EDP Sciences
Free Access
Volume 380, Number 2, December III 2001
Page(s) 645 - 664
Section Stellar atmospheres
DOI https://doi.org/10.1051/0004-6361:20011479

A&A 380, 645-664 (2001)
DOI: 10.1051/0004-6361:20011479

Kinetic equilibrium of iron in the atmospheres of cool dwarf stars

II. Weak Fe I lines in the solar spectrum
T. Gehren1, A. J. Korn1 and J. Shi1, 2

1  Institut für Astronomie und Astrophysik der Universität München, München, Germany Universitäts-Sternwarte München (USM), Scheinerstr. 1, 81679 München, Germany
2  National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, PR China

(Received 22 August 2001 / Accepted 18 October 2001)

NLTE line formation calculations of FeI in the solar atmosphere are extended to include weak lines in the visual spectrum of the Sun. Previously established atomic models are used to discriminate between different ways of treating collisional interaction processes. As indicated by the analysis of strong FeI lines, the influence of deviations from LTE in the solar atmosphere on the Fe abundance is small for all lines. To derive a common solar FeI abundance from both strong and weak lines fine-tuning of the microturbulence velocity parameter and the van der Waals damping constants is required. The solar FeI abundances based on all available f-values are dominated by the large scatter already found for the stronger lines. In particular the bulk of the data from the work of May et al. and O'Brian et al. is not adequate for accurate abundance work. Based on f-values measured by the Hannover and Oxford groups alone, the FeI LTE abundances are $\log\varepsilon_{\rm {\ion{Fe}{i},\odot}} = 7.57$ for the empirical and $\log\varepsilon_{\rm {\ion{Fe}{i},\odot}} = 7.48 \ldots 7.51$ for the line-blanketed solar model. The solar Fe ionization equilibrium obtained for different atomic and atmospheric models rules out NLTE atomic models with a low efficiency of hydrogen collisions. At variance with Paper I, it is now in better agreement with laboratory FeII f-values for all types of line-blanketed models. Our final model assumptions consistent with a single unique solar Fe abundance $\log\varepsilon_{\rm {Fe,\odot}} \sim 7.48 \ldots 7.51$ calculated from NLTE line formation are (a) a line-blanketed solar model atmosphere, (b) an iron model atom with hydrogen collision rates $0.5 < S_{\rm H}< 5$ times the standard value to compensate for the large photoionization cross-sections, (c) a microturbulence velocity $\xi_{\rm t}= 1.0$ km s-1, (d) van der Waals damping parameters decreased by $\Delta\log C_6 = -0.10 \ldots -0.15$ as compared to Anstee & O'Mara's calculations, depending on $S_{\rm H}$, (e) FeII f-values as published by Schnabel et al., and (f) FeI f-values published by the Hannover and Oxford groups.

Key words: line: formation -- line: profiles -- Sun: photosphere -- Sun: abundances

Offprint request: T. Gehren, gehren@usm.uni-muenchen.de

© ESO 2001

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