On some aspects of XUV spectroheliograms

Abstract

A comparison between XUV and Ca-K spectroheliograms for 9 dates from 1963 to 1967 showed an excellent correlation between plage intensities in Ca-K and He II 304 Å, except for plages near the limb and a few others. Around the limb all but the highest ionization XUV emission lines form a bright ring, usually weaker over the poles. This is an unresolved combination of the limb-brightened emission from the quiet corona and high chromosphere, and emission extending into the corona above plages located as much as several days from limb passage.In Fe XV and XVI only the localized coronal emissions are observed; these vary in form and intensity from line to line. The 171–500 Å and white-light coronas, recorded on November 12, 1966, correlate well at low altitudes, but beyond 3′ the XUV corona becomes diffuse and without structure.