M32: Is There An Ancient, Metal-Poor Population?

TL;DR

This study uses Hubble Space Telescope observations to detect RR Lyrae stars in M32, providing evidence for an ancient, metal-poor stellar population in the galaxy through variability analysis.

Contribution

The paper presents the first detection of RR Lyrae stars in M32, indicating the presence of a very old stellar population using deep time-series imaging.

Findings

Detected 31 RR Lyrae stars in M32 fields

Confirmed existence of an ancient, metal-poor population in M32

Provided detailed variability data for old stellar populations

Abstract

We observed two fields near M32 with the ACS/HRC on board the Hubble Space Telescope, located at distances of about 1.8' and 5.4' (hereafter F1 and F2, respectively) from the center of M32. To obtain a very detailed and deep color-magnitude diagram (CMD) and to look for short period variability, we obtained time-series imaging of each field in 32-orbit-long exposures using the F435W (B) and F555W (V) filters, spanning a temporal range of 2 days per filter. We focus on our detection of variability on RR Lyrae variable stars, which represents the only way to obtain information about the presence of a very old population (larger than 10 Gyr) in M32 from optical data. Here we present results obtained from the detection of 31 RR Lyrae in these fields: 17 in F1 and 14 in F2.