Statistics – Computation
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21715313s&link_type=abstract
American Astronomical Society, AAS Meeting #217, #153.13; Bulletin of the American Astronomical Society, Vol. 43, 2011
Statistics
Computation
1
Scientific paper
We present a chemical composition study of twenty-five stars in the metal-poor Galactic globular cluser M68. We obtained high-resolution spectra (R 40,000) in the wavelength region 3500-9000 A for the target stars with the the Magellan Inamori Kyocera Echelle (MIKE). The observed stars include 11 red giant branch (RGB) stars, 9 red horizontal branch (RHB) stars, and 5 blue horizontal branch (BHB) stars, which span an effective temperature range of approximately 5000K. The abundances were determined through equivalent width and synthetic spectrum analyses. The computations considered isotropic, coherent scattering in the continuum source functions. Sample stars from each group were analyzed using model atmospheres from the MARCS and ATLAS grids. We find a generally consistent metallicity across all the evolutionary groups: [Fe/H] = -2.4 (RMS deviation = 0.1). However, we note that the mean RHB metallicity is 0.15 dex less than the overall average. The relative abundance ratios of the alpha elements are typical for low metallicity stars: [Ca/Fe] = [Ti/Fe] +0.35, with only small variations among the RGB, RHB, and BHB stars. Star-to-star variations in proton-capture elements Na, O, and Al are apparent in the spectra. We will present representative abundances from other major element groups in all three stellar evolutionary domains.
Acknowledgements: we are grateful to NSF grant AST-0908978, the University of Texas John W. Cox Endowment for Advanced Studies in Astronomy, and the University of Texas Astronomy Department Rex G. Baker, Jr. Endowment for support of this project.
Preston George
Shectman Stephen
Simmons Sloane K.
Sneden Chistopher
Sobeck Jennifer
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