Molecular line emission in HH54: a coherent view from near to far infrared

摘要

Aims. We present a detailed study of the infrared line emission (1-200micron) in the Herbig-Haro object HH54. Our database comprises: high- (R~9000)and low- (R~600) resolution spectroscopic data in the near-infrared band (1-2.5micron); mid-infrared spectrophotometric images (5-12 micron); and, far-IR(45-200 micron, R~200) spectra acquired with the ISO satellite. As a result, weprovide the detection of and the absolute fluxes for more than 60 molecularfeatures (mainly from H2 in the near- and mid-infrared and from H2O, CO and OHin the far-infrared) and 23 ionic lines. Methods. The H2 lines, coming fromlevels from v=0 to v=4 have been interpreted in the context of a state-of-artshock code, whose output parameters are adopted as input to a Large VelocityGradient computation in order to interpret the FIR emission of CO, H2O and OH.Results. The H2 emission can be interpreted as originating in eithersteady-state J-type shocks or in quasi-steady J-type shocks with magneticprecursor. However, our multi-species analysis shows that only a model of aJ-type shock with magnetic precursor (v_shock=18 km/s, n_H=10^4 cm^-3, B=100microG, age=400 yr) can account for both the observed H2 emission and the COand H2O lines. Such a model predicts a H2O abundance of ~ 7 10^-5, in agreementwith estimations from other shock models for outflows associated with low massprotostars. We can exclude the possibility that the observed atomic lines arisein the same shock as the molecular lines, and give arguments in favour of thepresence of a further high-velocity, fully dissociative shock component in theregion. Finally, in view of the forthcoming spectroscopic facilities on boardof the Herschel satellite, we provide predictions for H2O lines considered tobe the most suitable for diagnostic purposes.