Warm molecular hydrogen and ionized neon in the HH 2 outflow.
LEFLOCH B., CERNICHARO J., CABRIT S., NORIEGA-CRESPO A., MORO-MARTIN A. and CESARSKY D.
Abstract (from CDS):
We report on spectro-imaging observations of the Herbig-Haro 2 outflow with the ISOCAM camera on board the Infrared Space Observatory. The [Ne II] 12.81 µm and [Ne III] 15.55 µm lines are detected only toward the jet working surface (HH 2H), consistent with the high excitation of this knot in the optical range, while H2pure rotational emission is found all over the shocked region HH 2. The low-energy transition S(2) traces warm gas (T∼400 K) peaked toward knots E and F and extended ejecta (T∼250-380 K) with masses of a few times 10–3 M☉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–1). The higher transitions S(3)-S(7) trace the emission of hot shocked gas (T=1000-1400 K) from individual optical knots in the HH 2 region. The ortho-to-para (OTP) ratio exhibits large spatial variations between 1.2 (knot E) and 2.5 (knot 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 Vs=20-30 km.s–1 propagating into a medium of density ni=104-105 cm–3 with an initial OTP ratio close to 1 in the preshock gas. In the leading edge of the jet, where the geometry of the emission allows a simple modeling, a good agreement is found with velocities derived from the optical proper motions measured in the ionized gas.