Program: GS-2004A-Q-20

Title:Comparative Chemical Evolution in Stellar Populations: Infrared Spectroscopy of Galactic Bulge Red Giants
PI:Verne V Smith
Co-I(s): Donald Terndrup, Katia Cunha, Nicholas B Suntzeff

Abstract

High-resolution, high-quality infrared spectroscopy of red giant stars in the Galactic bulge is now possible. Chemical abundances derived from such stellar spectra can be used to study chemical evolution in a distinctive environment within the Milky Way. Two important elements whose abundances are especially amenable to analysis via infrared spectroscopy are oxygen and fluorine, observable as OH and HF vibration-rotation lines in the infrared. Oxygen abundances, when combined with those from iron, provide information on the average star formation rate over time. Fluorine abundances are a unique tracer of the quantitative yields from neutrino spallation nucleosynthesis that occurs during supernova core collapse: this exotic nuclear process may play an important role in chemical evolution. We will determine the O/Fe and F/O abundance ratios in a sample of 6 red giant stars, spanning a range in metallicity and belonging to the bulge population. This work will result in the most accurate determinations of oxygen versus iron in the bulge, as well as the first fluorine abundances. Both of the prime targeted species, O and F, probe the output from massive stars that explode as supernovae of Type II. The abundance ratios derived here will allow us to compare the rate of chemical evolution in the bulge to other populations in the Milky Way, such as the disk and the halo.

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