Structural Properties of Massive Young Clusters

We have retrieved multicolor WFPC2/HST data from the STScI archive for 27nearby Massive (>= 3x10^4 M_Sun) Young (< 20 Myr) star Clusters (MYCs). Thedata represents the most-complete-to-date sample of clearly resolved MYCs. Wehave analyzed their structural properties and have found that they can beclassified as either Super Star Clusters (SSCs) or as Scaled OB Associations(SOBAs). SSCs have a compact core possibly surrounded by a halo while SOBAshave no core. A morphological sequence can be established from SSCs with weakhalos to SSCs with strong halos to SOBAs and we propose that this is linked tothe original mass distribution of the parent giant molecular clouds. Ourresults indicate that a significant fraction of the stars in MYCs dissipate ontimescales of 10 Gyr or less due to the extended character of some of theclusters. Also, SSCs with ages < 7 Myr have smaller cores on average than thosewith ages > 7 Myr, confirming predictions of numerical simulations with massloss.