On some properties of very metal-rich stars

An analysis of some properties of stellar models as a function of metallicity Z (and helium content Y ) is presented, with special attention to those stars with metallicities higher than twice or three times solar. It is shown that the stellar properties as a function of Z are mainly determined by the effects of the opacities at sub- solar metallicities, and by the effects of the mean molecular weight and stellar mass loss at higher metallicities. As a result, very metal-rich stars (Z > 0:05) exhibit properties that deviate from what is expected from the known characteristics at lower metallicities. In particular, they are more luminous and hotter than those at Z < 0:05 due to the effect of the mean molecular weight. They have main sequence lifetimes much shorter (60% shorter at Z =0 :1 than at Z =0 :02) than those at solar metallic- ity due to their lower initial hydrogen content. Finally, the high mass loss rates at high metallicities affect significantly the pop- ulation synthesis of massive stars in very metal-rich regions. An analysis of expected Wolf-Rayet and supernovae populations in such conditions is briefly presented.