The structure of the monochromatic corona in the surroundings of prominences

Abstract

It is well known that in the immediate surroundings of stationary filaments the white light of the corona is strongly reduced. The same effect is observed in the monochromatic emissions of the lines 5303 and 6374 Å, for which in Figures 1–3 some examples are given. This diminuation of light can only be explained by a corresponding diminuation of the density. As the density in the vicinity of the prominence may be as small as one tenth of that of the undisturbed corona, or even smaller in some cases, these features are called cavities. The intensity distribution of the line 5303 Å in the region of a stable prominence observed on October 6, 1969 has been analysed (Figure 4). The cavity turns out to be of the shape of a half-ellipsoid. Its length (in heliographic longitude) was found to be 0.68, its width (in heliographic latitude) 0.20 and its height 0.16 R _⊙ (Figure 5). The corresponding dimensions of the enclosed filament are 0.56 (length), 0.10 (width) and 0.08 (height) R _⊙.