2004A&A...419..999G

The complete near infrared (0.9-2.5µm) spectra in three different star forming regions (HH24-26, HH72 and BHR71) are presented and analyzed in the framework of shock excitation models. The spectra are dominated by H₂ rovibrational emission (vibrational state ν≤5, excitation energy T_ex≤35000K), while emission from ionized material, recognizable from [Fe II] and [S II] lines, is significantly fainter. The analysis of the H₂ excitation diagrams points to the existence of two different excitation regimes: whilst condensations observed only in the infrared appear to have temperatures rarely exceeding 3000K and can be modelled in the framework of steady-state C-shock models, the infrared counterparts of Herbig Haro (HH) objects exhibit a temperature stratification with components up to more than 5000K. The H₂ emission from representative HH objects (HH26A, HH72A and HH320A) has been successfully modelled by planar J-shocks with magnetic precursors, for which the main parameters (pre-shock density, speed) are derived. However, these same models are unable to reproduce the observed atomic and ionic emission, which probably arises from a distinct and perhaps more embedded region with respect to that traced by the H₂. Some of the physical parameters of such regions (fractional ionization, density) have been estimated in HH72, on the basis of the observed ionic lines.