A photometric study of the old open clusters Berkeley 73, Berkeley 75 and Berkeley 25 G. Carraro, D. Geisler, A. Moitinho, G. Baume and R. A. Vázquez A&A, 442 3 (2005) 917-924 Published online: 14 October 2005 DOI: 10.1051/0004-6361:20053089