Chemical abundances of late-type pre-main sequence stars in the σ Orionis cluster J. I. González Hernández, J. A. Caballero, R. Rebolo, V. J. S. Béjar, D. Barrado y Navascués, E. L. Martín and M. R. Zapatero Osorio A&A, 490 3 (2008) 1135-1142 Published online: 17 September 2008 DOI: 10.1051/0004-6361:200810398