Evolution and fate of very massive stars

Abstract

There is observational evidence that supports the existence of Very Massive\nStars in the local universe. First, very massive stars (Mini<=320 M) have been\nobserved in the Large Magellanic Cloud . Second, there are observed SNe that\nbear the characteristics of Pair Creation Supernovae which have very massive\nstars as progenitors. The most promising candidate to date is SN2007bi. In\norder to investigate the evolution and fate of nearby very massive stars, we\ncalculated a new grid of models for such objects, for solar, LMC and SMC\nmetallicities, which covers the initial mass range from 120 to 500M. Both\nrotating and non-rotating models were calculated using the Geneva stellar\nevolution code and evolved until at least the end of helium burning and for\nmost models until oxygen burning. Since very massive stars have very large\nconvective cores during the Main-Sequence phase, their evolution is not so much\naffected by rotational mixing, but more by mass loss through stellar winds.\nTheir evolution is never far from a homogeneous evolution even without\nrotational mixing. All the VMS, at all the metallicities studied here, end\ntheir life as WC(WO) type stars. At solar metallicity, none of our models is\nexpected to explode as a PCSN. At the metallicity of the LMC, only stars more\nmassive than 300 M are expected to explode as PCSNe. At the SMC metallicity,\nthe mass range for the PCSN progenitors is much larger and comprises stars with\ninitial masses between about 100 and 290 M . All VMS stars in the metallicity\nrange studied here produce either a type Ib or a type Ic SN. We estimate that\nthe progenitor of SN2007bi, assuming a SMC metallicity, had an initial mass\nbetween 160 and 175 M . None of models presented in this grid produce GRBs or\nmagnetars. They lose too much angular momentum by mass loss or avoid the\nformation of a BH by producing a completely disruptive PCSN.\n