A census of very-low-mass stars and brown dwarfs in the σ Orionis clusterN. Lodieu, M. R. Zapatero Osorio, R. Rebolo, E. L. Martín and N. C. HamblyA&A, 505 3 (2009) 1115-1127DOI: https://doi.org/10.1051/0004-6361/200911966
