MOLECULAR-HYDROGEN AND EXCITATION IN THE HH-1-2 SYSTEM

We present a series of molecular hydrogen images of the Herbig-Haro 1-2 system in the 1-0 S(1) transition at 2.121 mu m, with a spatial resolution of similar to-2''. The distribution of H-2 is then compared with that of the excitation, given by the [S II] 6717+6731 to H alpha line ratio. We find that most optical condensations in the HH 1-2 system, including the VLA 1 jet, have Hz counterparts. H-2 emission is detected in most low excitation knots, as expected for low velocity shocks (50 km s(-1)<), but also in high excitation regions, like in HH 1F and HH 2A'. For these latter objects, the H-2 emission could be due to the interaction of the preionizing flux, produced by 150-200 km s(-1) shocks, with the surrounding interstellar matter, i.e., fluorescence. The lack fluorescent lines in the UV, however, suggest a different mechanism. H-2 is detected at the tip of the VLA 1 jet, where the knot morphology suggests the presence of a second bow shock. H-2 is detected also SE of HH 2E and SW of HH 1F, in regions with known NH3 emission.