Contribution and Properties of the Green- and Red-Line Coronal Loops in the K-Corona

A set of high-resolution images of corona obtained during the total solar eclipse on 1991 July 11, was carefully analyzed to investigate the properties of the loop structures observed in the green (530.3 nm) and red (637.4 nm) emission lines and in the continuum. With the help of a structure-enhancement algorithm, we have quantitatively shown that: (1) The green- and red-line loops are quite separately distributed in space. (2) For most structures seen in the continuum in the active-region corona, components can be identified in the green or red line. (3) In the innermost corona, structures in the red-line tend to contribute more to the total column density than the green-line structures. We present two schematic models to explain the spatial relation of the green-line, the red-line, and the continuum loops. Next, we studied individual loops in the green and red lines, and derive that their electron densities are almost the same. We also propose a method to determine the ‘background contribution’ of the green and red lines to the total column density derived from the continuum intensity. It is found that the total column density in the analyzed region can be reasonably explained by a mixture of the 530.3 nm component with a line-of-sight length comparable to the size of the active region, and the 637.4 nm component, which tends to concentrate in loop structures. We thereby conclude that the observed corona is well explained by a plasma of temperatures ranging from 2 MK to 1 MK.