Star-forming galaxies in SDSS: signs of metallicity evolution M. A. Lara-López, J. Cepa, A. Bongiovanni, H. Castañeda, A. M. Pérez García, M. Fernández Lorenzo, M. Póvic and M. Sánchez-Portal A&A, 493 1 (2009) L5-L8 Published online: 27 November 2008 DOI: 10.1051/0004-6361:200811033