Bright-rimmed clouds in IC 1396

Aims . We investigate the dynamical and physical structures of bright-rimmed clouds (BRCs) in a nearby H II region. We focused on carbon- and oxygen-bearing species that trace photon-dominated regions (PDRs) and warm molecular cloud surfaces in order to understand the effect of UV radiation from the exciting stars on the cloud structure. Methods . We mapped four regions around the most prominent BRCs at scales of 4–10 arcmin in the H II region IC 1396 (IC 1396A, B, D, and E) in [C II ] 158 µm with (up)GREAT on board SOFIA. IC 1396 is predominantly excited by an O6.5V star. Toward IC 1396A, we also observed [O I ] 63 µm and 145 µm. We combined these observations with JCMT archive data, which provide the low- J transitions of CO, 13 CO, and C 18 O. All spectra are velocity-resolved. Results . The line profiles in the four mapped regions show a variety of velocity structures, which we investigated in detail for all observed emission lines. IC 1396B and D show clearly distinct velocity components that overlap along the line of sight. We find no clear sign of photoevaporating flows in the [C II ] spectra, although the uncertainty in the location of the BRCs along the line of sight makes this interpretation inconclusive. Our analysis of the [ 13 C II ] emission in IC1396 A, which has the best signal-to-noise ratio, suggests that the [C II ] is likely mostly optically thin. The heating efficiency, measured by the ([C II ]+[O I ] 63 µm)/far-infrared intensity ratio, is higher in the northern part of IC 1396A than in the southern part, which may indicate a difference in the dust properties of the two areas. Conclusions . The complex velocity structures identified in the BRCs of IC 1396, which is apparently a relatively simple H II region, highlight the importance of velocity-resolved data for disentangling different components along the line of sight and thus facilitating a detailed study of the dynamics of the cloud. We also demonstrate that the optically thin [ 13 C II ] and [O I ] 145 µm emission lines are essential for a conclusive interpretation of the [C II ] 158 µm and [O I ] 63 µm line profiles.