Type Ia supernovae from chemically segregated white dwarfs

TL;DR

This study investigates how chemical segregation of impurities like $^{22}$Ne and $^{56}$Fe in white dwarf interiors affects the nucleosynthesis yields and observable properties of Type Ia supernovae, revealing significant impacts on diagnostic isotope ratios.

Contribution

It introduces a detailed analysis of chemical segregation effects on supernova yields using a one-dimensional model, highlighting changes in isotope production and progenitor indicators.

Findings

Yields of key isotopes like manganese are significantly affected.

Chemical segregation influences progenitor metallicity indicators.

Main explosion properties like kinetic energy vary only slightly.

Abstract

Type Ia supernovae are the outcome of the explosion of a carbon-oxygen white dwarf in a close binary system. They are thought to be the main contributors to the galactic nucleosynthesis of iron-peak elements, with important contributions to the yields of intermediate mass elements. Recent analyses of the phase diagram of carbon and oxygen containing impurities such as $^{22}$Ne and $^{56}$Fe in conditions relevant to white dwarf interiors suggest that both isotopes can partially separate when the temperature of the star is low enough to start solidifying. The purpose of this paper is to examine the impact of such a segregation on the yields of the different chemical species synthesized during explosions. A one-dimensional supernova code has been used to evaluate the impact of the sedimentation assuming different degrees of chemical separation. It is found that the main properties of the ejecta, kinetic energy and ejected mass of $^{56}$Ni do only vary slightly when the separation is taken into account. However, the yields of important isotopes that are used as diagnostic tools such as manganese can be strongly modified. Furthermore, the chemical segregation studied here is able to change several indicators related to progenitor metallicity (such as the mass ratio of calcium to sulphur in the ejecta or the UV flux of the supernova) and to its mass, whether it is a Chandrasekhar-mass white dwarf or a substantially lighter one (such as the imprint of stable nickel on late-time infrared spectra or those related to the presence of radioactive nickel at the centre of the ejecta).