Mixing of CNO-cycled matter in massive stars
Dr. Karl Remeis-Observatory & ECAP, Sternwartstr.7, D-96049 Bamberg, Germany
Dr. Karl Remeis-Observatory & ECAP, Sternwartstr.7, D-96049 Bamberg, Germany
Max-Planck-Institute for Astrophysics, Karl-Schwarzschild-Str. 1, D-85741 Garching, Germany
Geneva Observatory, University of Geneva, Maillettes 51, CH-1290 Sauverny, Switzerland
Geneva Observatory, University of Geneva, Maillettes 51, CH-1290 Sauverny, Switzerland
Abstract
Anomalies in the light element abundances in massive stars on the main sequence and more pronounced in their evolved stages are known since long. These are explained by evolution models for rotating stars as the consequence of mixing of nuclear-processed matter into the stellar atmosphere. However, recent analyses of large star samples have challenged the concept of rotational mixing. We report on the abundances of helium, carbon, nitrogen and oxygen in a sample of Galactic massive stars covering the main sequence to the blue supergiant stage in the mass range ~9 to 25Mo. High-quality spectra are homogeneously analysed throughout the optical to near-IR using improved NLTE line-formation and comprehensive analysis strategies. Extremely tight trends among the light element abundances are found for the first time, tracing the nuclear paths of the CNO-cycles quantitatively. The improved observational constraints will facilitate model predictions to be tested in unprecedented detail and they may guide future improvements to the models.