Electrons in the solar corona

Abstract

During the eclipse of 15 February 1961, photometric measurements were obtained for the inner corona till r/R ₀ = 2.5 at Imperia, Italy (Figure 1), and for the outer corona between r/R ₀ = 2.0 and 7.0 at Hvar, Jugoslavia (Plate I). Morphologic pictures of the streamers were taken at Observatoire de Haute-Provence, France, with the technique of the gradient compensation (Plate II). K-coronameter observations were daily recorded at Meudon and Pic-du-Midi Observatories, France, from 9 to 22 February 1961 (Figures 9 and 10).

These combined techniques give accurate localization, shape and photometry of the streamers. Four of them lie near the limb-plane and the mathematical approach of Van de Hulst applies to derive the electron-density repartition within these streamers (Figures 13, 15 and 16a). Compared with the previously published electron-density determinations on 10 corona-streamers (Figure 16b), the new determinations correspond to a particularly large variety of streamers. Local increases of electron-densities are found at the neck of helmet-shaped streamers, with an almost local zero gradient and are discussed.