Photometric study of the star cluster NGC 2155 in the Large Magellanic Cloud: age estimation and variable stars

TL;DR

This study provides new photometric data for NGC 2155, estimating its age at approximately 2.25 billion years, identifying seven variable stars, and highlighting potential for distance measurement through a binary system.

Contribution

It offers the first deep photometry and variable star analysis of NGC 2155, determining its age, metallicity, and variable star content with new observational data.

Findings

Estimated cluster age ~2.25 Gyr

Detected 7 variable stars including SX Phe and eclipsing binary

Identified a candidate for distance measurement

Abstract

We present results of new photometry for the globular star cluster NGC 2155 in the Large Magellanic Cloud (LMC). Our I- and V-band observations were obtained with the 6.5-meter Magellan 1 Baade Telescope at Las Campanas Observatory resulting in deep photometry down to V ~ 24 mag. By analyzing the color-magnitude diagram for the cluster and utilizing the Victoria-Regina grid of isochrones models we estimated the age of the cluster at ~ 2.25 Gyr and [Fe/H]=-0.71, the numbers which place NGC 2155 outside the age-gap in the age-metallicity relation for LMC clusters. Using the Difference Image Analysis Package (DIAPL), we detected 7 variable stars in the cluster field with variability at the level of 0.01 magnitude in the I-band. Three variables are particularly interesting: two SX Phoenicis (SX Phe) stars pulsating in the fundamental mode, and a detached eclipsing binary which is a prime candidate to estimate the distance to the cluster.