Nucleosynthesis and Evolution of Massive Metal-Free Stars

TL;DR

This paper models the evolution and nucleosynthesis of metal-free stars, comparing predictions with observed metal-poor stars, and introduces an automated fitting algorithm for supernova explosion parameters.

Contribution

It provides detailed models of zero-metallicity star evolution and nucleosynthesis, and develops a novel automated method to fit supernova parameters to observed data.

Findings

Elemental abundance patterns are roughly solar with odd-Z deficiencies.

Most stars end as blue supergiants with SN 1987A-like light curves.

Low explosion energies (<1.2 B) fit observed metal-poor stars best.

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)