Exploring the diversity of double detonation explosions for type Ia supernovae: Effects of the post-explosion helium shell composition

TL;DR

This study investigates how the composition of helium shells in double detonation models affects the light curves and spectra of type Ia supernovae, showing potential explanations for observed light curve bumps and conditions for normal supernovae.

Contribution

It systematically explores the effects of post-explosion helium shell compositions on supernova light curves, highlighting conditions under which double detonation models align with observations.

Findings

Models with iron-group elements in the shell produce light curve bumps matching some observed supernovae.

Shells without iron-group elements fit well with normal SNe Ia from early times to maximum light.

Certain compositions can reproduce the diversity of observed supernova light curves and colors.

Abstract

The detonation of a helium shell on top of a carbon-oxygen white dwarf has been argued as a potential explosion mechanism for type Ia supernovae (SNe~Ia). The ash produced during helium shell burning can lead to light curves and spectra that are inconsistent with normal SNe~Ia, but may be viable for some objects showing a light curve bump within the days following explosion. We present a series of radiative transfer models designed to mimic predictions from double detonation explosion models. We consider a range of core and shell masses, and systematically explore multiple post-explosion compositions for the helium shell. We find that a variety of luminosities and timescales for early light curve bumps result from those models with shells containing $^{56}$Ni, $^{52}$Fe, or $^{48}$Cr. Comparing our models to SNe~Ia with light curve bumps, we find that these models can reproduce the shapes of almost all of the bumps observed, but only those objects with red colours around maximum light ($B-V \gtrsim 1$) are well matched throughout their evolution. Consistent with previous works, we also show that those models in which the shell does not contain iron-group elements provide good agreement with normal SNe~Ia of different luminosities from shortly after explosion up to maximum light. While our models do not amount to positive evidence in favour of the double detonation scenario, we show that provided the helium shell ash does not contain iron-group elements, it may be viable for a wide range of normal SNe~Ia.