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All the current r-process scenarios relevant to core-collapse supernovae are facing severe difficulties. In particular, recent core-collapse simulations with neutrino transport show no sign of neutron-rich wind from a proto-neutron star. In this paper, we discuss nucleosynthesis of the r-process in an alternative astrophysical site, “black hole wind”, which is the neutrino-driven outflow from the accretion torus around a black hole. This condition is assumed to be realized in double neutron star (or a neutron star a black hole) mergers or hypernovae. [ABSTRACT FROM AUTHOR]

The r-process in a low temperature environment is explored, in which the neutron emission by photodisintegration does not play a role. A semi-analytic neutrino-driven wind model is utilized for this purpose. The temperature in a supersonically expanding outflow can quickly drop to a few 108 K, where the (n,γ)-(γ,n) equilibrium is never achieved during the heavy r-nuclei synthesis. In addition, the neutron capture competes with the β-decay owing to the low matter density. Despite such non-standard physical conditions, a solar-like r-process abundance curve can be reproduced. The cold r-process predicts, however, the low lead production compared to that expected in the traditional r-process conditions, which can be a possible explanation for the low lead abundances found in a couple of r-process-rich Galactic halo stars. [ABSTRACT FROM AUTHOR]

Recent hydrodynamic simulations of core-collapse supernovae with accurate neutrino transport suggest that the bulk of the neutrino-heated ejecta is proton rich, in which the production of some interesting proton-rich nuclei is expected. However, there are a number of waiting point nuclei with the β+-lives of a few minutes, which prevent the production of heavy proton-rich nuclei beyond iron in explosive events such as core-collapse supernovae. In this study, it is shown that the rapid proton-capture (rp) process takes place by bypassing these waiting points via neutron-capture reactions even in the proton-rich environment, if there is an intense neutrino flux as expected during the early phase of the neutrino-driven winds of core-collapse supernovae. The nucleosynthesis calculations imply that the neutrino-driven winds can be potentially the origin of light p-nuclei including 92,94Mo and 96,98Ru, which cannot be explained by other astrophysical sites. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

We discuss production of light elements (Li, Be) in energetic type Ic supernovae (SNe Ic) and how newly synthesized light elements are transferred to stars of the next generation. We have pointed out that spallation reactions involving N and He become important in an explosion of a rotating metal-poor star if the progenitor still keeps a fraction of the He layer at SN explosion. In this kind of explosions, 6Li is produced by a fusion reaction He+He. Simultaneously, most of Be is produced through the spallation reaction He+N. This scenario suggests that there must be intrinsic scattering in abundance of Li isotopic ratios among metal-poor stars because the mass range of stars concerned here is limited to >= 40 M⊙ and light element yields should be sensitive to the degree of rotation. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Recent hydrodynamic studies of core-collapse supernovae imply that the neutrino-heated ejecta from a nascent neutron star develops to supersonic outflows and forms the wind termination shock. We investigate the effects of the termination shock in neutrino-driven winds and its role on the r-process. We find a couple of effects that can be relevant for the r-process. First is the sudden slowdown of the temperature decrease by the wind termination plays a decisive role to determine the r-process abundance curves. This is due to the strong dependences of the nucleosynthetic path on the temperature during the r-process freezeout phase. Second is the entropy jump by termination-shock heating, up to several 100NAk. We, however, find negligible roles of the entropy jump on the r-process. This is a consequence that the sizable entropy increase takes place only at a large shock radius (>=10,000 km) where the r-process has already ceased. [ABSTRACT FROM AUTHOR]