Supernova Type Ia progenitors from merging double white dwarfs: Using a new population synthesis model

TL;DR

This paper develops a new population synthesis model to evaluate the contribution of merging double white dwarfs to Type Ia supernovae, comparing two common envelope evolution formalisms and analyzing their impact on observed supernova rates.

Contribution

The study introduces an updated population synthesis model incorporating two CE formalisms, providing insights into their effects on SNIa progenitor populations and rates.

Findings

Gamma-formalism better matches observed double white dwarf populations.

Simulated SNIa rates are 7-12 times lower than observed.

Delay time distribution morphology aligns with observations within errors.

Abstract

The study of Type Ia supernovae (SNIa) has lead to greatly improved insights into many fields in astrophysics, however a theoretical explanation of the origin of these events is still lacking. We investigate the potential contribution to the SNIa rate from the population of merging double carbon-oxygen white dwarfs. We aim to develope a model that fits the observed SNIa progenitors as well as the observed close double white dwarf population. We differentiate between two scenarios for the common envelope (CE) evolution; the alpha-formalism based on the energy equation and the gamma-formalism that is based on the angular momentum equation. In one model we apply the alpha-formalism always. In the second model the gamma-formalism is applied, unless the binary contains a compact object or the CE is triggered by a tidal instability for which the alpha-formalism is used. The binary population synthesis code SeBa was used to evolve binary systems from the zero-age main sequence to the formation of double white dwarfs and subsequent mergers. SeBa has been thoroughly updated since the last publication of the content of the code. The limited sample of observed double white dwarfs is better represented by the simulated population using the gamma-formalism than the alpha-formalism. For both CE formalisms, we find that although the morphology of the simulated delay time distribution matches that of the observations within the errors, the normalisation and time-integrated rate per stellar mass are a factor 7-12 lower than observed. Furthermore, the characteristics of the simulated populations of merging double carbon-oxygen white dwarfs are discussed and put in the context of alternative SNIa models for merging double white dwarfs.