List of Past Astronomy Colloquia : 01-Sep-2005 to 31-Dec-2005

Date:   Wednesday 05-Oct-2005
Speaker:   Dr. Scott Ransom (NRAO)
Title:  "Hittin' the Pulsar Jackpot in Globular Cluster Terzan 5"

Terzan 5 is a dense globular cluster near the Galactic center that has been predicted for >15 years to contain tens or even hundreds of millisecond pulsars (MSPs). Observations of MSPs in globular clusters provide unique probes into an astonishingly wide variety of science including relativity tests, stellar evolution, cluster dynamics, plasma physics, and black holes. But deep searches with some of the world's best radio telescopes had only managed to uncover 3 pulsars over the same period of time. This past year, observations at 2GHz with the Green Bank Telescope significantly changed all that with the discovery of (at least) 28 new MSPs, most of which are in binary systems. Several of these binaries are truly unique and/or exotic systems, and two them provide strong evidence for the existence of "massive" neutron stars (>1.6 Msun). In this talk I'll discuss the reasons behind the project, the observation itself, and some of the implications of the new discoveries.

Date:   Wednesday 12-Oct-2005
Speaker:   Dr. Craig Heinke (Northwestern)
Title:  "X-ray Binaries in the Globular Cluster Terzan 5"

The globular cluster Terzan 5 is one of the densest globular clusters in the Milky Way, with one of the highest predicted rates of encounters between stars in its core. These predictions have been borne out by the identification within Terzan 5 of a low-mass X-ray binary (LMXB) and dozens of radio pulsars . Two Chandra observations have clearly identified the quiescent counterpart of the LMXB, and dozens of additional X-ray sources. Terzan 5 is a heavily obscured cluster, lying behind >10^22 atoms cm^{-2} of obscuring gas and dust. I will talk about what we can learn about the X-ray sources in Terzan 5, despite this obscuring curtain, and by comparison, about the faint X-ray sources in the Galactic Center.

Date:   Wednesday 19-Oct-2005
Speaker:   Dr. Margaret Turnbull (DTM, CIW)
Title:  "TBD"

Date:   Wednesday 26-Oct-2005
Speaker:   Dr. Andy Rivkin (APL, JHU)
Title:  "Water and OH on Asteroids: What (we think) we know, and what (we're pretty sure) we don't"

Although asteroids tend to be thought of as rocky rather than icy bodies, many contain water or hydroxyl bound in minerals. The observations that have been made sometimes confirm what was expected, but have also been surprising, and helped change recent paradigms. I will present results for objects large and small, and also touch upon expected future directions.

Date:   Wednesday 02-Nov-2005
Speaker:   Prof. Heather Morrison (Case Western Reserve University)
Title:  The "Ring Around the Galaxy" -- outer disk or star stream?

There have been several recent claims for new satellites of the Milky Way located close to the edge of its disk. These include the Monceros stream, the "Ring around the Galaxy" and the Canis Major dwarf. High reddening, crowding and the galactic warp make it difficult to study this region of the Galaxy. I will present recent spectroscopy from a multi-faceted study of the Milky Way halo (the Spaghetti survey). Our results call into question the identification of these structures toward the edge of the Milky Way disk with debris from accretions of dwarf satellites. Our velocity data (and that of Yanny et al 2003) show that these detections are consistent with a simpler explanation: a flared outer disk caused by interaction with a still undiscovered dwarf which heated the outer disk.

Date:   Wednesday 09-Nov-2005
Speaker:   Prof. Govind Menon (Troy University)
Title:  "Energy Extraction from Rotating Black Holes"

Following a brief introduction to 3+1 Electrodynamics in curved space-time, the nature of the constraint equation that arises in the study of a force free, axis-symmetric, stationary magnetosphere will be discussed. The relevance of the streaming function Omega and the nature of poloidal surfaces will be developed from a geometric point of view. Finally we shall present an analytic solution to the constraint equation and discuss its physical properties.

Date:   Wednesday 16-Nov-2005
Speaker:   Dr. Marc Kuchner (GSFC)
Title:  "Reading the Resonant Signatures of Planets in Debris Disks"

A planet in a circumstellar dust cloud can carve an easily visible signature in the dust density via orbital resonances. This pattern can point to the planet and reveal its orbit even when the planet itself is much too faint to see. I will paint an overview of the variety of resonant structures a single planet can create in an optically thin dust disk, taking a theoretical perspective. I'll discuss observations of debris disks with Spitzer, JWST, ALMA, Keck and TPF.

Date:   Wednesday 30-Nov-2005
Speaker:   Dr. Rob Olling (U. Maryland)
Title:  "The Milky Way: A Connection between Stars, Galaxies and the Universe"

Date:   Wednesday 07-Dec-2005
Speaker:   Dr. Risa Wechsler (Chicago)
Title:  "Lighting up the Dark: Connecting Galaxies to Mass"

Many of the most vital questions in cosmology require a detailed understanding of a simple question: How does mass connect to light? Making this connection, often described by the galaxy "bias", is essential both to use galaxy clustering to constrain cosmological models and the nature of dark energy, and to develop a physical understanding of the origin of galaxy properties and their correlations. I will describe several advances towards making this connection, which combine the results of numerical simulations with observations of galaxy clustering and of galaxy clusters. I will describe results from a simple yet accurate model which connects dark matter subhalos to galaxies, and is able to reproduce nonlinear galaxy clustering as a function of luminosity from z~5 to the present. This indicates that gravity and dynamical evolution of the dark matter halos are the main factors responsible for the spatial distribution of galaxies. I will then discuss the validity of a central assumption often used to connect galaxies to halos: that their clustering properties depend only on the mass of their hosts. Finally, I will describe a method of connecting galaxies to the mass distribution which is applicable to very large volume simulations, and show how it can be used in combination with large cluster surveys to pin down cosmological parameters and the nature of dark energy.

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