Oxygen-line formation in Population-II A-type stars

The non-LTE formation of neutral oxygen lines in the visible (lambda 6156-8) and near-IR (lambda 7771-5) region was studied, and extensive grids of theoretical non-LTE equivalent widths and abundance corrections were computed in the parameter range of -2 less than or equal to [Fe/H] less than or equal to 0,7000 K less than or equal to T-eff less than or equal to 14000 K, and 3.0 less than or equal to log g less than or equal to 4.0, with the intention of applying them to A-type stars, especially Population-II stars such as horizontal-branch objects. It was found that the inclusion of UV Lyman lines (such as Lyman beta overlapping with a strong OI resonance transition) in the background opacity may be important, which tends to suppress the non-LTE effect, especially for the metal-deficient case. Nevertheless, the resulting non-LTE correction for OI 7771-5 is still of considerable amount (greater than or similar to 0.5-1.0 dex), even in the weak-line cases of low abundance, and should inevitably be taken into account when determining oxygen abundance from this near-IR triplet.