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Open Access item Warm Molecular Hydrogen and Ionized Neon in the HH2 Outflow

Authors:Moro-Martin, A.
Noriega-Crespo, A.
Cesarsky, D.
Cabrit, S.
Cernicharo, José
Lefloch, Bertrand
Keywords:Stars: formation, ISM: Herbig‐Haro objects, ISM: individual (HH 1–2), ISM: jets and outflows, ISM: molecules
Issue Date:7-May-2003
Publisher:American Astronomical Society
The Astrophysical Journal Letters, 590:L41–L44, 2003 June 10
Abstract:We report on spectro-imaging observations of the Herbig-Haro 2 outflow with the ISOCAM camera onboard the Infrared Space Observatory (ISO). The [Ne II}] 12.81 microns and [Ne III]15.55 microns lines are detected only towards the jet working surface (HH 2H), consistent with the high excitation of this knot in the optical range, while H2 pure rotational emission is found all over the shocked region HH 2. The low energy transition S(2) traces warm gas (T approx. 400K) peaked towards knots E-F and extended ejecta (T approx. 250-380) with masses of a few 0.001 solar mass in the high-velocity CO outflow extending between the powering source and HH 2. Such emission could arise from low-velocity C-type shocks (v= 10-15 km/s). The higher transitions S(3)-S(7) trace the emission of hot shocked gas (T= 1000-1400K) from individual optical knots in the HH 2 region. The ortho to para (OTP) ratio exhibits large spatial variations between 1.2 (E) and 2.5 (H), well below its value at LTE. The emission of the S(3)-S(7) lines is well accounted for by planar C-shock models with a typical velocity V= 20-30 km/s propagating into a medium of density 10^4-10^5 cm-3 with an initial OTP ratio close to 1 in the pre-shock gas. In the leading edge of the jet, where the geometry of the emission allows a simple modelling, a good agreement is found with velocities derived from the optical proper motions measured in the ionized gas.
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