Massive star evolution at high metallicity

After a review of the many effects of metallicity on the evolution of rotating and non-rotating stars, we discuss the consequences of a high metallicity on massive star populations and on stellar nucleosynthesis. The most striking effect of high metallicity is to enhance the amount of mass lost by stellar winds. Typically at a metallicity $Z=0.001$ only 9% of the total mass returned by non-rotating massive stars is ejected by winds (91% by supernovae explosion), while at solar metallicity this fraction may amount to more than 40%. High metallicity favors the formation of Wolf-Rayet stars and of type Ib supernovae. It however disfavors the occurrence of type Ic supernovae. We estimate empirical yields of carbon based on the observed population of WC stars in the solar neighborhood, and obtain that WC stars eject between 0.2 and 0.4% of the mass initially locked into stars under the form of new synthesized carbon. Models give values well in agreement with these empirical yields. Chemical evolution models indicate that such carbon yields may have important impacts on the abundance of carbon at high metallicity.