Variable stars in the field of the old open cluster Melotte 66

TL;DR

This study identifies ten variable stars in Melotte 66, including eclipsing binaries and a potential blue straggler, and analyzes the cluster's stellar population and effects causing its wide main sequence.

Contribution

First detailed photometric survey of Melotte 66 revealing new variables and clarifying the causes of its wide main sequence.

Findings

Nine new variable stars discovered, including eight eclipsing binaries.

Four contact binaries are likely cluster members based on distance estimates.

The wide main sequence is due to variable reddening and binary star population.

Abstract

We report the results of photometric monitoring of the Melotte 66 field in BVI filters. Ten variables were identified with nine being new discoveries. The sample includes eight eclipsing binaries of which four are W UMa type stars, one star is a candidate blue straggler. All four contact binaries are likely members of the cluster based on their estimated distances. Ten blue stars with U-B<-0.3 were detected inside a 14.8 x 22.8 arcmin^2 field centred on the cluster. Time series photometry for 7 of them showed no evidence for any variability. The brightest object in the sample of blue stars is a promising candidate for a hot subdwarf belonging to the cluster. We show that the anomalously wide main sequence of the cluster, reported in some earlier studies, results from a combination of two effects: variable reddening occuring across the cluster field and the presence of a rich population of binary stars in the cluster itself. The density profile of the cluster field is derived and the total number of member stars with 16<V<21 or 2.8<M_{V}<7.8 is estimated conservatively at about 1100.