A CCD survey for contact binaries in six open clusters

The authors have surveyed six old and intermediate-age open clusters for contact binaries. Not a single W UMa binary was detected, while ≡3 were expected among the ≡1600 cluster stars examined. The authors conlude that contact binaries are at least as rare in the observed open clusters as they are in the field, and that they may be significantly more rare. NGC 188 remains unique in having seven W UMa stars among its ≡300 brightest members. The authors nondetection of even a single W UMa star among 545 members in the somewhat older cluster Mel 66 argues against great age being the parameter that determines whether a cluster is rich in contact binaries.