Solving the Excitation and Chemical Abundances in Shocks: The Case of HH 1
Journal
Date Issued
2015
Author(s)
Description
The ESO staff is acknowledged for support with the observations and the X-shooter pipeline. The authors thank J. M. Alcalá for his useful comments and suggestions. S.A. acknowledges support from the T-REX-project, the INAF (Istituto Nazionale di Astrofisica) national project aimed at maximizing the participation of astrophysicists and Italian industries to the realization of the E-ELT (European Extremely Large Telescope). The T-REX project has been approved and funded by the Italian Ministry for Research and University (MIUR) in the framework of the Progetti Premiali 2011 and then Progetti Premiali 2012 Financial support from INAF, under PRIN2013 program “Disks, jets and the dawn of planets” is also acknowledged. L.P. has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement n. 267251. Facility: VLT (X-shooter) .
Abstract
We present deep spectroscopic (3600-24700 Å ) X-shooter observations of the bright Herbig-Haro object HH 1, one of the best laboratories to study the chemical and physical modifications caused by protostellar shocks on the natal cloud. We observe atomic fine structure lines, H i and He i recombination lines and H2 ro-vibrational lines (more than 500 detections in total). Line emission was analyzed by means of Non-local Thermal Equilibiurm codes to derive the electron temperature and density, and for the first time we are able to accurately probe different physical regimes behind a dissociative shock. We find a temperature stratification in the range 4000 K \div 80,000 K, and a significant correlation between temperature and ionization energy. Two density regimes are identified for the ionized gas, a more tenuous, spatially broad component (density ̃103 cm-3), and a more compact component (density ≥slant 105 cm-3) likely associated with the hottest gas. A further neutral component is also evidenced, having a temperature ≲10,000 K and a density >104 cm-3. The gas fractional ionization was estimated by solving the ionization equilibrium equations of atoms detected in different ionization stages. We find that neutral and fully ionized regions co-exist inside the shock. Also, indications in favor of at least partially dissociative shock as the main mechanism for molecular excitation are derived. Chemical abundances are estimated for the majority of the detected species. On average, abundances of non-refractory/refractory elements are lower than solar of about 0.15/0.5 dex. This indicates the presence of dust inside the medium, with a depletion factor of iron of ̃40%. Based on observations collected at the European Southern Observatory, (92.C-0058).
Volume
814
Issue
1
Start page
52
Issn Identifier
0004-637X
Ads BibCode
2015ApJ...814...52G
Rights
open.access
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