Volume 474, Number 3, November II 2007
|Page(s)||941 - 950|
|Section||Interstellar and circumstellar matter|
|Published online||23 October 2007|
Max-Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany e-mail: firstname.lastname@example.org
Accepted: 31 August 2007
Aims.Optical and near-infrared spectroscopy of molecular hydrogen in interstellar shocks provide a very powerful probe of the physical conditions that prevail in interstellar shocks.
Methods.Integral-field spectroscopy of H2 in the optical wavelength region and complementary long-slit near-infrared spectroscopy towards HH91A are used to characterize the ro-vibrational population distribution among H2 levels with excitation energies up to 30 000 cm-1.
Results.The detection of some 200 ro-vibrational lines of molecular hydrogen ranging between 7700 Å and 2.3 μm is reported. Emission lines which arise from vibrational levels up to are detected. The H2 emission arises from thermally excited gas where the bulk of the material is at a temperature of 2750 K and where 1% is at 6000 K. The total column density of shocked molecular hydrogen is N(H2) = 1018 cm-2. Non-thermal excitation scenarios such as UV fluorescence do not contribute to the H2 excitation observed towards HH91A.
Conclusions.The emission of molecular hydrogen towards HH91A is explained in terms of a slow J-shock that propagates into a low-density medium, that has been swept up by previous episodes of outflows that have occurred in the evolved HH90/91 complex.
Key words: ISM: molecules / ISM: Herbig-Haro objects / ISM: jets and outflows
Based on observations collected at the Centro Astronomico Hispano Aleman (CAHA) Calar Alto, operated jointly by the Max-Planck Institute for Astronomy and the Instituto de Astrofisica de Andalucia (CSIC). Based on observations collected at the European Southern Observatory, La Silla, Chile.
© ESO, 2007
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