Photometric variability in the open cluster M 67 - I. Cluster members detected in X-rays M. van den Berg, K. G. Stassun, F. Verbunt and R. D. Mathieu A&A, 382 3 (2002) 888-898 Published online: 15 February 2002 DOI: 10.1051/0004-6361:20011521