Empirical Determination of Einstein A-coefficient Ratios of Bright [Fe II] Lines
Journal
Date Issued
2015
Author(s)
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Lorenzetti, D.
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Description
We kindly thank A. Hibbert for providing the Deb Hibbert ( 2011 ) list of A -coefficients of Fe + lines. The ESO staff is acknowledged for support with the observations and the X-shooter pipeline. Financial support from INAF, under PRIN2013 program “Disks, jets and the dawn of planets” is also acknowledged.
Abstract
The Einstein spontaneous rates (A-coefficients) of Fe+ lines have been computed by several authors with results that differ from each other by up to 40%. Consequently, models for line emissivities suffer from uncertainties that in turn affect the determination of the physical conditions at the base of line excitation. We provide an empirical determination of the A-coefficient ratios of bright [Fe II] lines that would represent both a valid benchmark for theoretical computations and a reference for the physical interpretation of the observed lines. With the ESO-Very Large Telescope X-shooter instrument between 3000 Å and 24700 Å, we obtained a spectrum of the bright Herbig-Haro object HH 1. We detect around 100 [Fe II] lines, some of which with a signal-to-noise ratios >=100. Among these latter lines, we selected those emitted by the same level, whose dereddened intensity ratios are direct functions of the Einstein A-coefficient ratios. From the same X-shooter spectrum, we got an accurate estimate of the extinction toward HH 1 through intensity ratios of atomic species, H I recombination lines and H2 ro-vibrational transitions. We provide seven reliable A-coefficient ratios between bright [Fe II] lines, which are compared with the literature determinations. In particular, the A-coefficient ratios involving the brightest near-infrared lines (λ12570/λ16440 and λ13209/λ16440) are in better agreement with the predictions by the Quinet et al. relativistic Hartree-Fock model. However, none of the theoretical models predict A-coefficient ratios in agreement with all of our determinations. We also show that literature data of near-infrared intensity ratios better agree with our determinations than with theoretical expectations.
Based on observations collected with X-shooter at the Very Large Telescope on Cerro Paranal (Chile), operated by the European Southern Observatory (ESO). Program ID: 092.C-0058(A).
Volume
798
Issue
1
Start page
33
Issn Identifier
0004-637X
Ads BibCode
2015ApJ...798...33G
Rights
open.access
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