A simulation of an HH jet in a molecular environment.

The heads of some Herbig-Haro (HH) jets have recently been detected in emission lines of molecular species such as H_2_ and CO. In this paper we present an axisymmetric numerical simulation of an atomic, nonadiabatic jet moving into a molecular environment, from which predictions of intensity maps in atomic/ionic and molecular emission lines can be carried out. While the maps predicted from these models for emission lines of atoms and ions have the expected bow-shaped structure, the maps for H_2_ lines have a "hole" in the stagnation region of the bowshock, where the molecules are dissociated. The morphology predicted for the molecular emission intensity maps is in clear qualitative agreement with recent observational results. We also present predictions of position-velocity diagrams, which will be useful for comparisons with future long-slit spectroscopic observations of HH objects.