Astronomy and Astrophysics – Astrophysics
Scientific paper
2003-10-16
Astrophys.Space Sci. 292 (2004) 539-545; Astron.Astrophys. 410 (2003) 155-164
Astronomy and Astrophysics
Astrophysics
11 pages, 8 figures
Scientific paper
10.1023/B:ASTR.0000045060.19590.
We investigate the emissivity properties of the main near-IR transitions of the Fe+ ion in the conditions prevailing in the inner regions of jets from young stars, based on a simplified 16-level atom model. We present new diagnostic diagrams involving prominent near-IR line ratios that allow us to constrain the electronic density, temperature, and Fe gas phase abundance ratio, independently of the heating process. Comparison with recent near-IR observations of a sample of HH objects indicates gas phase Fe abundances ranging from 15-50 % up to 100 % of the solar value in agreement with the moderate depletions previously derived from optical line ratios or shock models. Hence, it appears that Fe-bearing dust is efficiently destroyed in stellar jets. We then use our Fe+ emissivity model to predict near-IR [Fe II] emission maps for self-similar, cold MHD disk wind models. We show that observations in [Fe II] with AMBER on the VLTI could severely constrain the MHD solution and the inner launch radius of the jet. We also compare theoretical predictions with recent observations in the near-IR [Fe II] lines of the L1551-IRS5 and DG Tau jets. The cold disk wind model reproduces quite well the two velocity components observed at -100 and -300 km/s, although the high velocity component appears overestimated by a factor of 1.5 in the DG Tau jet. However, the model predicts too little emission at intermediate-velocity and insufficient densities. Denser disk winds with stronger heating at the jet base, which have been invoked for optical jets, also appear needed in younger, embedded Class I jet sources.
Cabrit Silvie
Dougados Catherine
Ferreira Jonathan
Garcia Paulo
O'Brien Darren
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