List of Past Astronomy Colloquia : 01-Sep-2003 to 31-Dec-2003

Date:   Wednesday 10-Sept-2003
Speaker:   Dr. Mark Whittle (University of Virginia)
Title:  Jet-Gas Interactions in Seyfert Galaxies

Collimated outflows are widespread phenomena in astrophysics, from stellar jets to radio quasars. When these outflows encounter the surrounding medium a number of phenomena can occur, including serious damage to both jet and medium. This talk presents a case study of such an interaction in a Seyfert galaxy, where strong emission lines provide important diagnotsic information to help unravel both the nature of the interaction and the nature of the jet.

Date:   Wednesday 17-Sept-2003
Speaker:   Dr. Amber Miller (Columbia University)
Title:  "Bumps, Wiggles, and Holes in the Sky - Exploring the Early Universe"

Date:   Wednesday 24-Sept-2003
Speaker:   Dr. Paul Feldman (Johns Hopkins University)
Title:  "A Spectroscopic Tour of the Solar System with the Far Ultraviolet Spectroscopic Explorer"

The spectral band, resolution, and sensitivity of the Far Ultraviolet Spectroscopic Explorer satellite, launched in June 1999, provide a unique capability to study the principal atoms, ions and molecules in a variety of planetary environments. The wavelength region from 905 to 1187 A, which is rich in emissions of H2 and CO as well as many ionic species, is observed at a spectral resolution of 0.3 A or less. This talk will describe recent observations and results on the atmospheres of Earth and Mars, polar aurora on Jupiter and Saturn, the Io plasma torus, and cometary comae.

Date:   Wednesday 01-Oct-2003
Speaker:   Dr. William Bottke, Southwest Research Institute
Title:  "The Dynamical Evolution of Asteroids and Meteoroids Via Yarkovsky Thermal Forces"

Over the last several decades, it has been assumed that collisions and gravitational forces are the primary mechanisms governing the evolution of asteroids and meteoroids. While models employing these processes can explain some aspects of the main belt and near-Earth asteroid (NEA) populations, they also make numerous predictions that are inconsistent with observations (e.g., meteorite cosmic-ray exposure ages that are an order of magnitude longer than standard models would predict, the peculiar orbital distributions of many asteroid families, the surprising number of km-sized asteroids with very fast or very slow rotation rates).

To resolve these discrepancies, we have invoked the Yarkovsky effect, a thermal radiation force that causes objects to undergo slow but steady semimajor axis drift and spin up/down as a function of their spin, orbit, and material properties. Numerical results suggest that this previous known but generally neglected mechanism can be used to: (i) deliver asteroids (and meteoroids) with diameter D < 20 km from their parent bodies in the main belt to chaotic resonance zones capable of transporting this material to Earth-crossing orbits, (ii) disperse asteroid families, with drifting bodies jumping or becoming trapped in mean-motion and secular resonances within the main belt, and (iii) modify the rotation rates of asteroids a few km in diameter or smaller. Based on our results, we believe that Yarkovsky thermal forces should now be considered as important as collisions and gravitational perturbations to our overall understanding of asteroid evolution.

Date:   Friday 03-Oct-2003 *** NOTE SPECIAL DATE ***
Speaker:   Dr. Andrew Blain (Caltech)
Title:  *** SPECIAL COLLOQUIUM *** "The History of Star Formation in Dusty Galaxies"

Much of the luminosity of galaxies over the Universe's history has been absorbed by interstellar dust and reprocessed to far-infrared wavelengths. I will describe the most luminous galaxies that are responsible for much of this emission, based on the results of ground-based surveys at submillimetre wavelengths. In particular, the key observational result on the redshift distribution of these galaxies, and the range of their spectral energy distributions, which is very important for observations with SIRTF.

Date:   Wednesday 08-Oct-2003
Speaker:   Dr. Cole Miller
Title:  "Black Hole Binaries, Gravitational Waves, and Cockroaches"

In the next decade, it is expected that instruments on Earth and in space will detect gravitational radiation from a variety of astrophysical sources. In addition to those that can be observed directly, however, there is a vastly larger number of sources that are individually undetectable, but whose collective effects might be evident in the noise spectra of gravitational wave instruments. I will discuss a new approach to the search for a background of these faint sources, based on variability of gravitational wave amplitude. This method has promise for revealing an otherwise difficult to detect population of black holes in dwarf galaxies, and may have implications for early universe structure formation.

Date:   Wednesday 15-Oct-2003
Speaker:   No colloquium

Date:   Wednesday 22-Oct-2003
Speaker:   Dr. James Bullock (Harvard-Smithsonian CfA)
Title:  "Cosmology and the Milky Way"

The standard scenario of cosmological structure formation is the Cold Dark Matter (CDM) paradigm. The theory is remarkably successful, especially when compared to large-scale data, although there are some potential difficulties on small scales. Within this picture, all galaxies are surrounded by gravitationally-dominant, extended, "halos" of dark matter, and the evolution of these dark mater halos govern the buildup of galaxies with time. A fundamental prediction of CDM is that all structure in the Universe forms hierarchically: small systems collapse first and fall together to form progressively larger systems over time. This talk focuses on testing this prediction against observations within our own Milky Way halo. Specifically, if the currently favored variant is right, then the Milky Way system should have accreted many tens of dwarf galaxies over its history, most of which were destroyed by tidal interactions. I present results from N-body simulations aimed at modeling this process, and show that the fossil remnants of tidally destroyed dwarf galaxies should be detectable as spatial structures in the outer stellar halo of the Milky Way. A detection of these features would be strong evidence that the dominant paradigm works well, even on small scales. A non-detection of substructure would be further evidence against CDM in the sub-galactic regime.

Date:   Wednesday 29-Oct-2003
Speaker:   Dr. Gillian Knapp (Princeton University)
Title:  "Brown Dwarfs"

Date:   TUESDAY 04-Nov-2003 *** Note special day; joint with Physics ***
Speaker:   Dr. Max Tegmark (UPenn/MIT)
Title:  "*** Note special date *** Cosmology with SDSS and WMAP"

I present the most accurate galaxy clustering measurements to date and discuss what we do and don't know about inflation, dark energy, dark matter and neutrinos from this, WMAP, gravitational lensing, the Lyman alpha forest and other cosmological probes. I outline my view of the most exciting challenges ahead.

Date:   Wednesday 12-Nov-2003
Speaker:   Dr. Richard Perley (National Radio Astronomy Observatory)
Title:  "The Expanded Very Large Array Project: Goals, Progress, and the Future for Radio Astronomy"

The Expanded Very Large Array project seeks to improve the capabilities of the VLA by at least an order of magnitude in all key observational capabilities: sensitivity, frequency coverage, spatial resolution, correlator capabilities, and imaging performance. The NRAO is now in the third year of funding the first phase of the project, and is now ready to submit to the NSF its proposal for funding the second, and final phase of the project.

In this talk, I will review the scientific and technical cases for both phases of the project: Phase I, which is primarily a comprehensive upgrade to the existing facility; and Phase II, which will expand the resolution of the array by an order of magnitude, extend wavelength coverage to below one meter, and enable wide-angle mosaicing at frequencies up to 50 GHz. When completed in ~2012, the EVLA will give astronomers unprecedented imaging capabilities for research into the properties of our evolving universe.

I will complete this review with a discussion of how the EVLA is an essential step to the next-generation radio telescope -- the Square Kilometer Array, and how development of the EVLA will benefit the SKA, LOFAR, and other proposed future radio facilities.

Date:   Wednesday 19-Nov-2003
Speaker:   Dr. Peter Goldreich (California Institute of Technology)
Title:  "Three Easy Pieces: Examples of Chaos in the Solar System"

I will introduce chaos by means of a pendulum. Then I will explain the role it plays in unpredictable orbits, in climate variations on Mars, and in the transport of meteorites from the asteroid belt to Earth. My presentation will include movies, demonstrations, and meteorites.

Date:   Wednesday 26-Nov-2003

Date:   Wednesday 3-Dec-2003
Speaker:   Dr. Virginia Trimble (UC Irvine/U Maryland)
Title:  "Review of Astrophysics in 2003"

Date:   Wednesday 10-Dec-2003
Speaker:   Dr. Margaret Meixner (Space Telescope Science Institute)
Title:  "The Evolution of Molecular Gas in Evolved Stars"

Intermediate mass stars (0.8-8 M_solar) end their lives with tremendous mass loss on the asymptotic giant branch (AGB). This mass loss strips the star's outer envelope rapidly revealing the hot core which is destined to be a white dwarf. The mass loss is predominantly molecular gas and dust and images of it tell us the history of the mass loss process. However, as the star passes through the proto-planetary nebula (PPN) phase and the core of the star is revealed, the molecular gas becomes photodissociated. When the core becomes hot enough to photoionize the envelope, the object becomes a planetary nebula (PN). I will present results from a BIMA survey of CO in evolved stars, which include AGB, PPN and PN objects. Some of the findings include mass-loss variation, and three different kinematic signatures. I will discuss the results in the context of the general literature of CO in evolved stars and of evidence for photodissociation, as opposed to shocks, dominating the evolution of the molecular gas envelope.

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