Red Supergiants in the Local Group

TL;DR

This paper reviews recent research on red supergiants in the Local Group, highlighting metallicity effects on their evolution, mass loss, and spectral variability, and discusses implications for stellar evolution models.

Contribution

It provides a comprehensive synthesis of recent observational and theoretical studies on RSGs across diverse Local Group environments, emphasizing metallicity-dependent trends.

Findings

Metallicity influences RSG effective temperatures and masses.

Unusual spectral variability observed in some extragalactic RSGs.

Host environment correlates with dust production in RSGs.

Abstract

Galaxies in the Local Group span a factor of 15 in metallicity, ranging from the super-solar M31 to the Wolf-Lundmark-Melotte (WLM) galaxy, which is the lowest-metallicity (0.1xZsun) Local Group galaxy currently forming stars. Studies of massive star populations across this broad range of environments have revealed important metallicity-dependent evolutionary trends, allowing us to test the accuracy of stellar evolutionary tracks at these metallicities for the first time. The RSG population is particularly valuable as a key mass-losing phase of moderately massive stars and a source of core-collapse supernova progenitors. By reviewing recent work on the RSG populations in the Local Group, we are able to quantify limits on these stars' effective temperatures and masses and probe the relationship between RSG mass loss behaviors and host environments. Extragalactic surveys of RSGs have also revealed several unusual RSGs that display signs of unusual spectral variability and dust production, traits that may potentially also correlate with the stars' host environments. I will present some of the latest work that has progressed our understanding of RSGs in the Local Group, and consider the many new questions posed by our ever-evolving picture of these stars.