CO observations towards bright-rimmed clouds

Abstract

Bright-rimmed clouds (BRCs) appear to be sites of triggered star formation induced through the propagation of shocks initiated by the expansion of nearby H ii regions. Our main aim is to establish support for observations of star-forming activity within a sample of BRCs. A secondary aim is to establish a plausible link between such star formation and observed external influences. We have conducted CO (J = 2–1) observations using the James Clerk Maxwell Telescope to probe the environments of a sample of star-forming BRCs associated with embedded protostellar cores. Local thermodynamic equilibrium analysis allows the determination of the physical properties of these protostars and investigation of the structure and kinematic motions within the molecular gas. Using a combination of archival radio and mid-infrared data, and submillimeter observations, we have refined the Sugitani, Fukui and Ogura (SFO) catalogue, excluding 18 BRCs that do not show any evidence of photoionization induced collapse. Of the remaining 26 clouds that are being photoionized, we find 20 that are associated with embedded protostars. These 20 clouds are excellent candidates with which to further investigate the radiatively driven implosion mode of triggered star formation. Comparing the physical parameters of the triggered and untriggered samples, we find that the surface temperatures of the potentially triggered clouds are significantly higher (by ∼10 K) than those in which triggering is considered unlikely. The higher surface temperatures found towards the sample of potentially triggered clouds are consistent with the hypothesis that these clouds are being externally heated through their exposure to the H ii region.