EDP Sciences
Free access
Volume 393, Number 3, October III 2002
Page(s) 1035 - 1051
Section Diffuse matter in space
DOI http://dx.doi.org/10.1051/0004-6361:20021062

A&A 393, 1035-1051 (2002)
DOI: 10.1051/0004-6361:20021062

1-2.5 $\mu$m spectra of jets from young stars: Strong $\ion{Fe}{ii}$ emission in HH111, HH240-241 and HH120

B. Nisini, A. Caratti o Garatti, T. Giannini and D. Lorenzetti

INAF-Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone, Italy
    e-mail: bruni,caratti,teresa,dloren@mporzio.astro.it

(Received 4 June 2002 / Accepted 19 July 2002)

As part of a 1-2.5 $\mu$m spectroscopic survey of jets and molecular outflows, we present the spectra of three Herbig Haro chains (HH111, HH240/241, HH120) characterized by strong emission from several $\ion{Fe}{ii}$ transitions originating from the first 13 fine structure levels. Such emission is correlated with optical $\ion{S}{ii}$ emission and appears to decrease moving away from the driving source. From the analysis of the $\ion{Fe}{ii}$ lines we have derived electron densities values in the range $3\times 10^3$- $2\times 10^4$ cm -3, which are systematically larger than those inferred from optical $\ion{S}{ii}$ line ratios. We suggest that $\ion{Fe}{ii}$ lines, having critical densities higher than the optical $\ion{S}{ii}$ transitions, trace either regions of the post-shock cooling layers with higher compression, or a section of the jet axis at a higher degree of ionization. Strong H 2 emission lines are also detected along the three flows and their analysis indicates that a combination of different shocks can be responsible for their excitation in the different objects. Consequently the $\ion{Fe}{ii}$ line emission, which requires the presence of fast dissociative shocks, is completely independent from the excitation mechanism giving rise to the molecular emission. In addition to the $\ion{Fe}{ii}$ and H 2 lines, emission from other species such as $\ion{C}{i}$, $\ion{S}{ii}$, $\ion{N}{i}$ as well as recombination lines from the Paschen series are detected and have been used as a reference to infer the gas-phase iron abundance in the observed HH objects. We estimate a grain destruction efficiency of about 30-60%: the highest value is found for HH240A, which also shows the highest degree of excitation among the observed objects.

Key words: stars: circumstellar matter -- infrared: ISM -- ISM: Herbig-Haro objects -- ISM: jets and outflows

Offprint request: B. Nisini, bruni@mporzio.astro.it

© ESO 2002

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