List of Past Astronomy Colloquia : 01-Jan-2006 to 01-Jun-2006

Date:   Wednesday 08-February-2006
Speaker:   Dr. Rachel Osten (U. of Maryland)
Title:  "Yes, Virginia, There Really is Magnetic Activity in Brown Dwarf and Ultracool Stars"

Date:   Wednesday 15-February-2006
Speaker:   Dr. Andrew Harris (U. of Maryland)
Title:  "Steps to Exploring the High-redshift Molecular Universe"

Date:   Wednesday 22-February-2006
Speaker:   Dr. Craig Agnor (U. of California-Santa Cruz)
Title:  "The Capture Origin of Triton"

Date:   Wednesday 1-March-2006
Speaker:   *** CANCELLED ***

Date:   Wednesday 08-March-2006
Speaker:   Dr. Tracy Clarke (Naval Research Laboratory)
Title:  "Probing Clusters of Galaxies at Radio and X-ray Wavelengths"

Date:   Wednesday 15-March-2006
Speaker:   Dr. Gordon Stacey (Cornell University)
Title:  "Submillimeter Spectroscopy of Distant Galaxies"

Date:   Wednesday 22-March-2006

Date:   Wednesday 29-March-2006
Speaker:   Dr. Jay Lockman (National Radio Astronomy Observatory)
Title:  "Galactic Hydrogen from the Disk to the Halo: Recent Observations with the Green Bank Telescope"

Date:   Wednesday 05-April-2006
Speaker:   Dr. Joe Burns (Cornell University)
Title:  "Cassini Views Saturn's Rings: Our Local Astrophysical Lab"

Date:   Wednesday 12-April-2006
Speaker:   Dr. Tod Strohmayer (NASA Goddard Space Flight Center)
Title:  "Taking the Measure of Neutron Stars: Recent efforts to Probe Fundamental Physics"

Date:   Wednesday 19-April-2006
Speaker:   Dr. Mark Krumholz (Princeton University)
Title:  "Turbulence, Feedback, and Slow Star Formation"

One of the outstanding puzzles about star formation is why it proceeds so slowly. Structures ranging from giant molecular clouds in the Milky Way to entire starburst galaxies convert only a few percent of their gas into stars per dynamical time. I present a model that quantitatively explains low star formation rates as the result of supersonic turbulence in virialized star-forming gas. The turbulence in turn is driven by star formation feedback, which injects energy to offset radiation from isothermal shocks. This model is able to reproduce, and in several cases successfully predicted, observational results covering a wide range of scales, including the star formation rate in dense molecular clumps and infrared dark clouds, the age spreads of young star clusters, the lifetimes and column densities of giant molecular clouds, the total amount and radial distribution of star formation in the Milky Way, the Kennicutt Law, and the extragalactic infrared-HCN correlation. The model makes additional quantitative predictions that will be testable in the next few years.

Date:   Wednesday 26-April-2006
Speaker:   Dr. Priya Natarajan (Yale University)
Title:  "Probing the Nature of Dark Matter Using Gravitational Lensing

Gravitational lensing has been used to constrain the details of mass distributions on a range of scales. Within dense cluster environments we present the results of a technique that utilizes galaxy-galaxy lensing and provides more interesting clues to the nature of dark matter and its equation of state. I will also present comparison of lensing inferred dark matter properties with those of simulated clusters from the Millennium Run.

Date:   Wednesday 03-May-2006
Speaker:   Dr. Michael A'Hearn (U. of Maryland) -- CMPS Lecture Series
Title:  "Deep Impact: What We Learned About Comets"

Date:   Wednesday 10-May-2006
Speaker:   Dr. Luis Aguilar (UNAM)
Title:  "The Case of the Missing Binaries"

We compare the frequency of field binary stars as a function of Galactic velocity and find a deficiency of such stars in strongly retrograde orbits. Metal-poor stars moving on prograde Galactic orbits have a binary frequency of 28.3%, whereas the retrograde stars' binary frequency is only 10.2% for V<-300 km/s.

No such defficiency is seen as a function of U or W velocities, nor for [Fe/H]. We explore possible mechanisms that may explain the observed defficiency.

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