Volume 616, August 2018
|Number of page(s)||12|
|Published online||24 August 2018|
Inelastic O+H collisions and the O I 777 nm solar centre-to-limb variation
Max Planck Institute für Astronomy,
2 Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia
3 Theoretical Astrophysics, Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden
4 Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
5 Department of Physics and Astronomy, Drake University, Des Moines, IA 50311, USA
Accepted: 27 March 2018
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.
Key words: atomic data / radiative transfer / line: formation / Sun: atmosphere / Sun: abundances / methods: numerical
© ESO 2018
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