An approximate calculation of the effect of opacity in the solar spectral lines of C III

Abstract

In this paper we make use of the fact that the intensity ratio between two spectral lines arising from the same upper level can depend on opacity, to determine the optical thickness of the solar atmosphere to C III radiation. Our analysis is based on observations taken, near the Sun's limb during the Skylab mission, with the Naval Research Laboratory's spectrograph. By introducing the measured abundance of carbon and the results of ionization balance calculations an estimate is made of the line-of-sight physical thickness of the regions emitting C III lines at the disc centre.