NLTE formation of the solar silicon spectrum: Silicon abundance in one-dimensional models of the solar atmosphere

Abstract

NLTE formation of the silicon spectrum is studied in three one-dimensional semiempirical models of the solar atmosphere: HOLMUL, MACKKL, and VAL,C. The NLTE silicon abundance calculated from 65 Si I lines of different strengths is almost independent of the excitation potentials, wavelengths, and equivalent widths if the van der Waals damping constant γ6 is calculated using the Unsold approximation with an enhancement factor E = 1.5. The NLTE silicon abundance range from 7.547 ± 0.012 (HOLMUL) to 7.582 ± 0.013 (VAL,C). The use of the Anstee-Barklem-O’Mara (ABO) theory to calculate γ6 leads to a decrease in the silicon abundance with an increase in the equivalent widths. It is found that the NLTE silicon abundance corrections are, on average, −0.05 dex. The errors in the NTLE abundance due to uncertainties in the cross sections of photoionization and inelastic collisions with electrons and hydrogen atoms are 0.02 dex or less. It is shown that the use of the shifted Gurtovenko-Kostyk “solar” oscillator-strength scale instead of the experimental scale proposed by Becker et al. gives almost the same silicon abundance.