2000A&A...359.1085P

An extensive model atom for non-LTE line formation calculations for OI is presented, taking into account recent improvements in the atomic data. Based on line-blanketed LTE model atmospheres equivalent widths are computed in LTE and non-LTE for the diagnostic OI lines of A- and late B-type stars in the range T_eff=7500K to 15000K and luminosity classes V to Ia. Non-LTE abundance corrections are provided: they span a wide range in magnitude, from less than 0.1dex for the weak lines in main sequence stars to more than 1.5dex for the near-infrared lines in some supergiants. The dependence of the non-LTE effects on the atmospheric parameters is discussed with special emphasis on supergiants. In particular, the near-infrared transitions are found to react sensitively to the collisional excitation cross sections used in the calculations. Further investigations concentrate on the influence of microturbulence and on the role of wind outflow velocity fields on the line formation. As a test and first application of the model, oxygen abundances for Vega (A0V), η Leo (A0Ib) and HD 92207 (A0Iae) are derived. The analysis of Vega confirms a slight oxygen underabundance (∼0.3dex) in this star while η Leo and HD 92207 show a nearly solar value. For Vega the observed spectrum can be reproduced accurately by the calculated line profiles. In supergiants consistent abundances can be derived from the weak lines in the visible. At high luminosities the prominent near-infrared features - among other strong lines from different elemental species - are subject to additional broadening by an unidentified process which prevents an equally accurate theoretical interpretation.