BS196: an old star cluster far from the SMC main body

TL;DR

This study provides detailed photometric analysis of the old star cluster BS196 in the SMC, revealing its age, metallicity, structure, and faintness, contributing to understanding of SMC's oldest clusters.

Contribution

First detailed photometric and structural analysis of BS196, one of the oldest and faintest star clusters in the SMC, expanding knowledge of its stellar populations and properties.

Findings

BS196 is approximately 5 Gyr old.

Metallicity is estimated at [Fe/H]=-1.68.

BS196 is a faint, loose cluster with specific structural parameters.

Abstract

We present B and V photometry of the outlying SMC star cluster BS196 with the 4.1-m SOAR telescope. The photometry is deep (to V~25) showing ~3 mag below the cluster turnoff point (TO) at Mv=2.5 (1.03 Msun). The cluster is located at the SMC distance. The CMD and isochrone fittings provide a cluster age of 5.0+-0.5 Gyr, indicating that this is one of the 12 oldest clusters so far detected in the SMC. The estimated metallicity is [Fe/H]=-1.68+-0.10. The structural analysis gives by means of King profile fittings a core radius Rc=8.7+-1.1 arcsec (2.66+-0.14 pc) and a tidal radius Rt=69.4+-1.7 arcsec (21.2+-1.2 pc). BS196 is rather loose with a concentration parameter c=0.90. With Mv=-1.89+-0.39, BS196 belongs to the class of intrinsically fainter SMC clusters, as compared to the well-known populous ones, which starts to be explored.