Poster abstract

Starburst clusters are well known for their high rate of star formation. Around ten starburst clusters are currently known in our galaxy and Westerlund 1 (Wd 1) with its rich population of high-mass stars is the most massive one. Strong winds and ultraviolet radiation from massive stars in the center of Wd1 have cleared away nearby material, giving a chance better to resolve individual cluster members. Very close location of Wd 1 to the galactic plane (b= -0.35°), yields a strong contamination by fore- and background nonmembers. For unbiased determination of the cluster parameters and IMF, we have made a proper motion membership selection, based on 2 epochs NACO/VLT observations with a 5 years time baseline. At the age of 4 Myr, the stars in Wd 1 are only a little affected by dynamical evolution, that's why present-day mass function of Wd 1 is identical with the initial mass function. We discuss physical and dynamical properties of Wd 1 and present a new estimate of the intermediate to low-mass IMF of the cluster.