On the excitation of the infrared knots along protostellar jets ^*,**

¹ INAF-Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone, Italy
² Physics Department, The University, Durham DH1 3LE, UK
³ Università degli Studi “Tor Vergata”, via della Ricerca Scientifica 1, 00133 Roma, Italy

Corresponding author: T. Giannini, teresa@coma.mporzio.astro.it

Received: 16 July 2003
Accepted: 27 February 2004

Abstract

The complete near infrared (0.9–2.5 μm) 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 , excitation energy  K), 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 3000 K 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 5000 K. 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.