The He-D3 to H-beta emission ratio in prominences

Solar prominences have been observed simultaneously in the integrated emission of the He-D3 and the H-beta lines on two successive days at the SST on La Palma. The line intensities and their ratio show spatial and temporal variations of mainly two types: (a) constant emission ratio with substantial intensity variations, (b) varying ratio related with intensity changes. Both findings may be explained by a different arrangement of prominence structures (threads) along the line-of-sight with (a) different numbers or (b) different 'packing density' of threads.