The contributions of J-type shocks to the H2 emission from molecular outflow sources |
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Authors: | D R Flower J Le Bourlot G Pineau des Forêts S Cabrit |
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Institution: | Physics Department, The University, Durham DH1 3LE;LUTH, Observatoire de Paris, F-92195 Meudon Cedex, France;IAS, Universitéde Paris-Sud, F-92405 Orsay, France;LERMA, Observatoire de Paris UMR 8540 du CNRS, 61 Avenue de l'Observatoire, F-75014 Paris, France |
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Abstract: | We present the results of modelling of the H2 emission from molecular outflow sources, induced by shock waves propagating in the gas. We emphasize the importance of proper allowance for departures from equilibrium owing to the finite flow velocity of the hot, compressed gas, with special reference to the excitation, dissociation and reformation of H2. The salient features of our computer code are described. The code is applied to interpreting the spectra of the outflow sources Cepheus A West and HH43. Particular attention is paid to determining the cooling times in shocks whose speeds are sufficient for collisional dissociation of H2 to take place; the possible observational consequences of the subsequent reformation of H2 are also examined. Because molecular outflow sources are intrinsically young objects, J-type shocks may be present in conjunction with magnetic precursors, which have a C-type structure. We note that very different physical and dynamical conditions are implied by models of C- and J-type shocks which may appear to fit the same H2 excitation diagram. |
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Keywords: | molecular processes shock waves stars: winds outflows ISM: Herbig–Haro objects ISM: jets and outflows ISM: molecules |
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