Nucleosynthesis in hypernovae and extremely metal-poor stars Original Research Article

Hypernovae are the core-collapse supernovae with very large explosion energies (⪆ 1052 ergs). Nucleosynthesis in hypernovae show the following characteristics: 1) Higher energy explosions tend to produce larger [(Zn, Co, V)/Fe] and smaller [(Mn, Cr)/Fe], which can explain the trend observed in very metal-poor stars. 2) Because of enhanced α-rich freezeout, 44Ca, 48Ti, and 64Zn are produced more abundantly than in normal supernovae. The large [(Ti, Zn)/Fe]ratios observed in very metal-poor stars strongly suggest a significant contribution of hypernovae. 3) Oxygen burning takes place in more extended regions in hypernovae, which makes the Si/O ratio larger. We thus suggest that hypernovae make important contribution to the early Galactic (and cosmic) chemical evolution. We then discuss the evolutionary origin of the recently discovered most Fe deficient star, HE0107-5240. We show that the abundance pattern of HE0107-5240 and other extremely metal-poor (EMP) stars are in good accord with those of supernovae which originate from ∼ 20–130 M⊙ stars and form ∼ 3–10 M⊙ black holes.