Models and Observations of the Millimeter and Submillimeter Molecular Line Emission of Bright-Rimmed Clouds

Abstract

We present the results of a comparison of new millimeter and submillimeter molecular line survey of bright-rimmed clouds, observed at FCRAO in the CO (J=1-0), C¹⁸O (J=1-0), HCO⁺ (J=1-0), H¹³CO⁺ (J=1-0), and N₂H⁺(J=1-0) transitions, at the HHT in the CO (J=2-1), HCO⁺ (J=3-2), HCO⁺ (J=4-3), H¹³CO⁺ (J=3-2), and H¹³CO⁺ (J=4-3), and at the CSO in the HCO⁺ (J=4-3) and H¹³CO⁺ (J=4-3) molecular line transitions with synthetic observations of a hydrodynamic shock driven triggered star formation model. We also present observations of three Bok globules done for comparison with the bright-rimmed clouds. We find that the appearance of the millimeter CO and HCO⁺ emission is dominated by the morphology of the shock front in the bright-rimmed clouds. The HCO⁺ (J=1-0) emission tends to trace the swept up gas ridge and overdense regions which may be triggered to collapse as a result of sequential star formation. The morphologies of the observed bright-rimmed cloud are in good agreement with the our modeled emission. Five of the seven bright-rimmed clouds we observe seem to have an outflow, however only one shows the spectral line blue-asymmetric signature that is indicative of infall, in the optically thick emission. We also present evidence that in bright-rimmed clouds the nearby shock front may heat the core from outside-in thereby washing out the normally observed line infall signatures seen in isolated star forming regions. We find that the derived core masses of these bright-rimmed clouds are similar to other low and intermediate mass star forming regions.