Stellar Evolution at Low Metallicity

Raphael Hirschi$^1$, Cristina Chiappini$^{2,3}$, Georges Meynet$^2$, Andr'e Maeder$^2$, & Sylvia Ekstr"om$^2$

$^1$Keele University, UK
$^2$Observatoire de Gen`eve, CH
$^3$Osservatorio Astronomico di Trieste, Italia

Massive stars played a key role in the early evolution of the Universe. They formed
with the first halos and started the re-ionisation. It is therefore very important
to understand their evolution. In this review, we first recall the effect of
metallicity (Z) on the evolution of massive stars. We then describe the strong impact of
rotation induced mixing and mass loss at very low $Z$. The strong mixing leads to a
significant production of primary N14, C13 and Ne22. Mass loss
during the red supergiant stage allows the production of Wolf-Rayet stars, type Ib,c
supernovae and possibly gamma-ray bursts (GRBs) down to almost $Z=0$ for stars more massive than
60 $M_odot$. Galactic chemical evolution models calculated with models of rotating
stars better reproduce the early evolution of N/O, C/O and C12/C13.
Finally, the impact of magnetic fields is discussed in the context of GRBs.

Reference: "Massive Stars as Cosmic Engines" Conference proceedings, F. Bresolin, P.A. Crowther, J. Puls Eds
Status: Conference proceedings


Comments: 12 pages, 7 figures