On coronal Fe abundances and temperatures from XUV emission lines

Data obtained by the OSO-7 spectroheliograph on strong XUV lines of five different Fe ions from the outer equatorial corona are presented. Interpretation of the data with a spherically symmetric model atmosphere gives average ion abundances for lines of sight at 0.3 solar radii from the limb. Fe XVI is usually more abundant than Fe XV, XIV, XII and IX, but there are times when Fe XII is more abundant than the other ions. The deviation of measured relative abundances of Fe XII, XIV, and XVI from predictions of ionization equilibrium at one temperature seems to indicate that there are appreciable temperature variations along lines of sight. Element abundances are very uncertain since they appear to depend so heavily on likely but unknown density irregularities along lines of sight. (Auth.)