Chemical enrichment by Wolf--Rayet and asymptotic giant branch stars

Abstract

We present theoretical models of Wolf-Rayet (WR) stars for two different sets of mass-loss rates. We compare with observed properties of WR stars and discuss implications for the enrichment of the interstellar medium in both cases. Sets of stellar yields for these stars together with corresponding yields from new models of asymptotic giant branch (AGB) stars are presented and discussed. We find carbon enrichment from WR stars to be on a level comparable to or greater than that from AGB stars for most scenarios. The models predict well the surface abundances and number ratios of WR stars but a population of binaries is needed if the models are to reproduce simultaneously both the observed mass-loss rates and positions on the Hertzsprung-Russell diagram.