Non-LTE line-formation for CNO

Abstract

Accurate atomic data have become available in the recent past due to the demands of astrophysics and fusion research. We report on the impact of such data on non-LTE line-formation calculations for CNO in early-type stars. Considerable improvement is achieved by the derivation of consistent results from practically all available spectroscopic indicators, regardless of ionization stage or spin system, and the uncertainties in the analyses are drastically reduced. Moreover, systematic trends are revealed, e.g. an increase of the NI abundances from previous studies of BA-type supergiants by a factor of two is indicated. The present work promises stringent observational constraints on chemical mixing in the course of massive star evolution. First results on BA-type supergiants in the Galaxy and the Magellanic Clouds are discussed.