Abstract

KLAPP, J et al. Nucleosynthesis constraints on the First Stars. Rev. mex. fis. [online]. 2006, vol.52, suppl.1, pp.50-56. ISSN 0035-001X.

Star formation and accretion calculations have recently suggested that the first stars are composed of Very Massive Stars (VMS). On the other hand, very massive supernovae (SN) explosion calculations have suggested that the VMS hypothesis is inconsistent with abundance determinations in Extremely Metal Poor (EMP) stars. As an alternative scenario, we propose that the first stars are born very massive but their mass reduced to the Massive Star (MS) range during their hydrogen and helium burning phases. In this paper we present some details of Zero Age Main Sequence (ZAMS) models and evolutionary calculations of a mass losing 5OOM Pop III star. The results indicate that VMS have very high effective temperatures, a large ratio of radiation to total pressure and a luminosity close to the Eddington luminosity and hence, we expect them to have significant radiation driven winds. For conservative evolution our evolutionary tracks are similar to those found in the literature but with the introduction of mass loss the evolution changes strongly and we have shown that VMS can reduce its mass to the MS range if the mass loss parameter N is equal or greater than ~ 300. We have estimated the total amount of matter ejected through winds until the end of the helium burning phase. The proposed scenario suggests that the first stars are born VMS but transformed into MS during their hydrogen and helium burning phases, end as black holes or hypernovae producing the Fe-rich and r-poor abundances observed in EMP stars, and that could be connected to low redshift gamma-ray bursts and the reionization of the Universe.

Keywords : Stellar evolution; first stars; population III stars; mass loss.

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