Nucleosynthesis in Chandrasekhar Mass Models for Type Ia Supernovae and Constraints on Progenitor Systems and Burning-Front Propagation

摘要

We calculate explosive nucleosynthesis in Chandrasekhar mass models for TypeIa Supernovae(SNe Ia) to obtain new constraints on the rate of matter accretiononto the progenitor white dwarf and on the ignition density of central carbondeflagration. The calculated abundance of the Fe-group neutron-rich nuclei ishighly sensitive to the electron captures taking place in the central layers.The yields obtained from a slow central deflagration, and from a fastdeflagration or delayed detonation in the outer layers, are combined and put tocomparison with solar isotopic abundances. We found that (1) to avoid too largeratios of $^{54}$Cr/$^{56}$Fe and $^{50}$Ti/$^{56}$Fe, the ignition densityshould be as low as \ltsim 2 \e9 \gmc, and that (2) to avoid the overproductionof $^{58}$Ni and $^{54}$Fe, either the flame speed should not exceed a few % ofthe sound speed in the central low $Y_e$ layers, or the progenitor star has tobe metal-poor compared with solar. Such low central densities can be realizedby a rapid accretion as fast as $\dot M$ \gtsim 1 $\times$ 10$^{-7}$M$_\odot$yr$^{-1}$. In order to reproduce the solar abundance of $^{48}$Ca, one alsoneeds progenitor systems that undergo ignition at higher densities. We alsofound that the total amount of $^{56}$Ni, the Si-Ca/Fe ratio, and the abundanceof elements like Mn and Cr (incomplete Si-burning ashes), depend on the densityof the deflagration-detonation transition in delayed detonations. Ournucleosynthesis results favor transition densities slightly below 2.2$\times10^7$ g cm$^{-3}$.