Oxygen abundance determination of B-type stars with the O i 7771–5 Å lines

Abstract

Abstract Oxygen abundances of 34 B-type stars in the effective temperature range of Teff ∼ 10000–28000 K with diversified rotational velocities (vesin i ∼ 0–250 km s−1) were determined from the O i triplet lines at 7771–5 Å, with an aim of examining whether this O i feature can be a reliable abundance indicator for such high-temperature stars including rapid rotators. It revealed that the required non-local thermodynamic equilibrium (LTE) abundance correction is distinctly large (ranging from ∼−0.6 dex to ∼−1.7 dex) and its consideration is indispensable. On the condition that the non-LTE effect is taken into account, this triplet is a useful O abundance indicator (with a precision of ≲ 0.2 dex) up to Teff ≲ 25000 K, since its total equivalent width is sufficiently large ( ≳ 200 mÅ). In contrast, it is not adequate for abundance derivation for stars at Teff ≳ 25000 K, where its strength rapidly drops down toward a hardly detectable level (except for sharp-lined stars) and its sensitivity to Teff or log g becomes considerably large. The resulting non-LTE oxygen abundances turned out to be almost normal (i.e., near-solar around ∼8.7–8.8 within ∼±0.2 dex) for most stars without any dependence upon projected rotational velocity as well as luminosity (or mass), which is consistent with the prediction of recent stellar evolution calculations.