AAS 201st Meeting, January, 2003
Session 17. Stellar Evolution and Metal-Poor Stars
Poster, Monday, January 6, 2003, 9:20am-6:30pm, Exhibit Hall AB

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[17.16] Determining Oxygen Abundances in Metal Poor Subdwarfs from Medium Resolution Spectra of the OI Triplet

C.R. James (Sam Houston State University), C.A. Pilachowski (NOAO, KPNO), T. Beers (Michigan State University), C. Sneden (The University of Texas at Austin), R.M. Cavallo (Lawrence Livermore National Laboratory)

In the determination of oxygen abundances in unevolved metal-poor stars, the OI triplet remains the most accessible feature, but is still quite weak in the most metal-poor (oldest) stars. Pilachowski & Armandroff (1996) have explored a technique to determine oxygen and iron abundances in faint evolved stars using low-dispersion spectroscopy of the oxygen triplet. At moderate resolution, the triplet lines are blended into a single feature that can be measured and analyzed as a spectroscopic blend. Because the lines are separated by only 3.4 , the blended feature is more easily detected than the individual features; thus reliable oxygen measurements can be made in much fainter stars. Also, the immediate vicinity of the oxygen triplet is free of atmospheric absorption line contamination, and the feature is unblended with other stellar lines from additional elements.

In this work, we have attempted to apply the Pilachowski and Armandroff (1996) methods to a sample of unevolved stars. Approximately half of the sample has been previously studied, allowing for a thorough assessment of the feasibility of applying the Pilachowski-Armandroff method to this population of stars. We find that the employing spectrum synthesis analysis to these low-dispersion spectra does sometimes yield meaningful results, and those results are consistent with high-resolution studies. However, in many cases, the weakness of the triplet allows for only determinations of upper limits, most of which are unenlightening. We explore the advantages and disadvantages of this method.

Support from NOAO and SHSU is gratefully acknowledged.

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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.