The 3D non-LTE solar nitrogen abundance from atomic lines

¹ Theoretical Astrophysics, Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden
e-mail: anish.amarsi@physics.uu.se
² Centre Spatial de Liège, Université de Liége, avenue Pré Aily, 4031 Angleur-Liège, Belgium
³ Space sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège, Allée du 6 août, 17 B5C, 4000 Liège, Belgium
⁴ Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2600, Australia
⁵ Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark

Received: 5 March 2020
Accepted: 27 March 2020

Abstract

Nitrogen is an important element in various fields of stellar and Galactic astronomy, and the solar nitrogen abundance is crucial as a yardstick for comparing different objects in the cosmos. In order to obtain a precise and accurate value for this abundance, we carried out N I line formation calculations in a 3D radiative-hydrodynamic STAGGER model solar atmosphere in full 3D non-local thermodynamic equilibrium (non-LTE). We used a model atom that includes physically motivated descriptions for the inelastic collisions of N I with free electrons and with neutral hydrogen. We selected five N I lines of high excitation energy to study in detail, based on their strengths and on their being relatively free of blends. We found that these lines are slightly strengthened from non-LTE photon losses and from 3D granulation effects, resulting in negative abundance corrections of around − 0.01 dex and − 0.04 dex, respectively. Our advocated solar nitrogen abundance is log ɛ_N = 7.77, with the systematic 1σ uncertainty estimated to be 0.05 dex. This result is consistent with earlier studies after correcting for differences in line selections and equivalent widths.