Evidence for coronal activity cycles on 61 Cygni A and B A. Hempelmann, J. H. M. M. Schmitt, S. L. Baliunas and R. A. Donahue A&A, 406 2 (2003) L39-L42 Published online: 17 November 2003 DOI: 10.1051/0004-6361:20030882