Detection of new variable stars in the SMC cluster NGC 121

TL;DR

This study identifies new variable stars in the Small Magellanic Cloud cluster NGC 121 using image subtraction and detection methods, confirming its status as a young globular cluster.

Contribution

It introduces the first detection of variable stars in NGC 121 using advanced image analysis techniques, expanding knowledge of its stellar population.

Findings

27 RR Lyrae candidates identified on the Horizontal Branch

20 Dwarf Cepheid candidates detected in the cluster core

Results support NGC 121's classification as a young globular cluster

Abstract

New candidate variable stars have been identified in the Small Magellanic Cloud cluster NGC121, by applying both the image subtraction technique (ISIS, Alard 2000) and the Welch & Stetson (1993) detection method to HST WFPC2 archive and ACS proprietary images of the cluster. The new candidate variable stars are located from the cluster's Main Sequence up to Red Giant Branch. Twenty-seven of them fall on the cluster Horizontal Branch and are very likely RR Lyrae stars. They include the few RR Lyrae stars already discussed by Walker & Mack (1988). We also detected 20 Dwarf Cepheid candidates in the central region of NGC121. Our results confirm the "true" globular cluster nature of NGC121, a cluster that is at the young end of the Galactic globulars' age range.