Varied Mechanisms for Star Formation in Bright-Rimmed Clouds
St Mary's University, Halifax, Canada
Bright-rimmed clouds (BRCs) are potential examples of triggered star-formation regions, in which photoionization driven shocks caused by the expansion of HII regions induce protostellar collapse within the clouds. A sample of optically bright BRCs at the edge of HII regions has been observed at radio, infrared and submillimetre wavelengths, these observations reveal dense cores present within the heads of 44 observed BRCs drawn from a catalogue of IRAS sources embedded within HII regions, supportive of the scenario proposed by radiatively driven implosion (RDI) models. The physical properties of these cores indicate the presence of star formation across the majority of our sample. This star-formation appears to be predominately in the regime of intermediate to high mass and may indicate the formation of clusters.
A fundamental difference appears to exist between different morphological types of BRC. Morphological variations in BRCs have previously been attributed to an evolutionary scenario of RDI. However, the physical properties of cores found within different types of BRC indicate that the strength of the ambient ionisation field is highly correlated with the attributes of certain cores, and not with others. The suggestion is that different morphological types of BRC have followed different evolutionary pathways, this is supported by the mass distributions of cores associated with the different morphologies.