The morphology of clumps in molecular clouds excited by radiation from HH objects

We have investigated the influence of the radiation field from a Herbig-Har o object on a spherical clump, as the HH object passes by the clump. We hav e included a limited chemistry, and show column density maps of HCO+ and NH 3 to represent the morphology of the predicted emission regions. The morpho logy is sensitive both to the orientation of the line of sight with respect to the HH trajectory and the clump, and to the extinction of the clump. Em ission regions may appear barlike, are-like, or clump-like. The fractional abundances within these structures are observationally significant. However , the clump is not significantly heated by the radiation, and no clump evap oration occurs during the passage of the HH object for cases where the traj ectory does not impact on the clump.