Dynamical mass of the O-type supergiant in ζ Orionis A C. A. Hummel, Th. Rivinius, M.-F. Nieva, O. Stahl, G. van Belle and R. T. Zavala A&A, 554 (2013) A52 Published online: 04 June 2013 DOI: 10.1051/0004-6361/201321434