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Session 17 - Supernovae.
Display session, Monday, January 15
North Banquet Hall, Convention Center
Among the major uncertainties involved in the Chandrasekhar mass models for Type Ia supernovae (SNe Ia) are the companion star of the accreting white dwarf (or the accretion rate that determines the carbon ignition density) and the flame speed after ignition. To constrain the accretion rate from nucleosynthesis point of view, we calculate explosive nucleosynthesis in a carbon deflagration wave that propagates at a speed v_def as slow as 1.5 - 3 % of the sound speed v_s as suggested from recent multi-dimensional simulations. In the deflagration wave, electron capture enhances neutron excess, which depends on both v_def and the central density of the white dwarf \rho_9 = \rho_c/10^9 g cm^-3. We adopt two cases of \rho_9 = 1.3 and 2.4 at the thermonuclear runaway. Because of slow propagation, a significant amount of neutron-rich species such as ^54Cr, ^50Ti, ^58Fe, ^62Ni, etc. are synthesized in the central region. For v_def = 0.015 v_s and \rho_9 = 2.4, for example, the ratios of ^54Cr/^56Fe and ^50Ti/^56Fe exceed the solar ratios by a factor of \sim 20 and 15, respectively, assuming 0.6 M_ødot ^56Ni production in the outer layers of SNe Ia. For \rho_9 = 1.3, the excess of the ^54Cr/^56Fe ratio over the solar is a factor of \sim 4, which seems to be marginally consistent with the solar abundances if about a half of the solar ^56Fe originate from SNe Ia. Therefore, the Chandrasekhar mass models should have \rho_9 < 1.3, which can be realized by such a rapid accretion as \dot M > 5 \times 10^-7 M_ødot yr^-1. Such rapidly accreting white dwarfs might correspond to the super-soft X-ray sources.
