Infrared variable stars in the compact elliptical galaxy M32

TL;DR

This study identifies and characterizes variable stars in galaxy M32 using multi-epoch infrared observations from Spitzer, revealing a population of asymptotic giant branch stars and finding no evidence of a younger stellar population.

Contribution

First infrared variability catalog of M32, identifying candidate long-period variables and analyzing their properties with high confidence.

Findings

83 candidate variable stars identified

28 high-confidence variables confirmed

No evidence of a younger stellar population in M32

Abstract

Variable stars in the compact elliptical galaxy M32 are identified, using three epochs of photometry from the Spitzer Space Telescope at 3.6 and 4.5 $\mu$m, separated by 32 to 381 days. We present a high-fidelity catalogue of sources detected in multiple epochs at both 3.6 and 4.5 $\mu$m, which we analysed for stellar variability using a joint probability error-weighted flux difference. Of these, 83 stars are identified as candidate large-amplitude, long-period variables, with 28 considered high-confidence variables. The majority of the variable stars are classified as asymptotic giant branch star candidates using colour-magnitude diagrams. We find no evidence supporting a younger, infrared-bright stellar population in our M32 field.