Relics of the first generation supernovae in the extremely metal-poor stars

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  • 16 January 2003
Abstract
It is of vital importance in current astronomy to identify the first generation stars in the Universe, i.e., totally metal-free, population (Pop) III stars. Recent numerical models have shown that, the first stars are as massive as ~ 100Mo. The formation of long-lived low mass Pop III stars may be inefficient because of slow cooling of metal free gas cloud, which is consistent with the failure of previous attempts to find Pop III stars. Recently the most Fe-deficient and C-rich low mass star, HE0107-5240, was discovered. If this is a Pop III low mass star that has gained its metal from a companion star or interstellar matter, it could challenge the above theoretical models. Here we show that the abundance patterns of HE0107-5240 and other extremely metal poor (EMP) stars are in good accord with nucleosynthesis yields of supernova explosion of ~ 20-130Mo stars if the explosions undergo substantial mixing- fallback to form massive black holes. Such supernovae have actually been observed as faint supernovae. In contrast, the abundances of EMP stars are not consistent with nucleosynthesis in pair-instability supernovae from 130-300Mo stars. We propose that the first generation supernovae were mostly the explosion of ~ 20-130Mo stars and some of them produced Fe-poor but C, O-rich ejecta. From such ejecta, the second generation stars of small masses can be formed because of enhanced C, O cooling, even if the gases are extremely Fe-poor.

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