1 research outputs found
Mass loss and very low-metallicity stars
Mass loss plays a dominant role in the evolution of massive stars at solar
metallicity. After discussing different mass loss mechanisms and their
metallicity dependence, we present the possibility of strong mass loss at very
low metallicity. Our models at Z=1e-8 show that stars more massive than about
60 solar masses may lose a significant fraction of their initial mass in the
red supergiant phase. This mass loss is due to the surface enrichment in CNO
elements via rotational and convective mixing. Our 85 solar mass model ends its
life as a fast rotating WO type Wolf-Rayet star. Therefore the models predict
the existence of type Ic SNe and long and soft GRBs at very low metallicities.
Such strong mass loss in the red supergiant phase or the Omega-Gamma limit
could prevent the most massive stars from ending as pair-creation supernovae.
The very low metallicity models calculated are also very interesting from the
nucleosynthesis point of view. Indeed, the wind of the massive star models can
reproduce the CNO abundances of the most metal-poor carbon-rich star known to
date, HE1327-2326. Finally, using chemical evolution models, we are able to
reproduce the evolution of CNO elements as observed in the normal extremely
metal poor stars.Comment: 8 pages, 3 figures, to appear in the proceedings of the conference on
"Unsolved Problems in Stellar Physics", Cambridge, 2-6 July 200