A Discussion on solar studies with special reference to space observations - Helium-like ion forbidden line emission, and solar active regions

A theory has been developed for interpreting the intensity of the 1s2 1S—1s2s 3S forbidden line in heliumlike ions in terms of electron density at the source. In a recent soft X -ray rocket experiment, this transition has been observed simultaneously from C v, N vi and O v ii. New values for the forbidden transition probabilities are derived in a semi-empirical m anner using this data. The new values lead to derived solar densities in active regions of between 1011 and 1013 cm-3.