Photometric variability in the old open cluster M 67^*,**

II. General survey

¹ Department of Astronomy, University of Wisconsin, 475 N Charter St, Madison WI 53706, USA
² Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate (LC), Italy
³ Astronomical Institute, PO Box 80000, 3508 TA Utrecht, The Netherlands

Corresponding author: K. Stassun, keivan@astro.wisc.edu

Received: 26 September 2001
Accepted: 5 December 2001

Abstract

We use differential 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 from ~0.3 hours to ~20 days to be studied. Among the brightest sources studied, detection of variability as small as  mmag is achieved (with > confidence); for the typical star observed, sensitivity to variability at levels  mmag is achieved. The study is unbiased for stars with , , and within a radius of about 10 arcmin from the cluster centre. In addition, stars with 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 significant 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.