Star clusters in the Sh2-132 complex : clues about the connection between embedded and open clusters

Abstract

Embedded clusters are formed in molecular clouds where massive stars can produce HII regions. The detailed evolutionary connection between embedded and open clusters, and the origin of associations are still to be discovered. There appears to be a high infant mortality rate among embedded clusters, and the few survivors evolve to open clusters. We study the colour–magnitude diagrams (CMDs) and structure of the star clusters related to the Sh2-132 H II region using the Two-Micron All-Sky Survey (2MASS) data base. The fundamental and structural parameters of clusters are determined using main-sequence and pre-main-sequence isochrones and stellar radial density profiles. We report on the discovery of four clusters. One of these is projected a few diameters away from the optical cluster, Teutsch 127, and appears to be deeply embedded, seen only in the infrared. Evidence is found that we are witnessing the dynamical transition from an embedded to an open cluster. An additional cluster is also close to Teutsch 127 and might be associated with a bow-shock. We also study the CMD and structure of the open cluster, Berkeley 94, in Sh2-132, and a new cluster that is projected in the outskirts of the complex. Finally, we have searched for star clusters around the two known Wolf–Rayet stars in the complex. One of these appears to be related to a compact cluster. Finally, the present analyses suggest early dynamical evolution for young star clusters.