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 ) , 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 .