Chemical enrichments by massive stars and the effects of rotation

All model output of massive star evolution, i.e, the paths in the HR diagra m, the lifetimes, the surface and wind composition, the chemical yields and the nature of the progenitors of supernovae strongly depend on both mass l oss and rotation. We examine here specifically the effects of mass loss and rotation on the chemical yields of CNO elements. A major effect is that th e importance of mass loss depends: on the metallicity Z of the galaxies. Th is may also be the case for stellar rotation in massive stars, in the sense that average rotation may be faster at lower metallicities. (C) 2000 Elsev ier Science B.V. All rights reserved.