Dept. of Astronomy Colloquia Schedule for Spring 2009
University of Texas at Austin

Jan. 27th

Norman Murray
Director, CITA, University of Toronto
"Stellar Feedback and Galaxy Formation"

Star formation in galaxies is remarkably inefficient; naively one expects gas to cool rapidly,
and collapse to form stars on a dynamical time. But observations show that only two percent
of the gas in a galaxy is turned into stars per dynamical time. Similar comments apply to star
formation in individual giant molecular clouds. In the case of galaxies, current models attribute
the low efficiency to turbulence induced by energy input from supernovae. In giant molecular
clouds, the low efficiency is attributed to turbulent stirring by ionized gas (HII regions or shocked
stellar winds). I will argue that the low efficiency in both cases is driven primarily by radiation
pressure, from light produced by massive star clusters, on dust. I will present models that
reproduce the Carina and Westerlund I clusters in the Milky Way, the 20 or so massive clusters
in M82, and the even more massive clusters, with masses up to 100 million solar masses, that
dominate the dynamics of the ISM in ultraluminous galaxies like Arp 220. I will describe the
formation and evolution of such massive clusters, which should have a well defined mass-
radius relation and mass-to-light ratios that vary with cluster mass, and compare the results
to observations of massive clusters in the nearby universe.

Feb. 10th

David Pooley University of Wisconsin, Madison
"Zooming in on Dark Matter AND Quasar Accretion Disks
through Gravitational Lensing"

Under favorable conditions, the light from a distant quasar can be gravitationally lensed by
an intervening galaxy to produce four images of the quasar. I will present X-ray observations
of 14 such quasars recorded with the Chandra X-ray Observatory as well as corresponding
optical data obtained with either the Hubble Space Telescope or ground-based telescopes.
I will discuss an innovative technique of analyzing these quadruply-lensed quasars in optical
and X-ray emission that, for the first time, is able to resolve the structure of the accretion disk
around the black hole. The X-ray and optical observations together provide a micro-arcsecond
probe of the quasar, an angular resolution far beyond the reach of current and future telescopes.
I will also discuss how these same data are used to determine the amount of dark matter in
the lensing galaxy, as well as the mass-to-light ratio.

Feb. 17th

Mary Kay Hemenway
University of Texas at Austin
"International Year of Astronomy 2009"

The International Year of Astronomy 2009 is a global effort initiated by the International
Astronomical Union and UNESCO to help the citizens of the world rediscover their place
in the Universe. The year 2009 was especially chosen to commemorate the 400th anniversary
of the astronomical use of the telescope. with 136 nations participating, IYA2009 activities
are taking place locally, nationally, regionally and internationally. The hope is that by the end
of 2009 millions of people will have encountered astronomy in a new or exapanded manner
through 11 cornerstone projects, 9 special projects and 11 task groups. Several projects will
have long-term legacies. this presentation will review the efforts being done on the international,
national, state and local levels - and suggest ways in which you can participate.

Mar. 3rd

Brad Hansen
University of California, Los Angeles
"Modelling the White Dwarf Cooling Sequences of Globular Clusters"

I will describe the current state of ongoing efforts to model the white dwarf populations
of globular clusters, with an eye to constraining the age of the cluster using different
physics from the main sequence turnoff. This method has been tried on two clusters
(M4 and NGC6397) and is planned for a third (47 Tucanae). I will discuss the results
and remaining systematic limitations of this method.

Mar. 9th

Texas Cosmology Center Colloquium

Bhuvnesh Jain
University of Pennsylvania
"Testing Gravity with Gravitational Lensing and Dynamics"

Modifications of general relativity provide an alternative explanation to dark energy for
the observed acceleration of the universe. Modified gravity theories have richer observational
consequences for large-scale structure than conventional dark energy models -- for example,
how perturbations affect light rays and galaxy dynamics differs from general relativity. In this talk,
I will introduce gravitational lensing and its recent applications such as lensing tomography.
I will then discuss tests of gravity from kpc-Gpc scales using dynamics, lensing and redshift.

Mar. 10th

Donald Brownlee
University of Washington
"The Stardust Comet Sample Return Mission: New Insight into
the Origin of Comets and Crystalline Silicates in Disks"

Stardust, the NASA comet sample return mission, obtained thousands of small rocks from comet
Wild 2. Detailed laboratory study of this material from a body that formed beyond Neptune is
providing new insight into the origin of comets and crystalline silicates in circumstellar disks.
The comet contains abundant refractory materials that apparently formed in the inner solar system
and were transported to Kuiper belt. Large-scale radial transport processes carried familiar
components found in meteorites, like fragments of chondrules and Calcium Aluminum Inclusions,
to the edge of the solar system. The comet also contains ultra- refractory compounds that are
the first solids to condense from hot solar-composition gas. Pre-solar grains (stardust!) have been
found in the comet sample but their abundance appears to be lower than found in asteroidal
meteorites from the inner solar system. The new view of this Jupiter family comet is that it is a
remarkable mix of ices formed ~50K and inner solar system “rocky” materials that formed at

Mar. 11th

Special Physics Colloquium

Donald Brownlee
University of Washington
"Rare Earth?"

Our water-covered Earth is drastically different from other known planets. Earth's
surface water, land, friendly atmosphere, distance from the Sun, long term stability
and a host of other factors have provided an oasis in space that has nurtured microbial
life for billions of years and animal life for over 10% of Earth's history.

Earth is dramatically different from its neighboring planets, but how rare is it among
all planets? As we learn more about planets we are finding that they are a diverse
set of bodies with complex evolutionary histories. Is it easy to make Earths? How
Earth-like does a planet really have to be to support life like us? How long can
our planet support animals or even microbial life?

These and similar questions relate to our potential for detecting extraterrestrial life.
If life-supporting planets are too rare, they will be too far away for detailed study
or more fanciful endeavors.

Planets change over time and in the second half of its life, our Earth will become quite
"unearthly", an ocean-free body heated by an ever-brightening Sun. How long Earth's
plants and animals might survive in this period may depend on the actions and ingenuity
of a single species - humans.

Mar. 24th

Naoki Yoshida
University of Tokyo, IPMU
"Formation of Primordial Stars and Black Holes"

The first stars are thought to be the first sources of light, and also the first sources of heavy
elements. The first stars terminate the cosmic Dark Ages, set the scene for later galaxy
formation, and might also seed the formation of massive blackholes in the early universe.
I present the results from ultra-high resolution simulations of the formation of the first stars
within the framework of the standard cosmology. I show that tiny density fluctuations left over
from the Big Bang drive the formation of primordial protostars when the age of the universe
was less than a few million years. Our detailed calculations of proto-stellar evolution suggest
that the first stars are massive. Under some reasonable assumptions, some stars grow to be
more massive than 300 solarmasses, to collapse to black holes. I use another set of
cosmological simulations to answer to an important question, "Where are the first stars now?"
The simulations follow the formation of a Milky-Way size galaxy with an unprecedented
resolution, so that the old stellar remnants can be directly located within the galaxy's halo.
I propose a model that explains the apparent lack of pair-instability signature in metal-poor
halo stars. Finally, I will discuss prospects for future observations of the first stars and their
signatures exploiting ground-based and space-borne telescopes.

Apr. 7th




Jack W. Holt University of Texas at Austin, Institute for Geophysics
"Unraveling Icy Mysteries on Mars (and Earth) through Radar Sounding"

The composition and origin of several enigmatic features on Mars have been debated
for decades, ever since their discovery in Mariner 9 data. The prospect of ice within
large, lobate aprons surrounding massifs and abutting escarpments in the middle latitudes,
where ice is not stable at the surface, has intrigued geologists and inspired paleoclimate
modelers. In addition to the composition of the polar layered deposits, two major features
of the northern polar deposits have eluded explanation: the deep, spiral-shaped troughs
and the enormous Chasma Boreale which divides the polar cap into two major parts.
A series of missions using optical and other short-wavelength instruments have refined
the morphology and surface composition of all these features, yet a wide range of hypotheses
have persisted regarding their interior composition, formation, and relation to Mars climate
history. The advent of orbital radar sounding on Mars, with Mars Express and Mars
Reconnaissance Orbiter, has brought about a leap forward in our understanding of these
ice-related bodies, including composition, likely origin and evolution. The amount of known
water ice has increased dramatically. These advances would not have been possible
without decades of experience probing the depths of ice sheets on Earth with similar
techniques using aircraft-based instrumentation. I will describe how our work in Antarctica
has enabled these discoveries on Mars, present new radar data from Mars and explain
how studies on both planets are being used to solve icy mysteries in our solar system.

Apr. 14th

Michael R. Garcia Harvard-Smithsonian Center for Astrophysics
"The International X-Ray Observatory"

The International X-ray Observatory (IXO) promises to open a new window on the universe
by delivering on the promise of X-ray spectroscopy. Current observatories are able to obtain
high quality spectra on only the brightest x-ray sources. For the vast majority of x-ray sources
what pass for spectra are more akin to UBV colors. The IXO will allow routine spectroscopy
at R>1000 for typical sources, and provide a factor of 100 improvement in effective area
for high resolution x-ray spectroscopy. The science questions that the IXO will address
are very broad, and include: How do super-massive Black Holes grow and evolve?
Does matter orbiting close to a Black Hole event horizon follow the predictions of General
Relativity? What is the Equation of State of matter in Neutron Stars? How does Cosmic
Feedback work and influence galaxy formation? How does galaxy cluster evolution
constrain the nature of Dark Matter and Dark Energy? Where are the missing baryons
in the nearby Universe? When and how were the elements created and dispersed?
How do high energy processes affect planetary formation and habitability? How do
magnetic fields shape stellar exteriors and the surrounding environment? How are
particles accelerated to extreme energies producing shocks, jets, and cosmic rays?
The IXO is ready to compliment the suite of new large ground and space based
observatories coming in the next decade. This colloquium will discuss both the science
and the implementation of the IXO.

Apr. 27th

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 distance to the
host galaxy, based on a kinematic model.  We will explain the importance of
determining the Hubble Constant to 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 better than 3%.  Time permitting,
we will also present the scientific capabilities of the current and future NRAO facilities:
ALMA, EVLA, VLBA and GBT, for addressing key astrophysical problems.

May 5th

Beatrice M. Tinsley Visiting Scholar

Dan M. Watson University of Rochester, New York
"'Rainfall' from Protostellar Envelopes onto Protoplanetary Disks"

Class 0 protostars, the youngest type of young stellar objects, show many signs of rapid
development from their initial, spheroidal configurations. They are therefore studied
intensively for details of the formation and nature of the dense cores within protostellar
envelopes. At millimeter wavelengths, kinematic signatures of envelope collapse have
been observed in several such objects. These objects and many more Class 0s also
show evidence of strong high-velocity bipolar outflows. The long-sought link between
these two flows and the central protostar -- the embedded protoplanetary disk -- has
recently been discovered in observations with the Spitzer Space Telescope's Infrared
Spectrograph. We have detected rich emission spectra of water vapor, in the three most
abundant isotopologues, and hydroxyl, at wavelengths 20-37 microns, in a large fraction
of a sample of 110 face-on Class 0/I protostars. The observations indicate directly the
presence of extremely dense, warm gas from regions of Solar-system dimension. Models
based upon vigorous infall onto a disk, in the form of a plane-parallel disk-accretion shock,
reproduce the observed spectra well. In most cases the envelope-disk accretion rate
tracks the disk-protostar rate, but in others the former greatly exceeds the latter, as if
material is accumulating in the disk and the protostellar accretion rate will be violently
variable. More complex models are enabling precise constraints to be placed on the
structure and stability of the youngest protoplanetary disks. The observations also show
directly that water arrives in protoplanetary disks as a warm vapor rather than ice, thus
erasing any chemical signature of this material's interstellar origins.

May 19th

Beatrice M. Tinsley Visiting Scholar

Lisa Kaltenegger Harvard-Smithsonian Center for Astrophysics
"Frontiers in Extrasolar Planet Search - Toward the First Habitable Planets"

Detecting the first potentially Habitable Planet is just within our reach ... but how can we find
out if they are really habitable? In this talk we discuss how we can read a planet's spectrum to
assess its habitability. What can we look for in a spectral fingerprint of Earth and super-Earths
that can indicate life? We explore biomarkers on rocky exoplanets, explore geological epochs
on Earth, different biota and their effects, signs of different geochemical cycles, their detectability
and reliability. Ground as well as space-based telescopes to characterization of rocky exoplanets,
are already in the development phase (ELT, TNT, GMT, James Webb Space Telescope, Darwin,
TPF, NWO). We will assess their effectiveness and the best observation strategy to search
for the signature of a biosphere.

June 3rd

Christer Sandin Astrophysikalisches Institut Potsdam (AIP)
"Unfolding Properties of Mass Loss at the Tip of the Asymptotic Giant Branch"

In the final stages of stellar evolution low- to intermediate-mass stars lose their envelope in increasingly
massive stellar winds. Matter, which has been processed inside these stars, is thereby returned to
the interstellar medium, and mass loss also determines properties of subsequent planetary nebulae.
In order to obtain properties of winds at the tip of the asymptotic giant branch we observed weak halos
of a set of planetary nebulae in the galactic disk. For this purpose we used the method of integral field
spectroscopy together with a new dedicated data analysis method. In this presentation I will demonstrate
the key concepts of our method and also highlight our results. The data shows that mass loss rates
increase strongly in the final mass loss stage, and for several nebulae we derived a densely sampled
and steeply increasing temperature gradient into the halo - indicating that the halo is not in thermal

June 9th

Geza Kovacs Konkoly Observatory, Budapest
"Search for Transiting Planets: Methods, Results, Limitations and Prospects"

From the relatively long learning phase in periodic transit detection, the photometric method has
become the second contributor to planet discoveries after the more traditional radial velocity method.
With nearly 60 planets discovered by various photometric surveys, we focus on the most interesting
objects found by the HATNet project, spanning the mass range from super Neptunes to the
intermediate objects between Jupiter-mass planets and brown dwarfs. Special attention will be
paid to the method of detection and photometric trend filtering. The mounting difficulties in false
positive rejection for sub-Saturn objects will also be discussed.

Last Modified: June 8, 2009