Assessing molecular line diagnostics of triggered star formation using
  synthetic observations
  We investigate observational signatures of triggered star formation in bright
rimmed clouds (BRCs) by using molecular line transfer calculations based on
radiation-hydrodynamic radiatively-driven-implosion models. We find that for
BRCs the separation in velocity between the line profile peak of an optically
thick and an optically thin line is determined by both the observer viewing
angle and the density of the shell driving into the cloud. In agreement with
observations, we find that most BRC line profiles are symmetric and that
asymmetries can be either red or blue, in contrast to the blue-dominance
expected for a collapsing cloud. Asymmetries in the line profiles arise when an
optically thick line is dominated by the shell and an optically thin line is
dominated by the cloud interior to the shell. The asymmetries are red or blue
depending on whether the shell is moving towards or away from the observer
respectively. Using the known motions of the molecular gas in our models we
rule out the envelope expansion with core collapse mechanism as the cause of
the lack of blue-asymmetry in our simulated observations. We show that the
absence of a strong photon dominated region (PDR) around a BRC may not rule out
the presence of triggered star formation: if the BRC line profile has a strong
blue component then the shell is expected to be driving towards the observer,
suggesting that the cloud is being viewed from behind and the PDR is
obstructed. This could explain why BRCs such as SFO 80, 81 and 86 have a blue
secondary peak and only a weak PDR inferred at 8 microns. Finally we also test
the use of 12CO, 13CO and C18O as diagnostics of cloud mass, temperature and
column density. We find that the inferred conditions are in reasonable
agreement with those from the models.
