1996A&A...305..582G

Result. are presented on spectroscopic observations of near-infrared molecular hydrogen emission lines towards the Herbig-Haro objects HH 1 and HH 7 to 11. The inferred population densities in the observed H₂ levels towards HH 1 and HH 11 are well described by pure thermal distributions, and single excitation temperatures provide good fits. None of the levels have a significantly enhanced population density as should occur if non-thermal processes were involved. The H₂ emission towards HH 1 arises from collisional excitations in a gas of temperature around 2750K, while contributions from FUV pumping, suggested elsewhere, are not present. The emission from HH 11 arises from gas at similar temperatures, and emission from H₂ re-formation is ruled out. Near-infrared emission of [FeII], present towards HH 1 and HH 7 to 11, is used to infer a reddening of E_B–V≃0.5mag and an electron density of n_e≃5000cm^–3 towards HH 1. Towards individual knots in HH 7 to 11, reddenings range from E_B–V=2 to 7mag. The H₂ and [FeII] observations together suggest the presence of curved J-type shocks, and rule out C-type bow shocks as the origin of the emission.