Star formation in clusters: early sub-clustering in the Serpens core
  We present high resolution interferometric and single dish observations of molecular gas in the Serpens cluster-forming core. Star formation does not appear to be homogeneous throughout the core, but is localised in spatially- and kinematically-separated sub-clusters. The stellar (or proto-stellar) density in each of the sub-clusters is much higher than the mean for the entire Serpens cluster. This is the first observational evidence for the hierarchical fragmentation of proto-cluster cores suggested by cluster formation models. 
L. Testi (Arcetri), A.I. Sargent (Caltech), L. Olmi (LMT & FCRAO),   J.S. Onello (Cortland)