INFRARED-SPECTROSCOPY OF HERBIG-HARO OBJECTS

We report near-infrared spectrophotometry of H-2 emission in a set of low-excitation Herbig-Haro objects for which optical emission line fluxes are available. In most objects, the H-2 line ratio 2-1 S(3)/1-0 S(1) is consistent with collisional excitation in low-velocity shocks, with no indication of a fluorescence component. The excitation plot for HH 43 shows definite curvature, with a nonlinear (logarithmic) best fit suggesting that the higher excitation lines are created in the hottest postshock gas. This curvature of the excitation plot is akin to that seen in HH 98A and the OMC, where it has been taken as evidence of nondissociative J-shocks. In general, the 1-0 S(1) flux appears to be comparable to the H alpha flux. The implications of this are discussed with respect to the nature of the shocks which produce the optical and H-2 emission.