Binary Fraction Indicators in Resolved Stellar Populations and Supernova Type Ratios

TL;DR

This study investigates how varying binary star fractions influence stellar populations and supernova ratios, proposing that supernova subtype ratios can help constrain binary fractions across different galaxy environments.

Contribution

It introduces binary population synthesis models with mass-dependent binary fractions to analyze their effects on stellar and supernova populations, offering new diagnostic tools.

Findings

Wolf-Rayet subtype ratios are useful binary diagnostics but need large samples.

Uncertainties in stellar classification impact Wolf-Rayet diagnostics.

Supernova ratios could effectively constrain binary fractions in galaxy surveys.

Abstract

The binary fraction of a stellar population can have pronounced effects on its properties, and in particular the number counts of different massive star types, and the relative subtype rates of the supernovae which end their lives. Here we use binary population synthesis models with a binary fraction that varies with initial mass to test the effects on resolved stellar populations and supernovae, and ask whether these can constrain the poorly-known binary fraction in different mass and metallicity regimes. We show that Wolf-Rayet star subtype ratios are valuable binary diagnostics, but require large samples to distinguish by models. Uncertainties in which stellar models would be spectroscopically classified as Wolf-Rayet stars are explored. The ratio of thermonuclear, stripped envelope and other core-collapse supernovae may prove a more accessible test and upcoming surveys will be sufficient to constrain both the high mass and low mass binary fraction in the z < 1 galaxy population.