Type Ia Supernova Explosions from Hybrid Carbon-Oxygen-Neon White Dwarf Progenitors That Have Mixed During Cooling

TL;DR

This study investigates hybrid white dwarf progenitors with mixed compositions and their potential to produce type Ia supernovae, revealing that mixing affects explosion yields and nucleosynthesis outcomes.

Contribution

It introduces a new simulation approach for hybrid white dwarf progenitors considering mixing effects during cooling, comparing their explosion yields to traditional models.

Findings

Hybrid progenitors produce less 56Ni than traditional C-O white dwarfs.

Mixing during cooling influences the distribution of elements in supernova explosions.

Higher central density in hybrid models affects ignition and nucleosynthesis.

Abstract

The creation of "hybrid" white dwarfs, made of a C-O core within a O-Ne shell has been proposed, and studies indicate that ignition in the C-rich central region makes these viable progenitors for thermonuclear (type Ia) supernovae. Recent work found that the C-O core is mixed with the surrounding O-Ne as the white dwarf cools prior to accretion, which results in lower central C fractions in the massive progenitor than previously assumed. To further investigate the efficacy of hybrid white dwarfs as progenitors of thermonuclear supernovae, we performed simulations of thermonuclear supernovae from a new series of hybrid progenitors that include the effects of mixing during cooling. The progenitor white dwarf model was constructed with the one-dimensional stellar evolution code MESA and represented a star evolved through the phase of unstable interior mixing followed by accretion until it reached conditions for the ignition of carbon burning. This MESA model was then mapped to a two-dimensional initial condition for explosions simulated with FLASH. For comparison, similar simulations were performed for a traditional C-O progenitor white dwarf. By comparing the yields of the explosions, we find that, as with earlier studies, the lower C abundance in the hybrid progenitor compared to the traditional C-O progenitor leads to a lower average yield of 56Ni. Although the unmixed hybrid WD showed a similar decrement also in total iron group yield, the mixed case does not and produces a smaller fraction of iron group elements in the form of 56Ni. We attribute this to the higher central density required for ignition and the location, center or off-center, of deflagration ignition.