On Measuring the Metallicity of a Type Ia Supernova's Progenitor

TL;DR

This study investigates how progenitor metallicity influences spectral features in Type Ia Supernovae, proposing spectral signatures as indicators of progenitor composition to improve cosmological measurements.

Contribution

It introduces a method to link spectral features to progenitor metallicity using simulations, aiding in understanding supernova diversity and reducing Hubble constant uncertainties.

Findings

Spectral features at 4200 Å and 5200 Å deepen with higher metallicity.

Pseudo equivalent widths of these features correlate systematically with metallicity.

Proposed spectral indicators can differentiate progenitor metallicities in observed supernovae.

Abstract

In Type Ia Supernovae (\sneia), the relative abundances of chemical elements are affected by the neutron excess in the composition of the progenitor white dwarf. Since these products leave signatures in the spectra near maximum light, spectral features may be used to constrain the composition of the progenitor. We calculate the nucleosynthetic yields for three \snia simulations, assuming single degenerate, Chandrasekhar mass progenitors, for a wide range of progenitor metallicities, and calculate synthetic light curves and spectra to explore correlations between progenitor metallicity and the strength of spectral features. We use two 2D simulations of the deflagration-detonation-transition scenario with different $^{56}$Ni yields and the W7 simulation to control for differences between explosion models and total yields. While the overall yields of intermediate mass elements (16 $<$ A $\leq$ 40) differ between the three cases, trends in the yields are similar. With increasing metallicity, $^{28}$Si yields remain nearly constant, $^{40}$Ca yields decline, and Ti and $^{54}$Fe yields increase. In the synthetic spectra, we identify two features at 30 days post explosion that appear to deepen with progenitor metallicity: a Ti feature around 4200\,\AA\ and a Fe feature around 5200\,\AA\@. In all three simulations, their pseudo equivalent widths show a systematic trend with progenitor metallicity. This suggests that these two features may allow differentiation among progenitor metallicities of observed \sneia and potentially help reduce the intrinsic Hubble scatter.