Source Function in a Non-Equilibrium Atmosphere.VI. The Frequency Dependence of the Source Function for Resonance Line.

Abstract

The frequency dependence of the line source function is investigated for the case of pure coherent scattering in the reference frame of the atom. It is shown that the thermal redistribution due to Doppler effect gives a form of scattering similar to complete redistribution in the line core and coherency in the wings. Using a modified form for this redistribution and allowing for some residual non-coherency due to collisions in the frame of the atom, an algebraic solution of the transfer equation is obtained, and emergent line profiles are computed, for an isothermal atmosphere. It is shown that the line shape in the transition region from line core to wing is strongly influenced by the proportion of this residual non-coherency. It is finally suggested that, until the strength of collisional perturbations is better understood from theoretical or laboratory studies, theoretical work on line spectra should adopt complete redistribution in scattering.