Atomic Radiative Data for Oxygen and Nitrogen for Solar Photospheric Studies

Abstract

Our recent re-analysis of the solar photospheric spectra with non-local thermodynamic equilibrium (non-LTE) models resulted in higher metal abundances compared to previous works. When applying the new chemical abundances to Standard Solar Model calculations, the new composition resolves the long-standing discrepancies with independent constraints on the solar structure from helioseismology. Critical to the determination of chemical abundances is the accuracy of the atomic data, specially the $f$-values, used in the radiative transfer models. Here we describe in detail the calculations of $f$-values for neutral oxygen and nitrogen used in our non-LTE models. Our calculations of $f$-values are based on a multi-method, multi-code approach and are the most detailed and extensive of its kind for the spectral lines of interest. We also report in this paper the details of extensive R-matrix calculation of photo-ionization cross sections for oxygen. Our calculation resulted in reliable $f$-values with well constrained uncertainties. We compare our results with previous theoretical and experimental determinations {of atomic data. We also quantify the influence of adopted photo-ionisation cross-sections on the spectroscopic estimate of the solar O abundance, using the data from different sources. We confirm that our 3D non-LTE value is robust and unaffected by the choice of photo-ionisation data, contrary to the recent claim made by Nahar.