Oxygen abundance determination of B-type stars with the OI 7771-5A lines

TL;DR

This study assesses the reliability of the OI 7771-5A triplet as an oxygen abundance indicator in B-type stars, emphasizing the importance of non-LTE corrections for accurate measurements across a wide temperature range.

Contribution

It demonstrates that the OI triplet can be a reliable oxygen abundance indicator in B-type stars up to 25000K when non-LTE effects are properly corrected, expanding its applicability.

Findings

Non-LTE corrections are large (~-0.6 to -1.7 dex) and essential for accurate abundance determination.

The triplet provides precise oxygen abundances (<~0.2 dex) for stars with Teff <~25000K.

Oxygen abundances are near-solar and show no dependence on rotational velocity or luminosity.

Abstract

Oxygen abundances of 34 B-type stars in the effective temperature range of Teff~10000-28000K with diversified rotational velocities (vesini~ 0-250km/s) were determined from the OI triplet lines at 7771-5A, with an aim to examine whether this OI feature can be a reliable abundance indicator for such high-temperature stars including rapid rotators. It revealed that the required non-LTE abundance correction is distinctly large (ranging from ~-0.6dex to ~-1.7dex) 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 <~0.2dex) up to Teff <~25000K, since its total equivalent width is sufficiently large (>~200mA). In contrast, it is not adequate for abundance derivation for stars at Teff >~25000K, 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 +/-~0.2dex) 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.