Astronomy Department Colloquia

Colloquia and PhD Talks Schedule Summer 2014

May 12 3 PM	Qualifying Exam/2nd Year Defense "Outflows and Chemical Enrichment from Clustered Supernovae in the First Galaxies" abstract Jeremy Ritter University of Texas at Austin Qualifying Exam Committee Meeting follows at 4 PM in RLM 15.216A
May 13 2 PM	Qualifying Exam/2nd Year Defense "The Lyman-alpha Signature of the First Galaxies" abstract Aaron Smith University of Texas at Austin Qualifying Exam Committee Meeting follows at 3 PM in RLM 15.216A
May 14 2 PM	Qualifying Exam/2nd Year Defense "Formation of Massive Star Clusters - an Application of Monte Carlo Radiation Hydrodynamics" abstract Tsz Ho (Benny) Tsang University of Texas at Austin Qualifying Exam Committee Meeting follows at 3 PM in RLM 15.202A
May 22 3:30 PM	Special Seminar "Fragmentation in Primordial Gas: Improving H2 Cooling and Self-Shielding" abstract Tilman Hartwig University of Heidelberg, Germany (host: Volker Bromm)
June 10 3 PM	Special Visiting Speaker Presentation (visiting: 7-14 June 2014) "Pre-supernova Convection in Massive Stars" abstract Manos Chatzopoulos University of Chicago host: Crag Wheeler
July 10 11 AM	PhD Defense Presentation "Creating and Measuring White Dwarf Photospheres in a Terrestrial Laboratory" As the ultimate fate of nearly all stars, including our Sun, white dwarfs (WDs) hold rich and informative histories in their observable light. To determine a fundamental parameter of WDs, mass, we perform the first measurement of the average gravitational redshift of an ensemble of WDs. We find a larger mean mass than that determined from the primary and expansive technique known as the spectroscopic method. The potential inaccuracy of this method has broad astrophysical implications, including for our understanding of Type 1a supernova progenitors and for constraining the age of the Universe. This motivates us to investigate the WD atmosphere models used with the spectroscopic method, particularly the input theoretical line profiles, by developing a new experimental platform to create plasmas at WD photospheric conditions (T_e~1 eV, n_e~10^17 cm^-3). Instead of observing WD spectra to infer the plasma conditions at the surface of the star, we set the conditions and measure the emergent spectra in the laboratory. X-rays from a z-pinch dynamic hohlraum generated at the Z Pulsed Power Facility at Sandia National Laboratories irradiate a gas cell to initiate formation of a large (120x20x10 mm or 24 cm^3) plasma. We observe multiple Balmer lines from our plasma in emission and in absorption simultaneously along relatively long (~120 mm) lines of sight perpendicular to the heating radiation. Using a large, radiation-driven plasma aides us to achieve homogeneity along our observed lines of sight. With time-resolved spectroscopy we measure lines at a range of electron densities that spans an order of magnitude, and we do this within one pulsed power shot experiment. Observing our plasma in absorption not only provides the signal-to-noise to measure relative line shapes, it allows us to measure relative line strengths because the lines share the same lower level population. This constrains the theoretical reduction factors used to describe ionization potential depression or the occupation probability associated with these Balmer lines. We compare our measured line shapes with the theoretical ones used in WD atmosphere models as part of the first fruits of this rich experimental platform. close Ross Falcon University of Texas at Austin PhD Committee Meeting follows at 12 Noon in RLM 15.216A
July 10 3 PM	PhD Defense Presentation "Study of Galactic Clumps with Millimeter/Submillimeter Continuum and Molecular Emission: Early Stages of Massive Star Formation" abstract Manuel Merello University of Texas at Austin PhD Committee Meeting follows at 4 PM in RLM 15.216A
July 11 11 AM	PhD Defense Presentation "Simulating the Formation, Properties, and Impact of Stellar Systems in the First Galaxies" abstract Chalence Safranek-Shrader University of Texas at Austin PhD Committee Meeting follows at 12 Noon in RLM 15.216A
Aug 8 2 PM	Special Presentation "The Violent Early Lives of Stars and Planets" abstract Joel Green University of Texas at Austin
Aug 11 11 AM	PhD Defense Presentation "The Chemical Abundances of Stars in the Halo" Julie Hollek University of Texas at Austin PhD Committee Meeting follows at 12 Noon in RLM 15.202A
Aug 14 2 PM	PhD Defense Presentation "Radiation Hydrodynamics and Simulations of Astrophysical Phenomena" Chris Lindner University of Texas at Austin PhD Committee Meeting follows at 4 PM in RLM 15.202A