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

Abstract

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 .

A simple and general method for solving detailed chemical evolution with delayed production of iron and other chemical elements

“…We adopt the so-called 3/8-rule forth-order Runge-Kutta method to solve equation (8). Finally, we assume the stellar yields of Type Ia SNe from Iwamoto et al (1999).…”

Nucleosynthesis in Supernovae, Hypernovae/Gamma-ray Bursts and Compact Binary Mergers

“…Although there has been further progress since then, the review by Hillebrandt et al [21] gives an enlightening overview over all these options. The Mn/Fe ratio as a function of metallicity seems to be a sensitive measure whether near Chandrasekhar mass singledegenerate models (deflagrations like W7 [52] or delayed detonations [24,63]) occur at all, because only they show low Y e -regions close to the center of the WD. Mn comes in form of its only stable isotope 55 Mn, and is the decay product of 55 Co, produced in incomplete and complete Si-burning under optimal conditions with Y e = Z/A = 0.491.…”

Electron-capture Rates for pf-shell Nuclei in Stellar Environments and Nucleosynthesis

“…The problem of over-production of 58 Ni, 54 Cr and 54 Fe compared to the solar abundance was discussed [10] with the use of the capture rates of FFN [11]. A possible solution of the problem with slower e-capture rates was discussed in Ref.…”

“…The problem could be solved by using further slower e-capture rates of GXPF1J. Here, we use the W7 model [10] as an explosion model of type-Ia supernova explosions starting from C-O white dwarf with the mass of 1.38 solar mass. This model proceeds by a fast deflagration .…”

“…The over-production of 54 Fe which remained in the W7 model can be improved when we use an explosion model such as DD2 [10] with slow deflagration and delayed detonation. In this case, the over-production factor is suppressed within twice for all neutron-excess Cr, Fe and Ni isotopes [14].…”