Clues to the mode of excitation of Fe X ions in the solar corona from the 1980 eclipse observations

Abstract

The line and continuum intensities deduced from the multislit spectra of the (Fe X) coronal emission line taken at the 1980 eclipse are used to discuss the relative roles of radiative and collisional-excitation mechanisms. It is shown that for radii less than 1.2 solar radius, collisional excitation is the predominant mode. Collisional as well as radiative excitation is equally important for radii of 1.2-1.4 solar radius, whereas beyond 1.4 solar radius radiative excitation becomes dominant. The line-width measurements indicate that a large number of locations have half-widths around 1.3 A. The maximum half-width is reached at about 1.4 solar radius with an average value of 1.6 A.