The Nucleosynthetic Signature of Population III

Growing evidence suggests that the first generation of stars may have beenquite massive (~100-300 M_sun). Could these stars have left a distinctnucleosynthetic signature? We explore the nucleosynthesis of helium cores inthe mass range M_He=64 to 133 Msun, corresponding to main-sequence star massesof approximately 140 to 260 M_sun. Above M_He=133 M_sun, without rotation andusing current reaction rates, a black hole is formed and no nucleosynthesis isejected. For lighter helium core masses, ~40 to 63 M_sun, violent pulsationsoccur, induced by the pair instability and accompanied by supernova-like massejection, but the star eventually produces a large iron core in hydrostaticequilibrium. It is likely that this core, too, collapses to a black hole, thuscleanly separating the heavy element nucleosynthesis of pair instabilitysupernovae from those of other masses, both above and below. Indeed, black holeformation is a likely outcome for all Population III stars with main sequencemasses between about 25 M_sun and 140 M_sun (M_He = 9 to 63 M_sun) as well asthose above 260 M_sun. Nucleosynthesis in pair-instability supernovae variesgreatly with the mass of the helium core which determines the maximumtemperature reached during the bounce. At the upper range of exploding coremasses, a maximum of 57 M_sun of Ni56 is produced making these the mostenergetic and the brightest thermonuclear explosions in the universe.Integrating over a distribution of masses, we find that pair instabilitysupernovae produce a roughly solar distribution of nuclei having even nuclearcharge, but are remarkably deficient in producing elements with odd nuclearcharge. Also, essentially no elements heavier than zinc are produced due to alack of s- and r-processes.Comment: 20 pages, including 5 figures; accepted by Ap