<i>Infrared Space Observatory</i>Spectroscopy of HH 7–11 Flow and Its Redshifted Counterpart

Abstract

We have used the two spectrometers on the iInfrared Space Observatory/i to observe the HH 7-11 flow, its redshifted counterpart, and the candidate exciting source SVS 13 in the star formation region NGC 1333. We detect atomic ([O I] 63 μm, [O I] 145 μm, [Si II] 34.8 μm, [C II] 158 μm) and molecular (Hsup2/sup, CO, Hsup2/supO) lines at various positions along the bipolar flow. Most of the observed lines can be explained in terms of shock-excited emission. In particular, our analysis shows that dissociative (J-type) and nondissociative (C-type) shocks are simultaneously present everywhere along both lobes of the flow. We confirm the low-excitation nature of the Herbig-Haro nebulosities, with shock velocities iVs/i [less than/similar to]40-50 km ssup-1/sup. Toward both lobes of the outflow, we find preshock densities of in/isub0/sub ~ 10sup4/sup cmsup-3/sup for both the J and C components, implying iB/isub0/sub ~ 100 μG for iB/isub0/subαnsub0/subsup0.5/sup. In the central region of the flow, close to the exciting source, the preshock density deduced for the C-shock component is in/isub0/sub ~ 105 cmsup-3/sup, suggesting a magnetic field ~3 times stronger. We propose that the deficiency of gas-phase water in the post-C-shock regions is caused by freezing onto warm grains processed through the J-shock front and traveling along the magnetic field lines. The total observed cooling from the dissociative shock components is consistent with the power lost by a slow molecular outflow accelerated by a fast neutral HI wind. Finally, the skin of the cloud seen in projection toward the flow appears to be weakly photoionized by BD +30°549, the dominant illuminating source of the NGC 1333 reflection nebula.