Mass loss and very low-metallicity stars

TL;DR

This paper explores how massive stars at extremely low metallicity can experience significant mass loss due to surface enrichment, affecting their evolution, supernova types, and nucleosynthesis, with implications for early universe observations.

Contribution

It demonstrates that very low-metallicity massive stars can undergo strong mass loss, influencing their end states and nucleosynthesis, which was previously uncertain at such low metallicities.

Findings

Stars >60 solar masses can lose significant mass in the red supergiant phase.

Models predict the formation of type Ic supernovae and long-soft GRBs at low metallicity.

Wind models match observed CNO abundances in extremely metal-poor stars.

Abstract

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.