The Evolution and Explosion of Massive Stars. II. Explosive Hydrodynamics and Nucleosynthesis

The nucleosynthetic yield of isotopes lighter than A = 66 (zinc) is determined for a grid of stellar masses and metallicities including stars of 11, 12, 13, 15, 18, 19, 20, 22, 25, 30, 35, and 40 M_sun and metallicities Z = 0, l0^-4, 0.01, 0.1, and 1 times solar (a slightly reduced mass grid is employed for nonsolar metallicities). Altogether 78 different model supernova explosions are calculated. In each case nucleosynthesis has already been determined for 200 isotopes in each of 600 to 1200 zones of the presupernova star, including the effects of time dependent convection. Here each star is exploded using a piston to give a specified final kinetic energy at infinity (typically 1.2 × 10⁵¹ ergs), and the explosive modifications to the nucleosynthesis, including the effects of neutrino irradiation, determined. A single value of the critical ¹²C(α,γ) ¹⁶O reaction rate corresponding to 8(300 keV) = 170 keV barns is used in all calculations. The synthesis of each isotope is discussed along with its sensitivity to model parameters. In each case, the final mass of the collapsed remnant is also determined and often found not to correspond to the location of the piston (typically the edge of the iron core), but to a "mass cut" farther out. This mass cut is sensitive not only to the explosion energy, but also to the presupernova structure, stellar mass, and the metallicity. Unless the explosion mechanism, for unknown reasons, provides a much larger characteristic energy in more massive stars, it appears likely that stars larger than about 30 M_sun will experience considerable reimplosion of heavy elements following the initial launch of a successful shock. While such explosions will produce a viable, bright Type II supernova light curve, lacking perhaps the radioactive tail, they will have dramatically reduced yields of heavy elements and may leave black hole remnants of up to 10 and more solar masses. The production of black holes may be particularly favored for stars of low metallicity, both because of their more compact structure and reduced mass loss.