Astrometric monitoring of the binary brown dwarf DENIS-P J1228.2-1547 W. Brandner, E. L. Martín, H. Bouy, R. Köhler, X. Delfosse, G. Basri and M. Andersen A&A, 428 1 (2004) 205-208 Published online: 23 November 2004 DOI: 10.1051/0004-6361:20041912