The major uncertainties involved in the Chandrasekhar mass models for Type Ia supernovae (SNe Ia) are related to the companion star of their accreting white dwarf progenitor (which determines the accretion rate and consequently the carbon ignition density) and the flame speed after the carbon ignition. We calculate explosive nucleosynthesis in relatively slow deflagrations with a variety of deflagration speeds and ignition densities to put new constraints on the above key quantities. The abundance of the Fegroup, in particular of neutron-rich species like 48 Ca, 50 Ti, 54 Cr, 54,58 Fe, and 58 Ni, is highly sensitive to the electron captures taking place in the central layers. The yields obtained from such a slow central deflagration, and from a fast deflagration or delayed detonation in the outer layers, are combined and put to comparison with solar isotopic abundances. To avoid excessively large ratios of 54 Cr/ 56 Fe and 50 Ti/ 56 Fe, the central density of the "average" white dwarf progenitor at ignition should be as low as < ∼ 2 × 10 9 g cm −3 . To avoid the overproduction of 58 Ni and 54 Fe, either the flame speed should not exceed a few % of the sound speed in the central low Y e layers, or the metallicity of the average progenitors has to be lower than solar. Such low central densities can be realized by a rapid accretion as fast aṡ M > ∼ 1 × 10 −7 M ⊙ yr −1 . In order to reproduce the solar abundance of 48 Ca, one also needs progenitor systems that undergo ignition at higher densities. Even the smallest laminar flame speeds after the low-density ignitions would not produce sufficient amount of this isotope. We also found that the total amount of 56 Ni, the Si-Ca/Fe ratio, and the abundance of some elements like Mn and Cr (originating from incomplete Si-burning), depend on the density of the deflagration-detonation transition in delayed detonations. Our nucleosynthesis results favor transition densities slightly below 2.2×10 7 g cm −3 .

We calculate the evolution of heavy-element abundances from C to Zn in the solar neighborhood, adopting our new nucleosynthesis yields. Our yields are calculated for wide ranges of metallicity (Z ¼ 0YZ ) and the explosion energy (normal supernovae and hypernovae), based on the light-curve and spectra fitting of individual supernovae. The elemental abundance ratios are in good agreement with observations. Among the -elements, O, Mg, Si, S, and Ca show a plateau at ½Fe/H P À1, while Ti is underabundant overall. The observed abundance of Zn (½Zn/Fe $ 0) can be explained only by the high-energy explosion models, as it requires a large contribution of hypernovae. The observed decrease in the odd-Z elements (Na, Al, and Cu) toward low ½Fe/H is reproduced by the metallicity effect on nucleosynthesis. The iron-peak elements (Cr, Mn, Co, and Ni) are consistent with the observed mean values at À2:5 P ½Fe/H P À1, and the observed trend at the lower metallicity can be explained by the energy effect. We also show the abundance ratios and the metallicity distribution functions of the Galactic bulge, halo, and thick disk. Our results suggest that the formation timescale of the thick disk is $1Y3 Gyr.

Dust grains play a crucial role on formation and evolution history of stars and galaxies in the early universe. We investigate the formation of dust grains in the ejecta of population III supernovae including pair-instability supernovae which are expected to occur in the early universe, applying a theory of non-steady state nucleation and grain growth. Dust formation calculations are performed for core collapse supernovae with the progenitor mass M pr ranging from 13 to 30 M ⊙ and for pair-instability supernovae with M pr = 170 and 200 M ⊙ . In the calculations, the time evolution of gas temperature in the ejecta, which strongly affects the number density and size of newly formed grains, is calculated by solving the radiative transfer equation taking account of the energy deposition of radio active elements. Two extreme cases are considered for the elemental composition in the ejecta; unmixed and uniformly mixed cases within the He-core, and formation of CO and SiO molecules is assumed to be complete.The results of calculations for core collapse supernovae and pair-instability supernovae are summarized as the followings; in the unmixed ejecta, a variety of grain species condense, reflecting the difference of the elemental composition at the formation site in the ejecta, otherwise only oxide grains condense in the uniformly mixed ejecta. The average size of newly formed grains spans the range