Variable stars in the field of the open cluster NGC 6939

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 the 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 I 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 circle dot 0.20 kpc. The small population of contact binaries in NGC 6939 confirms also the relatively young age of the cluster. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.