Infrared Space Observatory spectroscopy of HH 7–11 flow and its redshifted counterpart

Molinari, Sergio; Noriega‐Crespo, Alberto; Ceccarelli, Cecilia; Nisini, Brunella; Giannini,, Teresa; Lorenzetti, Dario; Caux, Emmanuel; Liseau, Rene; Saraceno, Paolo and White, Glenn J. (2000). Infrared Space Observatory spectroscopy of HH 7–11 flow and its redshifted counterpart. The Astrophysical Journal, 538(2) pp. 698–709.

DOI: https://doi.org/10.1086/309161

Abstract

We have used the two spectrometers on the Infrared Space Observatory 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 (H2, CO, H2O) 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 Vs [less than/similar to]40-50 km s-1. Toward both lobes of the outflow, we find preshock densities of n0 ~ 104 cm-3 for both the J and C components, implying B0 ~ 100 μG for B0αn00.5. In the central region of the flow, close to the exciting source, the preshock density deduced for the C-shock component is n0 ~ 105 cm-3, 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.

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