Variations in the Abundance Pattern of Extremely Metal‐Poor Stars and Nucleosynthesis in Population III Supernovae

We calculate nucleosynthesis in Population (Pop) III supernovae (SNe) andcompare the yields with various abundance patterns of extremely metal-poor(EMP) stars. We assume that the observed EMP stars are the second generationstars, which have the metal-abundance patterns of Pop III SNe. Previoustheoretical yields of Pop III SNe cannot explain the trends in the abundanceratios among iron-peak elements (Mn, Co, Ni, Zn)/Fe as well as the large C/Feratio observed in certain EMP stars with [Fe/H] <~ -2.5. In the present paper,we show that if we introduce higher explosion energies and mixing-fallback inthe core-collapse SN models of M ~ 20 - 130 Msun, the above abundance featuresof both typical and C-rich EMP stars can be much better explained. We suggestthat the abundance patterns of the [Fe/H] ~ -2.5 stars correspond to supernovayields with normal explosion energies, while those of the carbon un-enhanced([C/Fe] < 1) stars with [Fe/H] =~ -4 ~ - 3 correspond to high-energy supernovayields. The abundance patterns of the C-rich ([C/Fe]>~ 2) and low [Fe/H] (=~ -5\~ -3.5) stars can be explained with the yields of faint SNe that eject little56Ni as observed in SN1997D. In the supernova-induced star formation model, wecan qualitatively explain why the EMP stars formed by the faint or energeticsupernovae have lower [Fe/H] than the EMP stars formed by normal supernovae. Wealso examine how the abundance ratios among iron-peak elements depend on theelectron mole fraction Ye, and conclude that a large explosion energy is stillneeded to realize the large Co/Fe and Zn/Fe ratios observed in typical EMPstars with [Fe/H] <~ -3.5.Comment: 33 pages, 17 figures, 7 tables, To appear in the Astrophysical Journal 2005, January 1