Photometric variability of young brown dwarfs in the Orionis open cluster J. A. Caballero, V. J. S. Béjar, R. Rebolo and M. R. Zapatero Osorio A&A, 424 3 (2004) 857-872 Published online: 06 September 2004 DOI: 10.1051/0004-6361:20047048