The metallicity gradient of M 33: chemical abundances of H ii regions L. Magrini, J. M. Vílchez, A. Mampaso, R. L. M. Corradi and P. Leisy A&A, 470 3 (2007) 865-874 Published online: 25 May 2007 DOI: 10.1051/0004-6361:20077445