The mass of the neutron star in Vela X-1 O. Barziv, L. Kaper, M. H. Van Kerkwijk, J. H. Telting and J. Van Paradijs A&A, 377 3 (2001) 925-944 Published online: 15 October 2001 DOI: 10.1051/0004-6361:20011122