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Wednesday 09 Feb 2011: Mass segregation and elongation of the starburst cluster Westerlund 1
Mario Gennaro - Max-Planck-Institute for Astronomy, Heidelberg, Germany
Physics, 4th Floor interaction area 11:00-12:00
Westerlund 1 (Wd1) is among the most massive young clusters in the Local Group. I will present an analysis of the properties of Wd1, based on NTT/SofI near-infrared photometry. From comparison with stellar models, we derived an extinction A_Ks = 0.91 +/- 0.05 mag, an age \tau = 4 +/- 0.5 Myr and a distance d = 4.0 +/- 0.2 kpc, as well as a total mass of M_Wd1 =~ 5x10^4 M_sun. Using spatially dependent completeness corrections we performed a 2D study of the cluster's IMF and, in addition, of the stellar density profiles of the cluster as a function of mass. From both IMF slope variations and stellar density, we find strong evidence of mass segregation. For a cluster with some 10^5 stars, this is not expected at such a young age as the result of two-body relaxation alone. We also confirm previous findings on the elongation of Wd1; assuming an elliptical density profile, we found an axis ratio of a:b = 3:2. Rapid mass segregation and elongation could be well explained as the results of subclusters merging during the formation of Westerlund 1.
