Magnetic field measurements of O stars with FORS 1 at the VLT S. Hubrig, M. Schöller, R. S. Schnerr, J. F. González, R. Ignace and H. F. Henrichs A&A, 490 2 (2008) 793-800 Published online: 11 September 2008 DOI: 10.1051/0004-6361:200810171