Photometric variability in the old open cluster M 67 - II. General survey

We use dierential CCD photometry to search for variability in BVI among 990 stars projected in and around the old open cluster M 67. In a previous paper we reported results for 22 cluster members that are optical counterparts to X-ray sources; this study focuses on the other stars in our observations. A variety of sampling rates were employed, allowing variability on time scales ranging from0.3 hours to20 days to be studied. Among the brightest sources studied, detection of variability as small as 10 mmag is achieved (with >3 condence); for the typical star observed, sensitivity to variability at levels 20 mmag is achieved. The study is unbiased for stars with 12:5 <B< 18:5, 12:5 <V <18:5, and 12 <I <18 within a radius of about 10 arcmin from the cluster centre. In addition, stars with 10 <BV I <12:5 were monitored in a few small regions in the cluster. We present photometry for all 990 sources studied, and report the variability characteristics of those stars found to be variable at a statistically signicant level. Among the variables, we highlight several sources that merit future study, including stars located on the cluster binary sequence, stars on the giant branch, blue stragglers, and a newly discovered W UMa system.

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