EPoS Contribution

The Chandra View of Triggered Star Formation in Bright Rimmed Clouds

Konstantin Getman
Pennsylvania State University, University Park, USA
The formation of many stars in the Galaxy appears to be triggered by external compression processes such as OB ionization, winds, or supernovae shocks. However, quantitative understanding of triggering processes is still primitive. Radiation driven implosion (RDI) is currently considered as the most observationally testable model using bright rimmed clouds (BRCs) on the edges of large HII regions. We have made several Chandra X-ray observations combined with IR, optical, and CO surveys to elucidate the mechanism, efficiency, and stellar populations produced by small-scale triggered star formation (TSF) around HII regions. Along with the many observational features of the RDI mechanism, such as the presence of an exciting star and a BRC surrounded by an ionized rim facing the cloud, dense molecular core(s) close to the rim, high molecular gas excitation and turbulence, we often discover spatio-temporal gradients of young stars from BRCs towards primary ionizing stars. We find that the RDI process generally propagates at velocities near 1 km/s, persists over several million years, and produces a few dozen to a few hundred stars in/around 1-4 pc diameter molecular globules. For the large nearby HII region IC 1396, we estimate that the TSF contribution to the stellar population of the entire HII region exceeds 13-20% today. Such triggering on the periphery of HII regions may be a significant mode of star formation in the Galaxy.
E. Feigelson, PSU, USA
A. Sicilia-Aguilar, UAM, Spain
P. Broos, PSU, USA
M. Kuhn, PSU, USA
G. Garmire, PSU, USA