Variations in the abundance pattern of extremely metal-poor stars and nucleosynthesis in Population III supernovae

We calculate nucleosynthesis in Population III supernovae (SNe) and compare the yields with various abundance patterns of extremely metal-poor (EMP) stars. We assume that the observed EMP stars are second-generation stars, which have the metal-abundance patterns of Population III SNe. Previous theoretical yields of Population III SNe cannot explain the trends in the abundance ratios among Fe-peak elements (Mn, Co, Ni, Zn)/Fe or the large C/Fe ratio observed in certain EMP stars with [Fe/H] less than or similar to -2.5. In this paper we show that if we introduce higher explosion energies and mixing fallback in the core-collapse SN models of M similar to 20-130 M-., the above abundance features of both typical and C-rich EMP stars can be much better explained. We suggest that the abundance patterns of the [Fe/H] similar to -2.5 stars correspond to supernova yields with normal explosion energies, while those of the carbon unenhanced ([C/Fe] < 1) stars with [Fe/H] similar or equal to -4 to -3 correspond to high-energy supernova yields. The abundance patterns of the C-rich ([C/Fe] greater than or similar to 2) and low [Fe/H] (similar or equal to 5.5 similar to -3.5) stars can be explained with the yields of faint SNe that eject little Ni-56 as observed in SN 1997D. 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 examine how the abundance ratios among Fe-peak elements depend on the electron mole fraction Y-e and conclude that a large explosion energy is still needed to realize the large Co/Fe and Zn/Fe ratios observed in typical EMP stars with [Fe/H] less than or similar to -3.5.