Department of Astronomy Colloquia Schedule for Fall 2010
University of Texas at Austin

Aug. 31, 2010

Mansi Kasliwal, California Institute of Technology (Caltech)
"Needles in the Haystack: Discovering Transients in the Gap between
Novae and Supernovae"

For the past several decades, there has existed a glaring six-magnitude luminosity gap between
the brightest novae and faintest supernovae. To find optical transients that are fainter and faster
than supernovae and rarer than novae, we designed a systematic search - "Palomar Transient Factory".
Theorists predict a variety of mechanisms to produce transients in the gap and observers have the
best chance of finding them in the local universe. Here I will present discoveries and unique physics
of cosmic explosions that bridge this gap between novae and supernovae. This effort works towards
building a complete inventory of transients in the local universe (d < 200 Mpc). It better prepares us
for the search of potential electromagnetic counterparts to the emerging fields of gravitational wave,
neutrinos, UHECR and TeV astronomy.

Sep. 07, 2010

Hilke Schlichting, Canadian Institute for Theoretical Astrophysics
"Collisions in the Kuiper Belt: The missing link between the Kuiper Belt
and other debris disks"

The Kuiper belt is a remnant of the primordial Solar system and provides valuable insights into planet
formation processes. It consists of a disk of icy bodies located beyond the orbit of Neptune. The size
distribution of Kuiper Belt objects contains many important clues concerning their formation, their
effective strength and their collisional evolution. I will present our latest results from our HST survey
which probes the size distribution of small Kuiper belt objects and their collisional evolution. In addition,
I will discuss the recent discovery of the first collisional family in the Kuiper belt and its formation.

Sep. 14, 2010

Bonnie Buratti, Jet Propulsion Laboratory
"Seasons in the Outer Solar System"

The planets and moons in the outer Solar System exhibit seasons just as the Earth does,
and for the same reason: they are tilted with respect to the sun-planetary plane. The outermost
bodies - Pluto and Triton - exhibit the transport of frost over decades instead of years. Careful
photometric observations, many gathered by students, have detected seasonal volatile movement
on Triton and possibly Pluto. The sublimated volatiles are nitrogen and methane rather than water
as on the Earth. The Cassini mission to Saturn is closely scrutinizing Titan, the large almost
Earth-like moon of Saturn, to detect seasonal formation of clouds and ethane lakes on its surface.

Sep. 21, 2010

Milos Milosalvjevic, University of Texas at Austin, Astronomy Dept.
"Growing Massive Black Holes at Cosmic Dawn"

Massive black holes inhabit the centers of all but the smallest of galaxies. Billion solar mass black
holes were present when the universe was at a tenth of its present age. How did such extreme objects
emerge on the cosmic stage? Attempting to trace their evolution to the beginnings quickly leads to
formidable theoretical challenges. Black holes produced in the standard stellar core collapse
face particular obstacles to becoming massive. A head start in the prompt formation of a black hole
already more massive than any star would have interesting theoretical and observational implications.
I will discuss the radiatively-efficient and radiatively-inefficient avenues for the subsequent growth,
and for the latter, I will attempt to gain insight from the empirically rich physics of the cosmic gamma-ray
burst sources. Ultimately, however, a growing black hole competes with star formation in the host galaxy.
It is thus worthwhile to study the structure and formation of dwarf galaxy nuclei. In the nearby universe
they do not seem to contain massive black holes, but in the early universe dwarf galaxy nuclei should
have been sites of massive black hole formation.

Sep. 28, 2010

Naveen Reddy, National Optical Astronomy Observatory (NOAO)
"Evolution of Dust Obscuration and Its Implications for Galaxy Growth"

I will review recent work to constrain the star formation history of the Universe based on UV measurements,
and will discuss what we have learned about the dust properties of typical star-forming galaxies at high redshift.
In particular, I will briefly summarize our results on the UV luminosity function at redshifts z~2-3; the steep
faint-end slope at these redshifts has interesting implications for the shape of the galaxy stellar mass function
and budget of total stellar mass at high redshift. I will focus on how dust obscuration evolves with bolometric
and UV luminosity, redshift, stellar population age, and metallicity. I show that evolution in the luminosity function
and dust obscuration significantly impacts our understanding of the cosmic star formation history and its
reconciliation with the buildup of stellar mass at early epochs.

Oct. 05, 2010

Lam Hui, Columbia University
"Equivalence Principle and Cosmic Acceleration"

Recent attempts to modify gravity at long distances to explain cosmic acceleration generally introduce new
degrees of freedom, for instance a scalar, that must be screened in the solar system to satisfy stringent
experimental constraints. We will discuss how such screening mechanisms might lead to order unity
equivalence principle violations - in suitable environments - namely, objects with different degrees of
screening fall at different rates. Proposals to observe such effects, or rule out such theories, will be
discussed. We will also discuss screening mechanisms that are robust against this kind of equivalence
principle violation.

Oct. 12, 2010

Ellyn Baines, Naval Research Laboratory
"Interferometry: What is it and what can it do?"

Astronomers are applying the interference of light to study stars in ways not possible by any other means.
The CHARA Array and NPOI Interferometers reveal features on and around stars that remain mere pinpoints
of light even in the most powerful telescopes. I will describe what interferometry is and how it is used as well
as many of the exciting astronomical findings emerging from each instrument.

Oct. 19, 2010

Evan Kirby, California Institute of Technology (Caltech)
"The Chemical Evolution of Milky Way Satellite Galaxies"

The dwarf spheroidal (dSph) satellite galaxies of the Milky Way make good subjects for testing chemical
evolution models because they contain many stars bright enough for medium-resolution spectroscopy
and because they span a wide range of velocity dispersion and luminosity. I will present the results of
a Keck/DEIMOS spectroscopic campaign of eight Milky Way dSphs. The primary data product is a catalog
of nearly 3000 stars with spectral synthesis-based abundance measurements of Fe and the alpha elements
Mg, Si, Ca, and Ti. Maximum likelihood fits of analytic chemical evolution models to the eight metallicity
distributions show that the histories of the less luminous dSphs were marked by massive amounts of
gas loss, whereas the more luminous galaxies accreted gas during their star formation lifetimes.
The average [alpha/Fe] ratios for all dSphs follow roughly the same path with increasing metallicity.
There is little evidence of the predicted knees in the [alpha/Fe] vs. [Fe/H] diagram, corresponding to
the metallicity at which Type Ia supernovae begin to explode. Instead, Type Ia supernova ejecta
contribute to the abundances of all but the most metal-poor ([Fe/H] < -2.5) stars. Finally, I will show
the results of a numerical chemical evolution model that tracks elemental abundance patterns, star
formation rate, Types II and Ia supernova explosions, and supernova feedback. Similar to the analytic
models, the numerical models reveal that the star formation history of a dSph is a strong function
of its present-day luminosity.

Oct. 26, 2010

Elaine S. Oran, University of Michigan & Naval Research Laboratory
"Studies in Turbulent Combustion: Implications for Type Ia Supernovae"

The development and evolution of turbulent burning fronts are critical components in all natural,
deliberate, or accidental high-speed combustion scenarios. This includes, for example, Type Ia
thermonuclear supernovae (SNIa), engines for high-speed flight, and accidental catastrophes
surrounding fuel storage plants (such as Buncefield, UK) and coal mines (such as SAGO, WV).
In the most general picture, the combustion process starts from a weak spark or small flame,
evolves to a turbulent flame that subsequently grows in intensity and speed, and might undergo
a transition to a detonation. In this presentation, we first show the physics of the combustion
process through descriptions of experiments, accident investigations, and direct numerical
simulations. Then we will focus on an underpinning physical question of how a flame interacts
with a turbulent background field. Through the course of this discussion, we will indicate how
general properties of flames and detonation can apply to SNIa explosions, and how we can
use them to address the question of the origin of the transition to detonation in SNIa.

Nov. 02, 2010

Tadeusz Patzek, University of Texas at Austin, Dept. of Petroleum and Geosystems
"Global Energy Demand and Peak Oil"

In my seminar, I will discuss the scale of energy demand in the U.S. and world. I will comment
on the global peaks of oil and coal production, and their implications for the integrated global
economy. I will use the Gulf of Mexico as an example of a high production rate, high decline rate
oil and gas province. I will comment on the reasons for the aggressive offshore exploration
and production programs. Finally, I will describe the major reasons for the failure of BP's
Macondo well, and its impact on the future of oil and gas production in the Gulf.

Nov. 5, 2010: Friday

Eduard Vorobiev, St. Mary's University, Nova Scotia, Canada
"Embedded Protostellar Disks Around (sub-)Solar Stars:
The Dark Ages of Disk Evolution and the Planet Formation Perspective"

(Sub-)solar-type stars form via gravitational collapse of rotating molecular hydrogen cores
and planets emerge in gaseous and dusty disks that form around stars during the collapse.
I will discuss the earliest stages of the evolution of star+disk systems when they are deeply
embedded in parent cloud cores. Embedded disks are difficult to probe with modern
telescopes due to obscuration of light, yet this phase may be crucial for the subsequent
evolution. To study these elusive phases of disk evolution, I employ numerical hydrodynamic
simulations that start from a starless cloud core and terminate when the core has accreted
onto a forming star+disk system. I show that the path along which a star+disk object moves
is largely determined by the initial properties of the parent cloud core. Objects formed from
low-angular-momentum and low-mass cores proceed along a rather calm path showing
a low-amplitude accretion (and luminosity) variability caused by mild disk instability.
On the contrary, objects formed from high-angular-momentum and high-mass cores
exhibit high- amplitude variability, disk pulsations, and disk fragmentation. Most of the
forming fragments are quickly driven into the disk inner regions and (likely) onto the star,
triggering intense luminosity outbursts. If dust sedimentation in the fragments is fast enough,
some of them may survive the rapid inward migration and form icy giants or even terrestrial
planet cores on close orbits. A small fraction of the fragments may form gas giants and settle
on wide orbits around the central star, resembling in appearance the Fomalhaut b or HR 8977.

Nov. 09, 2010

Thomas Henning, Max Planck Institut fur Astronomie
"The Cold Universe - Star Formation with the Herschel Observatory"

The successful launch of the Herschel Observatory opened a new window for the
investigation of the cold universe. In the talk I will concentrate on the early science results
of Herschel in the field of star formation. Among these results is the detection of cold
filamentary structures, the observational evidence for a new class of very deeply embedded
protostars and the characterization of the mass function of cores. The examples will serve
as an illustration of the amazing research opportunities provided by Herschel.

Nov. 16, 2010

Philip Hopkins, University of California, Berkeley
"How do Massive Black Holes Get their Gas (and Get Rid of It)?"

Recent observations of tight correlations between supermassive black hole masses and
the properties of their host galaxies demonstrate that black holes and bulges are co-eval,
and have motivated theoretical models in which feedback from AGN activity regulates the
black hole and host galaxy evolution. I'll review the state of models and observations
regarding quasar and AGN fueling and feedback, using new multi-scale simulations
that can probe from galaxy scales down to the accretion disk. Combining simulations,
analytic models, and recent observations, answers to a number of questions are starting
to take shape: How to AGN get triggered? How long do they live? Are there relics in the
local Universe -- perhaps even in M31 and the Milky Way -- that provide unique information
on the epoch of black hole growth? Is feedback necessary/sufficient to regulate BH growth?
What effects does that feedback have on the host galaxy? And how does this interact with
the dynamics of stellar evolution and other sources of feedback in the ISM?

Nov. 23, 2010

Duane Liedahl, Lawrence Livermore National Laboratory
"X-ray Photoionized Plasmas in Space and in the Laboratory"

Recent advances in experimental capabilities have opened up the possibility of creating
laboratory plasmas for which continuum X-ray radiation dominates the heating, ionization,
and spectral response. The environments of black holes and neutron stars constitute
two examples in Nature where the high-energy radiation energy density is dominant.
I discuss some of the issues related to making the connection between laboratory plasmas
and astrophysical plasmas, and provide a description of plans for a series of experiments
using the Sandia Z Machine and the National Ignition Facility.

Nov. 30, 2010

Nitya Kallivayalil, Massachusetts Institute of Technology
"Towards the Study of the Milky Way in 6-D"

Tidal Streams provide a powerful probe of the potential of the Milky Way halo over large
Galactocentric distances and their detailed phase-space structure potentially gives us clues
as to the nature of dark matter. Powerful theoretical techniques are now available to re-construct
the underlying potential from the six-dimensional phase-space parameters that describe stellar
tracers. Notably absent from the presently available data-sets are full 3-D velocities. I will
describe ongoing efforts to remedy this aimed at tracers that sample the Milky Way halo at
a large range of distances: from the stellar halo to the Magellanic Clouds. Our Magellanic
Clouds results in particular were unexpected. I will also describe efforts to expand the
number of reference QSOs suitable for space-based astrometry, and what we ultimately
hope to learn about halo shape and distribution.

Last Modified: January 2010