Emissions ‘froides’ dans la couronne solaire

Prominences have been photographed through a coronagraph and an H Lyot filter with long exposure times. Faint H emissions are often detected down to the threshold 2 × 10^-6 times of the Sun's brightness; they show definite structures but their relations to the low-level ordinary prominences are not very clear. Estimates are given for the density and thickness of such cool regions.