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) and compare the yields with various abundance pattern of extremely metal-poor (EMP) stars. We assume that the observed EMP stars are the second generation stars, which have the metal-abundance pattern of the Pop III SNe. Previous theoretical yields and observations do not match well. In this paper we consider high energy explosions and mixing-fallback models. We show that the abundance patterns of both typical and C-rich EMP stars with [Fe/H] ∼ < −2.5 can be well reproduced with the yield of Pop III core-collapse SNe of M ∼ 20− 130M . The abundance patterns of the [Fe/H] ∼ < −2.5 stars correspond to supernova yields with normal explosion energies, while those of the carbon unenhanced stars with [Fe/H] ' −4 ∼ −3 correspond to high-energy supernova yields. The abundance pattern of C-rich ([C/Fe]∼ > 2) low [Fe/H] (' −5 ∼ −3.5) stars can be explained with the faint SN yield with little Ni ejection, which is similar to SN1997D. In the supernova-induced star formation model, we can qualitatively explain why the EMP stars formed by the faint or energetic supernovae have lower [Fe/H] than the EMP stars formed by normal supernovae. We also show that the absolute abundance of Fe-peak elements (Mn, Co, Ni, Zn) are sensitive to the electron mole fraction Ye during explosive nucleosynthesis. Even we vary Ye as a parameter, we still need a large explosion energy to obtain the large Co/Fe and Zn/Fe ratios observed in typical EMP stars with [Fe/H] ∼ < −3.5. Subject headings: Galaxy: halo — nuclear reactions, nucleosynthesis, abundances — stars: abundances — stars: Population III — supernovae: general — supernovae: individual (SN1997D)