheres
through transmission spectroscopy. I present the results of a large-scale program
which led to the first ground-based detection of absorption due to an exoplanetary
atmosphere. Observations were taken with the Hobby-Eberly Telescope (HET), which
is well suited for this type of program given its large mirror, high resolution spectrograph,
and queue scheduling. We observe significant additional absorption in the cores of
the neutral sodium doublet relative to the continuum, when in-transit observations are
compared to out-of-transit observations. Two tests are performed to confirm the detection:
(1) analysis of a strong control line that is predicted to show no absorption, and
(2) an empirical Monte Carlo analysis to quantify the impact of systematic errors. Physical
properties of the exoplanet atmosphere, such as atomic and molecular composition,
cloud altitudes, and wind speeds may be derived from the transmission spectrum. I will
discuss the richness of the acquired datasets and describe several complimentary
research projects. Observations of several other bright transiting systems are ongoing
with the HET, while future large telescopes will push research toward observations of
smaller atmospheres (e.g., terrestrial exoplanets), weaker spectral features (e.g., biomarkers),
and temporal variability (e.g., weather). A growing sample of transiting exoplanets coupled
with continued observational achievements and capabilities are just beginning to make
direct comparisons of physical characteristics of exoplanet atmospheres possible,
ventually leading to comparative exometeorology.

Feb. 26th




Special Colloquium (visit: Feb. 26-27)

Yoram Lithwick Canadian Institute for Theoretical Astrophysics (CITA)
"Dynamics of Protoplanetary Disks: Vortices and Turbulence"

Protoplanetary disks are gaseous accretion disks around young stars. I will show
how, in hydrodynamical accretion disks such as these, vortices form out of a nonlinear
instability. I will also show that a vortex's ultimate fate in 3D depends on whether
it is weak or strong. Weak vortices live essentially forever. Strong vortices decay into
turbulence via a 3D instability. One interesting implication is that in protoplanetary
disks dust can be trapped by weak vortices, triggering planet formation. A second
implication is that strong vortices can be responsible for the turbulence that makes
these accretion disks accrete.

Feb. 28th

Special Colloquium (visit: Feb. 28-29)

Sarah E. Robinson University of California / Lick Observatory
"Chemistry of Giant Planet Formation: Future Directions in Theory
and Observations"

What role do ices play in giant planet formation? New chemical models of the solar
nebula show that in addition to water ice, Saturn's feeding zone contains solid ammonia,
methane, and hydrogen cyanide. These simulations cann account for both Saturn's large
core (<= 22 Earth masses) and its formation at a large distance from the sun, where
solid core growth is slow. Organic ices incorporated into planetesimals help boost Saturn's
core mass and growth rate so that the planet forms in only 3.4 Myr, similar to the observed
median protostellar disk lifetime.

Models of planet formation in ice-rich regions can be extended to other planets with heavy
cores such as HD 149026 b, Neptune and Uranus. Core accretion simulations based on a
a disk with twice solar metallicity allow HD 149026 b to form in only 1.6 Myr, leaving ample
time for migration into the current short-period, transiting configuration.

Mar. 4th

Nicole P. Vogt
  New Mexico State University (NMSU)
"Nine Billion Years of Galaxy Evolution: Disentangling Recent
Evolution and Selection Biases in Disk Galaxies"

We review the status of current observations of the fundamental parameters of intermediate
redshift (z < 1.3) disk galaxies. Modern instrumentation enables detailed measurements
of galaxy luminosity, morphology, kinematics and mass, in both optical and the infrared
passbands. By studying well known star formation indicators, the internal velocity structure
and star formation rates of galaxies can be traced though this entire redshift regime.
The combination of throughput and optimum seeing conditions yields spectra which can
be combined with high resolution multiband imaging to explore the evolution of galaxies
of various morphologies, and to place constraints on current models of galaxy formation
and star formation histories.

Out to redshifts of unity, these data form a high redshift Tully-Fisher relation that spans four
magnitudes and extends to well below L*, with no obvious change in shape or slope with
respect to the local relation. A comparison of disk surface brightness betwen local and high
redshift samples yields an offset in accordance with distance-dependent surface brightness
selection effects, as can the apparent change in disk size with redshift for disks of a given
mass. The effects of imaging and spectral selection are shown to be significant, dependent
not only upon the broad-band luminosity and surface brightness of targets but also a strong
function of emission line strength and spectral flux distributions. These results provide further
evidence for modest increases in luminosity with lookback time for the bulk of the observed
field spiral galaxy population.

Mar. 5th

Special Colloquium (visit: Mar. 5-6)

Michael P. Muno California Institute of Technology (Caltech)
"Identifying Black Holes and Neutron Stars in Order to Understand
How They Formed (or, Making Dead Stars Talk)"

I will describe my observational programs to assemble samples of black holes and
neutron stars. I am using these samples to address several open questions, including:
Which stars from black holes? What fraction of neutron stars ar born with extremely
bestrong magnetic fields (B > 10^14G)? What is the distribution of masses for stellar
black holes, and why have we found so few with masses just larger than the maximum
mass of a neutron star? I will report the progress I am making by combining X-ray images
from the Chandra Observatory with ground-based infrared follow-up, and briefly describe
the potential of planned X-ray observatories, such as the Nuclear Spectroscopic Telescope
Array (NuSTAR).

Mar. 18th

Harold 'Hal' F. Levison
  Southwest Research Institute/Dept. of Space Studies
"The Early Dynamical Evolution of the Outer Solar System: A Nice Story"
(visit: Mar. 16-19)

The orbits of the giant planets in our Solar System have changed significantly
since the planets formed. This is made clear by the complex and excited dynamical
state of the small body reservoirs. In this talk, I will discuss a new model for the early
evolution of the outer Solar System. In this scenario, the giant planets start in a very
compact configuration that went violently unstable some 600 Myr after the Solar System
formed. This model explains, for the first time, many of the observed characteristics,
including (1) the orbits of the giant planets, particularly the eccentricities of Jupiter
and Saturn, (2) the structure of the trans-Neptunian region, (3) the origin of the Trojan
and Hilda asteroids, and (4) the late heavy bombardment of the Moon.

Mar. 25th

Eiichiro Komatsu
  University of Texas at Austin
"The 5-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations:
Cosmological Interpretation"

We have just announced the results from 5 years of observations of the Wilkinson
Microwave Anisotropy Probe (WMAP) on March 5, 2008. In this talk I will give a
summary of significant new findings, as well as the cosmological interpretation
of the WMAP 5-year data.

Apr. 1st

No talk scheduled.

Apr. 4th

Special Event: Beatrice M. Tinsley Visiting Scholar in Astronomy (visit: Apr. 2-5)

Jane Arthur  Centro de Radioastronomia y Astrofisica, UNAM
"HII Regions for the 21st Century"

Textbook spherical HII regions do not bear much resemblance to reality, e.g. observed
HII regions such as the Orion Nebula. Recent modeling work has gone a long way towards
including the physical processes and ambient conditions necessary to enable meaningful
comparisons, both morphological and spectral, to be made. In this talk, I describe these
endeavours and discuss improvements to the models that could be made in the future.

Apr. 8th

Special Event: Beatrice M. Tinsley Visiting Scholar in Astronomy (visit: Apr. 6-18)

Philip F. Hopkins  Harvard-Smithsonian Center for Astrophysics
"Dissipation in the Formation of Elliptical Galaxies:
Putting our Understanding of Spheroid Formation to the Test"

We generally believe that galaxy spheroids are formed from the merger of (initially)
disk-dominated systems, but for ~30 years this idea has been challenged on the
basis that ellipticals are observed to be much more dense than spirals. Dissipation --
the formation of new stars in a gas-rich starburst -- has generally been invoked as the
means to solve this dilemma, but simulations are only just reaching the point where
they can include this in a self-consistent manner and make objects that look like "real"
ellipticals. Meanwhile, although observations are probing nearby galaxies with incredible
detail, there is no well-established way to actually estimate the quantity desired to test
these models and measure the most important element of bulge formation history: how
much gas dissipation was involved in their formation. By combining new generations of
numerical simulations with exceptional space and ground-based observations, we show
not only that can we reproduce the properties of observed ellipticals, but we can use the
simulations to understand how the profiles of ellipticals are shaped by dissipation and
merger history. This allows us to construct robust, empirical decompositions, separating
the observed systems into violently relaxed stars and those formed dissipationally.
The dissipational-dissipationless breakdown has dramatic consequences for galaxy
properties, and allows us to test the key elements of any model for the origin of
ellipticals and the fundamental plane scalings of mergers.

Apr. 10th

Special Event: Beatrice M. Tinsley Visiting Scholar in Astronomy (visit: Apr. 6-18)

Philip F. Hopkins Harvard-Smithsonian Center for Astrophysics
"Quasars and Galaxy Mergers: Fueling, Feedback, and Evolution"

Most models of galaxy formation now invoke (or even require) some form of feedback
and interplay between supermassive black holes and galactic gas, and observations of
quasars increasingly probe their host galaxy properties and fueling mechanisms. But we
know disturbingly little about the details and implications of the 'overlap' between these
areas. I'll discuss work we've done to explore evolutionary models for starbursts, quasars,
and speroidal galaxies in which supermassive black holes play a dominant role. In this
picture, mergers between gas-rich galaxies drive nuclear inflows of gas, producing intense
starbursts and feeding the growth of supermassive black holes. During this phase, the
black hole is heavily obscured, but feedback energy from its growth expels the gas,
rendering the black hole briefly visible as a bright, optical source, and eventually halting
accretion. This class of models provides a natural explanation for correlations between
black hole bass and host galaxy properties, but there arise a number of other interesting,
and in some ways unexpected implications for the nature of quasar lifetimes and lifecurves,
the impact of quasar feedback on the host galaxy, and the interpretation of the quasar
luminosity function. Moreover, this is almost certainly no the only way to make an AGN:
I'll discuss alternative models of quasar fueling, where and when they are expected to
be important, and how observers might be able to tell the difference.

Apr. 14th

Fred K. Y. Lo
Director, National Radio Astronomy Observatory (NRAO)  
"Mega-masers, Dark Energy and the Hubble Constant"

Powerful water maser emission (water mega-masers) can be found in accretion disks in the nuclei
of some galaxies. Besides providing a measure of the mass at the nucleus, such mega-masers can
be used to determine the angular diameter distance to the host galaxy, based on a simple model. We
will explain the importance of determining the Hubble Constant to a high accuracy for constraining the
equation of state of Dark Energy and describe the Mega-maser Cosmology Project that has the goal
of determining the Hubble Constant to ~3%. We will also present the scientific capabilities of the
current and future NRAO facilities:
ALMA, EVLA, VLBA and GBT, for addressing key astrophysical

Apr. 22nd

Ehud Nakar
  California Institute of Technology (Caltech) (visit: Apr. 21-25)
"The Search for the Origin of Short Gamma-Ray Bursts"

Two types of Gamma-Ray Bursts (GRBs) are observed: short duration and long duration.
While it is known for several years now that long GRBs are the emission of cosmic
ultra-relativistic outflows that are launched following the collapse of massive stars, the
origin of short GRBs remained a complete mystery until recently. The breakthrough came
on the summer of 2005 with the first detection of short GRB afterglows, long wavelength
emission that follows the burst of gamma-rays. These observations established that short
GRBs are cosmological relativistic explosions as well, but unlike their long relatives
they do not originate from massive stars. Instead, observations suggest that double neutron
star mergers may be the progenitors of short GRB, in which case they are the electromagnetic
counterparts of a strong gravitational-wave signal. The search for the progenitors of
short GRBs, following the recent discoveries, is reviewed.

Apr. 29th

Special Event: Beatrice M. Tinsley Visiting Scholar in Astronomy (visit: Apr. 20 - May 04)

Jonathan McKinney  Harvard-Smithsonian Center for Astrophysics
"Magnetically-Driven Ultrarelativistic Jets from Rotating Black Holes"

We now understand the basic mechanisms for astrophysical systems, such as accreting
black holes, to generate moderately relativistic outflows from x-ray binaries and active
galactic nuclei. An unsolved theoretical problem is how gamma-ray burst (GRB) engines
are able to produce Lorentz factors of roughly 400 and opening angles of a few degrees.
I will review the mechanisms for how jets are produced, discuss recent advances from
general relativistic magnetohydrodynamical simulations of accreting rotating black holes,
and describe recent theory and simulations that show how the Lorentz factors, opening
angles, and jet structures might naturally be determined for GRBs.

May. 6th

Special Event: Beatrice M. Tinsley Visiting Scholar in Astronomy (visit: May 5-16)

Travis Barman  Lowell Observatory, Flagstaff, Arizona
"Exploring the Atmospheres of Extrasolar Planets"

Planets are now routinely found around other stars and the flood of discoveries shows
no signs of abating. A growing number of planetary systems are currently being discovered
in very accommodating orbits, opening up new possibilities for more detailed study of
distant atmospheres. Cleverness and new technology have been combined to allow us
to "see" the atmospheres of distant worlds for the first time. This talk will summarize some
of the recent discoveries and describe how theoretical models are being used to extract
information about atmospheric chemical composition, thermal structure, and global

May. 20th

Special Event: Beatrice M. Tinsley Visiting Scholar in Astronomy (visit: May 14-31)

Rene Goosmann  Astronomical Institute, Acadamy of Sciences, Czech Republic
"Exploring the Innermost Accretion Regions of Supermassive Black Holes"

The regions closest to the supermassive black holes (SMBHs) in AGNs must be explored
in the X-ray range. The innermost part of the accretion disk reaches down to the last
marginally stable orbit of the SMBH. Above the disk, co-orbiting magnetic flares are
expected to occur. I investigate the spectral appearance of such flares and the effect of
these on the radiation that is reprocessed by the disk. I present the results of modeling
involving detailed radiative transfer simulations and ray-tracing to account for general
relativistic and Doppler effects. I show how this modeling can be applied to current and
future AGN spectra and variability data. It delivers important constraints on the irradiation
pattern of the accretion disk, and on the mass and spin of the SMBH.

May. 27th

Special Event: Beatrice M. Tinsley Visiting Scholar in Astronomy (visit: May 14-31)

Rene Goosmann Astronomical Institute, Acadamy of Sciences, Czech Republic
"Using Polarization to Probe Unresolved Structure of AGNs and Other Objects"

The structure of many astrophysical objects (AGNs, supernovae, X-ray binaries, and
gamma-ray bursts) cannot be directly resolved yet. I discuss various mechanisms by
which scattered line and continuum radiation is polarized, and show how polarization
measurements allow profound insights to be gained into the geometrical structure and
the dynamics of AGNs and other objects. Using the Monte Carlo radiative transfer code
STOKES, the polarization signatures of various reprocessing regions around compact
objects can be modeled. The radiative coupling between individual scattering regions
can be complex but is correctle modeled with STOKES because it automatically includes
multiple scattering effects. Recently we introduced the new technique of polarization
reverberation mapping. This method exploits the time-dependence of the polarization
signal and allows us to measure distances between radiation sources and polarizing

Last Modified: May 2008