OXYGEN ABUNDANCES IN METAL-POOR SUBGIANT STARS FROM THE O-I-TRIPLET

This paper examines the oxygen abundance of 24 main-sequence turn-off- and subgiant stars through the permitted O I triplet near lambda 7774 Angstrom. In agreement with prior investigators, we find that the O ab undance from the triplet is about 0.53 dex higher than is typically fo und from other means such as the [O I] lambda 6300 Angstrom Line or th e UV and LR bands from OH. Our average [O/Fe] is +0.79+/-0.29 (1 sigma ), with the uncertainties in the individual methods being dominated by systematic errors in our incomplete understanding of the formation of these high-excitation lines under non-LTE conditions. Several methods of resolving the ongoing discrepancy are discussed in detail. We find that the problem is not fixed by simply changing the model. atmospher e parameters, and that the best methods seem to require a detailed non -LTE analysis based on both the structure of the oxygen atom and the s ource function within and above the photosphere. The trend of increasi ng O with decreasing Fe is briefly explored and is found to be qualita tively consistent with other works.