Inelastic O+H collisions and the O I 777 nm solar centre-to-limb variation

The O I 777 nm triplet is a key diagnostic of oxygen abundances in the atmospheres of FGK-type stars; however, it is sensitive to departures from local thermodynamic equilibrium (LTE). The accuracy of non-LTE line formation calculations has hitherto been limited by errors in the inelastic O+H collis...

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Bibliographic Details
Published in:Astronomy and astrophysics (Berlin) 2018-08, Vol.616, p.A89
Main Authors: Amarsi, A. M., Barklem, P. S., Asplund, M., Collet, R., Zatsarinny, O.
Format: Article
Language:English
Subjects:
atomic data
Calibration
Coefficients
Diagnostic systems
line: formation
Local thermodynamic equilibrium
Mathematical models
methods: numerical
Oxygen
radiative transfer
Solar atmosphere
Stellar atmospheres
Sun: abundances
Sun: atmosphere
Three dimensional models
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Summary:The O I 777 nm triplet is a key diagnostic of oxygen abundances in the atmospheres of FGK-type stars; however, it is sensitive to departures from local thermodynamic equilibrium (LTE). The accuracy of non-LTE line formation calculations has hitherto been limited by errors in the inelastic O+H collisional rate coefficients; several recent studies have used the Drawin recipe, albeit with a correction factor SH that is calibrated to the solar centre-to-limb variation of the triplet. We present a new model oxygen atom that incorporates inelastic O+H collisional rate coefficients using an asymptotic two-electron model based on linear combinations of atomic orbitals, combined with a free electron model based on the impulse approximation. Using a 3D hydrodynamic STAGGER model solar atmosphere and 3D non-LTE line formation calculations, we demonstrate that this physically motivated approach is able to reproduce the solar centre-to-limb variation of the triplet to 0.02 dex, without any calibration of the inelastic collisional rate coefficients or other free parameters. We infer log ϵO = 8.69 ± 0.03 from the triplet alone, strengthening the case for a low solar oxygen abundance.
ISSN:0004-6361
1432-0746
DOI:10.1051/0004-6361/201832770