Variable stars in the field of open cluster NGC 6939

TL;DR

This study presents a CCD photometric survey of the open cluster NGC 6939, identifying 22 variable stars including four cluster members, and uses contact binary analysis to support the cluster's distance and age.

Contribution

It provides new variable star detections in NGC 6939 and confirms cluster parameters through binary star analysis.

Findings

22 variable stars detected, 4 previously known

4 eclipsing binaries are cluster members

Distance to the cluster is supported as 1.74 kpc

Abstract

The results of CCD photometric survey performed with the 90/180 cm Schmidt-Cassegrain Telescope of the Nicolaus Copernicus University Astronomical Observatory in Piwnice (Poland) and the 70/172 cm Schmidt Telescope of the National Astronomical Observatory (NAO) at Rozhen (Bulgaria) of the field of 1 Gyr old open cluster NGC 6939 are presented. Twenty two variable stars were detected, four of them previously known. Four eclipsing systems (3 detached and 1 contact binary) were found to be members of the cluster. Analysis of the brightness of the contact binary V20 strongly supports the distance to the cluster of 1.74 +/- 0.20 kpc. The small population of contact binaries in NGC 6939 confirms also the relatively young age of the cluster.