Oxygen abundances in two metal-poor subgiants from the analysis of the 6300 angstrom forbidden OI line

Recent LTE analyses (Israelian et al.; Boesgaard et al.) of the OH bands in the optical ultraviolet spectra of nearby metal-poor subdwarfs indicate th at oxygen abundances are generally higher than those previously determined from the analysis of the [O I] doublet in the spectra of low-metallicity gi ants. On average, the difference increases with decreasing metallicity and reaches Delta[O/Fe] similar to +0.6 dex as [Fe/H] approaches -3.0. Employin g high-resolution (R = 50,000), high-signal-to-noise ratio (similar to 250) echelle spectra of the two stars found by Israelian et al. to have the hig hest [O/Fe] ratios, viz., BD +23 degrees 3130 and ED + 37 degrees 1458, we conducted abundance analyses based on about 60 Fe I and seven-nine Fe II li nes. We determined from Kurucz LTE models the appropriate values of T-eff, log g, [Fe/H], and v(t), as well as abundances of Na, Ni, and the tradition al alpha-elements Mg, Si, Ca, and Ti, independent of the calibration of col or versus T-eff scales. We determined oxygen abundances from spectral synth esis of the stronger line (lambda 6300) of the [O I] doublet. The ionizatio n equilibrium of Fe indicates that these two stars are subgiants rather tha n subdwarfs, and our derived values of T-eff are 150-300 K lower than those assumed by the previous investigators, although the resulting [Fe/H] value s differ only slightly. The syntheses of the [O I] line lead to smaller val ues of [O/Fe], consistent with those found earlier among halo field and glo bular cluster giants. We obtain [O/Fe] = +0.35 +/- 0.2 for BD +23 degrees 3 130 and + 0.50 +/- 0.2 for BD + 37 degrees 1458. In the former, the [O I] l ine is very weak (similar to 1 m Angstrom), so that the quoted [O/Fe] value may in reality be an upper limit. Therefore, in these two stars a discrepa ncy exists between the [O/Fe] ratios derived from [O I] and the OH feature, and the origin of this difference remains unclear. Until the matter is cla rified, we suggest it is premature to conclude that the ab initio oxygen ab undances of old, metal-poor stars need to be revised drastically upward.