|Fall 2004 Astronomy Colloquia - University of Texas at Austin|
August 31, 2004
University of Arizona
"Origins of Stellar Masses: The IMF from the Solar Neighborhood to the Local Group"
The origin of the initial mass function of stars and substellar objects remains one of the
outstanding problems in astronomy. Its solution would provide constraints on the mass-to-light
ratio of integrated stellar populations, clues concerning the formation and evolution of the Milky
Way, and point toward a predictive theory of star formation. Work over the past decade suggests
that the stellar IMF is not a sensitive function of metallicity or star-forming environment. New
observational techniques, exploiting advances in infrared instrumentation on large ground and
space-based telescopes, have enabled more stringent tests of the hypothesis: is the IMF
universal? We describe current efforts to extend studies of the IMF into the brown dwarf regime
as well to extreme regions of star formation in our galaxy and other members of the local group.
Finally, we introduce a novel approach to constraining the ratio of high to low mass stars in very
young "super star clusters" found in starburst galaxies.
September 7, 2004
University of Texas at Austin, Dept. of Physics
"High Energy Density Science with Intense Lasers
and its Potential Application to Astrophysics"
September 14, 2004
Jacqueline N. Hewitt
Director, MIT Center for Space Research
"Toward Observations of Neutral Hydrogen Structures During the Epoch of Reionization"
September 21, 2004
University of Texas at Austin<
"The Age of the Universe, Extreme Physics, Distant Solar Systems,
and Other Wisdom from the White Dwarf Stars"
October 5, 2004
University of California San Diego
"Numerical Simulations of the Sunyaev-Seldovich in Galaxy Clusters"
The SZ effect in galaxy clusters is emerging as a powerful probe of cosmological
structure formation. Large surveys are planned in coming years to observe the epoch of
galaxy cluster formation and thereby constrain the dark energy equation of state.
The success of these efforts rely on the ability to connect the observables -- the SZ decrement
(or increment) -- to cluster mass. In this talk I report on recent numerical simulations of cluster
formation and evolution which establish this connection. It is found that a tight correlation
exists which bodes well for upcoming surveys.
October 1, 2004
University of Arizona
"A New View of the Magellanic Clouds"
I will describe a photometric survey of the Large and Small Magellanic Clouds and
results obtained so far from those data. In particular, I will focus on some lessons
learned regarding our interpretation of the internal extinction and morphology of external
galaxies, and on the drivers of star formation on galactic scales. With regard to the latter issue,
I will present evidence for multiple bursts of star formation in the SMC and describe how
interactions with the Milky Way may be responsible.
October 19, 2004
"Testing Star-Formation Theory and Setting the Clock for Planet Formation:
Empirical Calibration of Pre-Main-Sequence Stellar Evolution Models"
Our ability to observationally determine the timescales involved in protoplanetary disk
evolution---accretion, dissipation, planet formation---depends on our ability to determine
accurate ages for the young stars that host these disks. But ages for young stars are assigned
on the basis of pre-main-sequence stellar evolution models that have yet to be empirically
calibrated with respect to stellar age and mass. Lacking a good chronometer for young stars,
systematic uncertainties limit our knowledge of the timescale for planet formation. Systematic
uncertainties in masses for young stars similarly limit our understanding of the nature of the
stellar initial mass function (IMF), particularly for lowest-mass young stars and brown dwarfs.
We review the current pre-main-sequence stellar models, discuss uncertainties in the masses
and ages they predict, and describe an ongoing observational program to test and refine
their empirical calibration.
October 26, 2004
University of Arizona
"Dark Energy and Cosmic Sound"
The acoustic oscillations of the photon-baryon fluid in the early universe
imprints a signature of known scale into the clustering of matter and
galaxies at recent times. Large galaxy redshift surveys can recover
this scale as a set of oscillations in the power spectrum, thereby
measuring the Hubble parameter and angular diameter distance relation
as a function of redshift. Such cosmological measurements could permit
precise and robust constraints on the dark energy equation of state.
I will describe the prospects for detecting and utilizing the acoustic
oscillations within current and future galaxy surveys.
November 2, 2004
University of Texas at Austin, Dept. of Physics
"Patterns, Craters, and Shocks in Granular Media"
Granular media such as sand, cereal, pills, and interstellar dust grains are less well
understood than fluids and solids. We test theoretical predictions for granular dynamics
in laboratory experiments on vertically oscillating granular layers. The experiments
reveal stripe, square, hexagonal, spiral, and localized patterns, depending on the
container oscillation frequency and amplitude. In granular flows, shock waves are
common since the speed of sound (pressure waves) is typically only a few centimeters/second.
Lab experiments on the impact of projectiles yield craters similar to those formed by meteorites
on the earth or the moon; the dynamics are surprising. Particle simulations using Newton's
laws and continuum fluid simulations provide insight into the laboratory observations.
November 9, 2004
"Observing Black Holes with 1m Telescopes"
Over the past 6 years, we have been engaged in an extensive program of optical/IR observations
of transient X-ray binary systems. Dynamical mass measurements show that many of these
systems contain compact objects with masses greater than the upper limit for neutron stars -
these systems are sometimes referred to as "Dynamically Confirmed Black Hole Candidates"
(DCBHCs). Detailed study of accretion flows onto DCBHCs holds the promise of identifying
and studying strong-field relativistic effects. But these flows are complex, and require
multiwavelength observations to constrain their properties. Curiously, the X-ray data, acquired
at great expense, are often more complete than the O/IR data, which can be obtained with
small ground-based telescopes. The need to acquire appropriate O/IR data is one of the
principal science goals of the Small and Moderate Aperture Research Telescope System (SMARTS).
In this talk, I will discuss both the organization and capabilities of SMARTS, and recent scientific
results on DCBHBs.
November 16, 2004
"Structure Formation in the Early Universe"
I present the results from recent large cosmological simulations of early structure formation
I show how the first cosmic structure emerges from small density perturbations in the early
universe. The first stars light up the universe, ionize and heat the intergalactic medium and
pollute it with heavy elements early on, setting an initial condition for the first galaxy formation.
I will discuss the formation and evolution of the early cosmological HII regions and subsequent
cooling and condensation of the primordial gas in detail.
November 23, 2004
University of Texas at Austin
"Secular Evolution and the Growth of Pseudobulges in Disk Galaxies"
This talk is an updated summary of Kormendy and Kennicutt 2004, ARAA, 42, 603.
I review internal processes of slow ("secular") evolution in galaxy disks, concentrating
on the buildup of dense central features that look like classical, merger-built bulges but that
were made slowly out of disk gas. These are called pseudobulges. As an existence proof,
I first review how bars rearrange disk gas into outer rings, inner rings, and gas dumped
into the center. In simulations, this gas reaches high densities that plausibly feed star formation.
In the observations, many barred and oval galaxies show central concentrations of gas and star
formation. Star formation rates imply plausible pseudobulge growth times of a few billion years.
If secular processes built dense central components that masquerade as bulges,
can we distinguish them from merger-built bulges? Observations show that pseudobulges
retain a memory of their disky origin. They have one or more characteristics of disks:
(1) flatter shapes than those of classical bulges, (2) large ratios of ordered to random
velocities indicative of disk dynamics, (3) small velocity dispersions, (4) spiral structure or
nuclear bars in the bulge part of the light profile, (5) nearly exponential brightness profiles,
and (6) starbursts. These structures occur preferentially in barred and oval galaxies in which
secular evolution should be rapid. So the cleanest examples of pseudobulges are recognizable.
Thus a large variety of observational and theoretical results contribute to a new picture of galaxy
evolution that complements hierarchical clustering and merging. Much of the richness in galaxy
structure that is embodied in de Vaucouleurs' and Sandage's morphological classification
schemes is now reasonably well understood.
November 30, 2004
Anglo Australian Observatory
"Unravelling the Epoch of Dissipation in the Early Galaxy"
Galactic archaelogy: fossil information preserved in the stars. We are entering a new era
where it is possible to obtain dynamical and chemical information on millions of stars with
the same observing apparatus. Unravelling the dissipative processes which lead to the
disk present a major challenge which we discuss. Some of the dynamical information must
preserve important clues about early galactic history. We review what are the likely signatures
and what these may tell us about the sequence of events which lead to the formation of the
Galaxy. Some of the weaker signatures will only become evident from uniform phase space
information for millions of stars.
A highly resolved spectrum of a cool star reveals a rich forest of absorption lines arising from 60
or more chemical elements. The relative strengths of these lines reflect the physical conditions in
the progenitor cloud, processes involved in stellar evolution, interactions with other stars and
the ISM, and the surface physics of the star. The limited success of atmospheric codes indicates
that we are at an early stage in our understanding of stellar chemistry. For all galaxy components,
there must be a great deal of fossil information locked up in these complex chemical signatures,
which we review.