A point source survey of M31 with the Spitzer Space Telescope

TL;DR

This study uses Spitzer infrared observations to analyze the stellar populations of M31, highlighting the prominence of red supergiants and AGB stars, and comparing their distributions to those in M33.

Contribution

First infrared survey of M31's stellar population using Spitzer, identifying key evolved stars and comparing their populations to M33.

Findings

Red supergiants are the brightest infrared objects in M31.

Many luminous AGB stars are detected, including long period variables.

The AGB carbon star population in M31 appears sparse compared to M33.

Abstract

We explore the stellar population of M31 in a Spitzer Space Telescope survey utilizing IRAC and MIPS observations. Red supergiants are the brightest objects seen in the infrared; they are a prominent evolutionary phase. Due to their circumstellar envelopes, many of these radiate the bulk of their luminosity at IRAC wavelengths and do not stand out in the near infrared or optically. Going fainter, we see large numbers of luminous asymptotic giant branch (AGB) stars, many of which are known long period variables. Relative to M33, the AGB carbon star population of M31 appears sparse, but this needs to be spectroscopically confirmed.