A VLT/FLAMES survey for massive binaries in Westerlund 1 - II. Dynamical constraints on magnetar progenitor masses from the eclipsing binary W13B. W. Ritchie, J. S. Clark, I. Negueruela and N. LangerA&A, 520 (2010) A48DOI: https://doi.org/10.1051/0004-6361/201014834