Reevaluating Old Stellar Populations

TL;DR

This paper introduces new stellar population synthesis models that include binary star evolution, providing improved fits to observed properties of old stellar populations and suggesting they may be younger and more metal-rich than previously thought.

Contribution

The paper presents a novel set of models that incorporate binary stellar evolution, enhancing the accuracy of age and metallicity estimates for old stellar populations.

Findings

Models with binary stars better match observed colours and spectral indices.

Best-fit populations are often younger than previous models.

Estimated metallicities are slightly higher with new models.

Abstract

Determining the properties of old stellar populations (those with age >1 Gyr) has long involved the comparison of their integrated light, either in the form of photometry or spectroscopic indexes, with empirical or synthetic templates. Here we reevaluate the properties of old stellar populations using a new set of stellar population synthesis models, designed to incorporate the effects of binary stellar evolution pathways as a function of stellar mass and age. We find that single-aged stellar population models incorporating binary stars, as well as new stellar evolution and atmosphere models, can reproduce the colours and spectral indices observed in both globular clusters and quiescent galaxies. The best fitting model populations are often younger than those derived from older spectral synthesis models, and may also lie at slightly higher metallicities.