The solar carbon, nitrogen, and oxygen abundances from a 3D LTE analysis of molecular lines

Abstract

Carbon, nitrogen, and oxygen are the fourth, sixth, and third most abundant elements in the Sun. Their abundances remain hotly debated due to the so-called solar modelling problem that has persisted for almost $20$ years. We revisit this issue by presenting a homogeneous analysis of $408$ molecular lines across $12$ diagnostic groups, observed in the solar intensity spectrum. Using a realistic 3D radiative-hydrodynamic model solar photosphere and LTE (local thermodynamic equilibrium) line formation, we find $\log {\epsilon }_C=8.47\pm 0.02$, $\log {\epsilon }_N=7.89\pm 0.04$, and $\log {\epsilon }_O=8.70\pm 0.04$. The stipulated uncertainties mainly reflect the sensitivity of the results to the model atmosphere; this sensitivity is correlated between the different diagnostic groups, which all agree with the mean result to within $0.03$ dex. For carbon and oxygen, the molecular results are in excellent agreement with our 3D non-LTE analyses of atomic lines. For nitrogen, however, the molecular indicators give a $0.12$ dex larger abundance than the atomic indicators, and our best estimate of the solar nitrogen abundance is given by the mean: $7.83$ dex. The solar oxygen abundance advocated here is close to our earlier determination of $8.69$ dex, and so the present results do not significantly alleviate the solar modelling problem.

12 pages, 6 figures, 3 tables; accepted for publication in Astronomy & Astrophysics

References in corpus (15)

• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• The chemical make-up of the Sun: A 2020 vision
• Helioseismology and Solar Abundances
• CH in stellar atmospheres: an extensive linelist
• The elemental composition of the Sun II. The iron group elements Sc to Ni
• The elemental composition of the Sun I. The intermediate mass elements Na to Ca
• The elemental composition of the Sun III. The heavy elements Cu to Th
• On the opacity change required to compensate for the revised solar composition
• The GALAH Survey: Non-LTE departure coefficients for large spectroscopic surveys
• Solar oxygen abundance
• Line formation in solar granulation VII. CO lines and the solar C and O isotopic abundances
• On the solar nickel and oxygen abundances
• 3D non-LTE line formation of neutral carbon in the Sun
• The photospheric solar oxygen project: III. Investigation of the centre-to-limb variation of the 630nm [OI]-NiI blend
• Extended theoretical transition data in C I - IV