The dependence of the evolution of SN type Ia progenitors on the C burning rate uncertainty and parameters of convective boundary mixing

Evolution of a supernova type Ia progenitor requires formation of a CO white dwarf, which implies a dependence on the C burning rate (CBR). It can also be affected by the recently identified possibility of C flame quenching by convective boundary mixing. Here, we present first results of our study of the combined effect of these two potential sources of uncertainty on the SN Ia progenitor evolution. We consider the possibility that the CBR could be higher than its currently recommended value by as much as a factor of 1000 at the relevant temperature if unidentified resonances are important, or that it could be significantly lower because of the hindrance effect. For stellar models that assume the Schwarzschild boundary for convection, the maximum initial mass for the formation of CO WDs increases from Mi = 5.5 Msun for the CBR factor of 1000 to Mi > 7.0 Msun for the CBR factor of 0.01. For C-flame quenching models, hybrid C-O-Ne WDs form for a range of initial mass of Delta Mi ~ 1 Msun, and therefore a significant fraction of stars that have previously been considered unavailable for SN Ia progenitors may in fact form WDs that will ignite C in a thermonuclear runaway. For the recommended CBR, the initial mass range for hybrid C-O-Ne WDs is 6.6Msun < Mi < 8.8 Msun, the larger initial mass corresponding to the larger WD mass. The most extreme case is found for the CBR factor of 0.1 that is supported by the hindrance model. When combined with a small amount of convective boundary mixing, that still causes C flame quenching, this nuclear physics assumption leads to the formation of a hybrid C-O-Ne WD with a mass of 1.3 Msun. If such WDs really exist, they do not need to accrete much mass to reach the Chandraskhar limit.

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Date added: Tue, 8 Oct 13