Optical polarimetric observations of the microquasar LS 5039 J. A. Combi, S. A. Cellone, J. Martí, M. Ribó, I. F. Mirabel and J. Casares A&A, 427 3 (2004) 959-963 Published online: 16 November 2004 DOI: 10.1051/0004-6361:20041433