Nucleosynthesis in Population III Stars and Chemical Abundances of Extremely Metal-Poor Stars

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The first generation of stars, called Population III stars, in the Universe do not contain heavy elements. In this study, we tried to investigate their nature from the comparison between nucleosynthesis and the chemical abundances of extremely metal-poor (EMP) stars. We focus on the peculiar abundance pattern of EMP stars. For example, (Mn, Cr)/Fe decrease while (Zn, Co)/Fe increase toward smaller metallicity. Such an abundance pattern may stem from nucleosynthesis in Pop III stars.In the first year of this study, we calculated the evolution and explosions of Pop III stars for a wide range of stellar masses and explosion energies and found interesting features of their nucleosynthesis In the second year, we extended our study to the aspherical explosion models. Our findings are summarized as follows:1)We found that nucleosynthesis in Hypernova explosions can explain the above abundance patterns of EMP stars.2)Pair instability supernovae in 130-300 M_【of sun】 stars cannot explain the abundances of EMP stars.3)Among the EMP stars, many C and N-rich stars with quite large rations of (C, N)/Fe have been discovered. we showed that such large rations can be explained with the black-hole-forming supernovae.4)Variations among the C-rich EMP stars can be explained with the mixing and the fallback mechanism.5)This implies many black-holes were formed from the first generation supernovae.6)Bipolar explosions induce naturally the mixing-fallback like events.