Effects of stellar winds and rotation on the evolution of massive stars

Abstract

We discuss the impact of the inclusionof both mass loss and rotation in massive star models at different metallicities.Rotation much improves the agreement between theory and observation. In particular rotational mixing allows to produce variations of the surface abundances already during the Main-Sequence phase. The changes of the surface abundances are more important when, for a given initial velocity, the initial mass increases, and/or the initial metallicity decreases. Alsothe observed high number of red supergiants at low metallicity can be accounted for by rotating stellar models, as well asthe observed variation of the number ratioof Wolf-Rayet to O-type stars as a function of the metallicity and the variation with themetallicity of the number ratio of type Ibc to type IIsupernovae. In all these questionsnon-rotating models give unsatisfactory fits. Rotating models can also give interestinginsights on questions as the origin of the Be stars, themechanisms responsible for thehuge mass loss rates undergone by the Luminous Blue Variables, the sources of primary nitrogen at low metallicity, the rotation rateof pulsars and the progenitors of the collapsars.