  Westerlund 1 is one of the most massive young clusters known in the Local
Group, with an age of 3-5 Myr. It contains an assortment of rare evolved
massive stars, such as blue, yellow and red supergiants, Wolf-Rayet stars, a
luminous blue variable, and a magnetar, as well as 4 massive eclipsing binary
systems (Wddeb, Wd13, Wd36, WR77o, see Bonanos 2007). The eclipsing binaries
present a rare opportunity to constrain evolutionary models of massive stars,
the distance to the cluster and furthermore, to determine a dynamical lower
limit for the mass of a magnetar progenitor. Wddeb, being a detached system, is
of great interest as it allows determination of the masses of 2 of the most
massive unevolved stars in the cluster. We have analyzed spectra of all 4
eclipsing binaries, taken in 2007-2008 with the 6.5 meter Magellan telescope at
Las Campanas Observatory, Chile, and present fundamental parameters (masses,
radii) for their component stars.
