Jan 26

"Chemical Abundances of Stars in the Halo. II. New Extremely Metal-poor Stars"
Julie Krugler Hollek, University of Texas at Austin

We present new abundance results from the Chemical Abundances of Stars in the Halo (CASH) project. The ~500 CASH spectra were observed using the Hobby-Eberly Telescope in "snapshot" mode and are analyzed using an automated stellar parameter and abundance pipeline called CASHCODE. For the 20 most metal-poor stars of the CASH sample we have obtained high resolution spectra using the Magellan Telescope in order to test the uncertainties and systematic errors associated with the snapshot quality (i.e., R~15,000 and S/N~65) HET spectra and to calibrate the newly developed CASHCODE by making a detailed comparison between the stellar parameters and abundances determined from the high resolution and snapshot spectra. We find that the CASHCODE stellar parameters (effective temperature, surface gravity, metallicity, and microturbulence) agree well with the results of the manual analysis of the high resolution spectra. We present the abundances of three newly discovered stars with [Fe/H] < -3.5. For the entire pilot sample, we find typical halo abundance ratios with alpha-enhancement and Fe-peak depletion and a range of n-capture elements. The full CASH sample will be used to derive statistically robust abundance trends and frequencies (e.g. carbon and n-capture), as well as placing constraints on nucleosynthetic processes that occurred in the early universe.

Feb 2

"X-ray Spectroscopy of Hot White Dwarfs"
Jens Adamczak, University of Texas at Austin

I give an overview of the analysis of X-ray spectra of two hot white dwarfs observed by the Chandra satellite. Some DA white dwarfs show much smaller metallicities than predicted by the theory of radiative levitation. Many spectral lines of the heavy elements that are the key to the explanation to the unusual metal poorness are located in the X-ray wavelength range. Detailed analysis of X-ray spectra of single white dwarfs did not yet exist. The aim was to analyze spectra of the DA white dwarfs LB 1919 and GD 246 in different wavelength ranges in order to find out if the metals in the atmospheres of these objects are homogeneously mixed or chemically stratified. This helps to identify or exclude possible unexpected mechanisms that might disturb the equilibrium between gravitational and radiative forces in the atmosphere. The results show that the atmospheres of LB 1919 and GD 246 can be better reproduced by stratified model atmospheres. This indicates that the equilibrium between radiative levitation and gravitational settling is in good order and that the cause for the metal deficiency of LB1919 has to be found in an earlier evolutionary stage.

Feb 9

"Observational Constraints on Dark Matter Heating in White Dwarf Stars"
Mike Montgomery, University of Texas at Austin

We explore the observational consequences of the absorption and annihilation of dark matter particles as a source of heating in cool white dwarf stars (WDs). The heating prevents WDs in any population from cooling below a terminal luminosity, set by the local dark matter environment. This produces a potentially observable enhancement in the number of WDs near this luminosity. We discuss the limits set by current surveys and the possible improvements from future datasets.

Apr 6

"The KEPLER Mission: Programs, Opportunities, Data and Tools"
Karen Kinemuchi, Kepler Guest Observer Office/NASA Ames

OVERVIEW:
The Kepler Mission provides a wealth of astrophysical discoveries through the high precision monitoring of stars in 105 square degrees of sky located near the Cygnus-Lyra region. The database of ~170,000 light curves are revealing new planets, as well as new phenomena of the stars.

Dr. Karen Kinemuchi from the Kepler Guest Observer Office will be visiting the department next week on April 6 and 7 in order to discuss the Kepler mission and the opportunities for interested researchers. This provides an excellent opportunity for Kepler and Non-Kepler people alike to learn about the Kepler planetary and other astrophysics programs, opportunities, data and tools.

ABSTRACT:
The primary objective of the NASA Kepler mission is to find Earth-sized exoplanets in habitable zones. Kepler provides unprecedented high precision time-series photometry at either the long (30 minute) or short (1 minute) cadence. The Kepler Guest Observer Program supports the astronomical community on astrophysics research, ranging from eclipsing star systems, asteroseismology, dynamic eruptive or cataclysmic variable stars to active galactic nuclei. The Kepler data are being released to the public, and the Guest Observer Office is dedicated to supporting the community. This talk will focus on the science currently being done, but also some resources to help jump start future research.