NUCLEOSYNTHESIS AND EVOLUTION OF MASSIVE METAL-FREE STARS

Abstract

The evolution and explosion of metal-free stars with masses 10--100 solar masses are followed, and their nucleosynthetic yields, light curves, and remnant masses determined. When the supernova yields are integrated over a Salpeter initial mass function, the resulting elemental abundance pattern is qualitatively solar, but with marked deficiencies of odd-Z elements with 7 <= Z <= 13. Neglecting the contribution of the neutrino wind from the neutron stars that they make, no appreciable abundances are made for elements heavier than germanium. The computed pattern compares favorably with what has been observed in metal-deficient stars with [Z] ~< -3. Most of the stars end their lives as blue supergiants and make supernovae with distinctive light curves resembling SN 1987A, but some produce primary nitrogen by dredge up and become red supergiants. A novel automated fitting algorithm is developed for determining optimal combinations of explosion energy, mixing, and initial mass function in the large model data base to agree with specified data sets. The model is applied to the low metallicity sample of Cayrel et al. (2004) and the two ultra-iron-poor stars HE0107-5240 and HE1327-2326. Best agreement with these low metallicity stars is achieved with very little mixing, and none of the metal-deficient data sets considered show the need for a high energy explosion component. To the contrary, explosion energies somewhat less than 1.2 B seem to be preferred in most cases. (abbreviated)