We describe the construction of a database of extremely metal-poor (EMP) stars in the Galaxy. Our database contains detailed elemental abundances, reported equivalent widths, atmospheric parameters, photometry, and binarity status, compiled from papers in the literature that report on studies of EMP halo stars with [Fe=H] Ä 2.5. The compilation procedures for this database were designed to assemble data effectively from electronic tables available from online journals. We have also developed a data retrieval system that enables data searches by various criteria and illustrations to explore relationships between stored variables. Currently, our sample includes 1212 unique stars (many of which are studied by more than one group) with more than 15000 individual reported elemental abundances, covering relevant papers published by 2007 December. We discuss the global characteristics of the present database, as revealed by the EMP stars observed to date. For stars with [Fe=H] Ä 2.5, the number of giants with reported abundances is larger than that of dwarfs by a factor of two. The fraction of carbon-rich stars (among the sample for which the carbon abundance is reported) amounts to 30% for [Fe=H] Ä 2.5. We find that known binaries exhibit different distributions of the orbital period, according to whether they are giants or dwarfs, and also as a function of the metallicity, although the total sample of such stars is still quite small.

Abstract. We present sets of equation of state (EOS) of nuclear matter including hyperons using an SU f (3) extended relativistic mean field (RMF) model with a wide coverage of density, temperature, and charge fraction for numerical simulations of core collapse supernovae. Coupling constants of Σ and Ξ hyperons with the σ meson are determined to fit the hyperon potential depths in nuclear matter, U Σ (ρ 0 ) ≃ +30MeV and U Ξ (ρ 0 ) ≃ −15MeV, which are suggested from recent analyses of hyperon production reactions. At low densities, the EOS of uniform matter is connected with the EOS by Shen et al., in which formation of finite nuclei is included in the Thomas-Fermi approximation. In the present EOS, the maximum mass of neutron stars decreases from 2.17M ⊙ (N eµ) to 1.63M ⊙ (N Y eµ) when hyperons are included. In a spherical, adiabatic collapse of a 15M ⊙ star by the hydrodynamics without neutrino transfer, hyperon effects are found to be small, since the temperature and density do not reach the region of hyperon mixture, where the hyperon fraction is above 1 % (T > 40MeV or ρ B > 0.4 fm −3 ).

We discuss the characteristics of known extremely metal‐poor (EMP) stars in the Galaxy using the Stellar Abundances for Galactic Archaeology (SAGA) data base. We find the transition of the initial mass function to be at [Fe/H]∼−2 from the viewpoint of the distribution of carbon abundance and the frequency of carbon‐enhanced stars. Analyses of carbon‐enhanced stars in our sample suggest that nucleosynthesis in asymptotic giant branch (AGB) stars can contribute to carbon enrichment in a different way depending on whether the metallicity is above or below [Fe/H]∼−2.5, which is consistent with the current models of stellar evolution at low metallicity. For observed EMP stars, we confirm that some, though not all, observed stars might have undergone at least two types of extra mixing to change their surface abundances. One is the depletion of lithium abundance during the early phase of the red giant branch; the other is a decrease of the C/N ratio by one order of magnitude during the red giant branch phase. Observed small scatters of abundances for α‐elements and iron‐group elements suggest that the chemical enrichment of our Galaxy takes place in a well‐mixed interstellar medium. The abundance trends of α‐elements are highly correlated with each other including α‐enhanced and depleted stars, while the abundances of iron‐group elements are subject to different slopes relative to the iron abundance. This implies that the supernova yields of α‐elements are almost independent of mass and metallicity, while those of iron‐group elements have a metallicity dependence or mass dependence on the variable initial mass function. The occurrence of the hot‐bottom burning for M≳ 5 M⊙ is consistent with an initial mass function of the Galaxy peaked at ∼10–12 M⊙, compatible with the statistics of carbon‐enhanced stars with and without s‐process element enhancement and nitrogen‐enhanced stars. For s‐process elements, we find not only a positive correlation between carbon and s‐process element abundances, but also an increasing slope of the abundance ratio between them with increasing mass number of s‐process elements. The dominant site of the s‐process is still an open question because none of the known mechanisms for the s‐process is able to account for this observed correlation. In spite of the evidence of AGB evolution in observed abundances of EMP stars, any evidence of binary mass transfer is elusive by pursuing the effect of dilution in the convective envelope. We find the dependence of sulphur and vanadium abundances on the effective temperatures, in addition to the previously reported trends for silicon, scandium, titanium, chromium and cobalt.

-We investigate the emergence of strange baryons in the dynamical collapse of a non-rotating massive star to a black hole by the neutrino-radiation hydrodynamical simulations in general relativity. By following the dynamical formation and collapse of nascent proto-neutron star from the gravitational collapse of a 40M ⊙ star adopting a new hyperonic EOS table, we show that the hyperons do not appear at the core bounce but populate quickly at ∼0.5-0.7 s after the bounce to trigger the re-collapse to a black hole. They start to show up off center owing to high temperatures and later prevail at center when the central density becomes high enough. The neutrino emission from the accreting protoneutron star with the hyperonic EOS stops much earlier than the corresponding case with a nucleonic EOS while the average energies and luminosities are quite similar between them. These features of neutrino signal are a potential probe of the emergence of new degrees of freedom inside the black hole forming collapse.