The study of selected helium lines in the solar spectrum

Level populations of He I in the solar atmosphere (model VAL-C) are calculated by the simultaneous solution of the radiative transfer and statistical equilibrium equations. It is found that the chromosphere in the λ10830 line is an optically thin scattering layer. The dependence of depth of λ10830 on the coronal UV flux illuminating the chromosphere is obtained. The approximate analytical expression for depth and profile of λ10830 as a function of the chromosphere optical thickness in λ10830 is derived. The absolute intensities and profiles of resonance lines λ584, λ537 are also calculated. The results are in reasonable agreement with observational data.