The Nucleosynthetic Signature of Population III

Growing evidence suggests that the first generation of stars may have been quite massive ( ∼ 100 − 300 M⊙). Could these stars have left a distinct nucleosynthetic signature? We explore the nucleosynthesis of helium cores in the mass range MHe = 64 to 133M⊙, corresponding to main-sequence star masses of approximately 140 to 260M⊙. Above MHe = 133 M⊙, without rotation and using current reaction rates, a black hole is formed and no nucleosynthesis is ejected. For lighter helium core masses, ∼40 to 63M⊙, violent pulsations occur, induced by the pair instability and accompanied by supernova-like mass ejection, but the star eventually produces a large iron core in hydrostatic equilibrium. It is likely that this core, too, collapses to a black hole, thus cleanly separating the heavy element nucleosynthesis of pair instability supernovae from those of other masses, both above and below. Indeed, black hole formation is a likely outcome for all Population III stars with main sequence masses between about 25 M ⊙ and 140M ⊙ (MHe = 9 to 63M⊙) as well as those above 260M⊙. Nucleosynthesis in pair-instability supernovae varies greatly with the mass of the helium core which determines the maximum temperature reached during the bounce. At the upper range of exploding core masses, a maximum of 57M⊙