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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]

Observed large scatters in abundance ratios of neutron-capture elements relative to iron in metal-poor stars may suggest incomplete mixing of the interstellar medium at the beginning of the Galaxy. On the other hand, recent studies of metal-poor stars show considerable small dispersions for abundance ratios of C-Zn. We discuss whether such variations of scatters in abundance ratios can be explained by a consistent chemical evolution model. We also attempt to constrain the origins of r-process elements, comparing predictions by an inhomogeneous chemical evolution model with new observational results with Subaru HDS. © 2006 American Institute of Physics [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]

We present detailed abundance measurements of neutron-capture elements for very metal-poor stars. We obtained very high quality, near-UV spectra of four bright metal-poor stars using Subaru/HDS, and determined the abundances of many neutron-capture elements. We investigated the detailed abundance patterns of moderately neutron-capture-enhanced-stars and neutron-capture-poor-stars, and clarified the difference in the abundance patterns. We focus on the well-known metal-poor giant HD122563, in which 19 neutron-capture elements including Nb, Mo, Ru, Pd, Ag, Pr, and Sm have been detected by the present work. Our new results clearly demonstrate that the elemental abundances more steeply decrease with increasing atomic number than those of the r-process component in solar-system material. Especially, the tendency that the abundance continuously decreases in the region of 38 ≤ Z ≤ 47 does not agree with any neutron-capture processes known (i.e., main s-process, weak s-process, or main r-process). Since the abundance pattern of such very metal-poor stars, in contrast to that of solar system material, is expected to be formed by a small number of nucleosynthesis events, another process yielding elements with 38 ≤ Z ≤ 47 would be required. This result will give a new, strong constraint on the modeling of the process that has provided light neutron-capture elements in the very early Galaxy. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

We investigate energetic type Ic supernovae as a production site for 6Li and other light elements in the early stage of the Milky Way. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]