Radiation scattering in the solar corona

Abstract

This paper discusses the scattering in the solar corona of the radiation emitted by the solar disk. We obtain expressions for the emissivity which permit to deduce the spectral characteristics of the scattered radiation. With these expressions, assuming a Maxwellian distribution for the velocities of the scattering ions and a simple spectral shape of the exciting radiation, we produce approximate analytic formulae which show some interesting properties of the scattered radiation that do not clearly emerge from the exact expressions. Among them, the expression for the Doppler shift of the radiatively excited component of a line, and that for its width. We also examine the case of bi-Maxwellian velocity distributions and the scattering by the free electrons.