Atomic radiative data for oxygen and nitrogen for solar photospheric studies

Abstract

Aims. Our recent reanalysis 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. Methods. Critical to the determination of chemical abundances is the accuracy of the atomic data, especially 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. Results. Our calculations of f values are based on a multi-method, multi-code approach and they are the most detailed and extensive of its kind for the spectral lines of interest. We also report in this paper the details of an extensive R-matrix calculation of photoionization cross sections for oxygen. Conclusions. 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 photoionization cross sections on the spectroscopic estimate of the solar O abundance, using data from different sources. We confirm that our 3D non-LTE value is robust and unaffected by the choice of photoionization data, contrary to the recent claim made by Nahar.