Constraints on rotational mixing from surface evolution of light elements in massive stars

Abstract

Context. Light elements and nitrogen surface abundances together can constrain the mixing efficiencies in massive stars on the main sequence, because moderate mixing in the surface layers leads to depletion of light elements but only later to enrichment in nitrogen. Aims. We want to test the rotational mixing prescriptions included in the Geneva stellar evolution code (GENEC) by following the evolution of surface abundances of light isotopes in massive stars. Methods. The GENEC is a 1D code containing sophisticated prescriptions for rotational mixing. We implemented an extended reaction network into this code including the light elements Li, Be, and B, which allowed us to perform calculations testing the rotation-induced mixing. Results. We followed 9, 12, and 15 M-circle dot models with rotation from the zero age main sequence up to the end of He burning. The calculations show the expected behaviour with faster depletion of light isotopes for faster rotating stars and more massive stars. Conclusions. We find that the mixing prescriptions used in the present rotating models for massive single stars can account for most of the observations; however, the uncertainties are quite large, making it hard to draw a firm conclusion on the mixing scenario.