Type Ia supernovae from chemically segregated white dwarfs

¹ Departamento de Física Teórica y del Cosmos, Universidad de Granada, 18071 Granada, Spain
e-mail: eduardo.bravo@ugr.es
² Institut de Ciències de l’Espai (ICE, CSIC), Campus UAB, C/ de Can Magrans s/n, 08193 Cerdanyola del Vallès, Spain
³ Institut d’Estudis Espacials de Catalunya (IEEC), C/ Gran Capità 2-4, 08034 Barcelona, Spain
⁴ Observatori Fabra, Mathematics and Astronomy Section (RACAB), Rambla dels Estudis 115, planta 1a, 08002 Barcelona, Spain
⁵ INAF – Osservatorio Astronomico d’Abruzzo, via Mentore Maggini, snc, 64100 Teramo, Italy
⁶ INFN – Sezione di Perugia, via Pascoli, Perugia, Italy

Received: 6 October 2023
Accepted: 16 January 2024

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 ²²Ne and ⁵⁶Fe 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 the present paper is to examine the impact of this separation on the yields of the different chemical species synthesized during explosions. We used a one-dimensional supernova code to evaluate the impact of the sedimentation assuming different degrees of chemical separation. We find that the main properties of the ejecta, the kinetic energy, and the ejected mass of ⁵⁶Ni 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 separation studied here is able to change several indicators related to the metallicity of the progenitor (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 that related to the presence of radioactive nickel at the center of the ejecta).