Exploring the Carbon Simmering Phase: Reaction Rates, Mixing, and the Convective Urca Process
18 Dec 2017The Astrophysical Journal, Volume 851, Issue 2, article id. 105, 7 pp.
Josiah Schwab, Héctor Martínez-Rodríguez, Anthony L. Piro, and Carles Badenes
The neutron excess at the time of explosion provides a powerful discriminant among models of Type Ia supernovae. Recent calculations of the carbon simmering phase in single degenerate progenitors have disagreed about the final neutron excess. We find that the treatment of mixing in convection zones likely contributes to the difference. We demonstrate that in Modules for Experiments in Stellar Astrophysics models, heating from exothermic weak reactions plays a significant role in raising the temperature of the white dwarf. This emphasizes the important role that the convective Urca process plays during simmering. We briefly summarize the shortcomings of current models during this phase. Ultimately, we do not pinpoint the difference between the results reported in the literature, but show that the results are consistent with different net energetics of the convective Urca process. This problem serves as an important motivation for the development of models of the convective Urca process suitable for incorporation into stellar evolution codes.