Oxygen Abundances in Metal‐poor Stars (−2.2 < [Fe/H] < −1.2) from Infrared OH Lines

Infrared OH lines at 1.55 - 1.56 um in the H-band were obtained with thePhoenix high-resolution spectrograph at the 2.1m telescope of the Kitt PeakNational Observatory for a sample of 14 metal-poor stars. Detailed analyses ofthe sample stars have been carried out, deriving stellar parameters based ontwo methods: (a) spectroscopic parameters; (b) IRFM effective temperatures,trigonometric gravities and metallicities from Fe II lines. The Fe I linespresent in the H-band region observed showed to be well fitted by the stellarparameters within $\Delta$[Fe/H] < 0.15 dex. The oxygen abundances were derivedfrom fits of spectrum synthesis calculations to the infrared OH lines. CO linesin the H- and K-bands were obtained for a subsample in order to determine theircarbon abundances. Adopting the spectroscopic parameters a mean oxygen-to-ironratio of [O/Fe] ~ +0.52 is obtained, whereas using the IRFM temperatures,Hipparcos gravities and [FeII/H], [O/Fe] ~ +0.25 is found. A mean of the twomethods gives a final value of [O/Fe] ~ +0.4 for the metallicity range -2.2 <[Fe/H] < -1.2 of the sample metal-poor stars.Comment: Astrophysical Journal, in press (scheduled for the v556 n2 Aug 1, 2001 issue