Interpretation of Solar Helium-Like Ion Line Intensities

Recent identification of the $${2}^{3}\,S\rightarrow {1}^{1}\,S$$ line from helium-like ions in the solar soft X-ray spectrum, followed by calculation of its transition probability, enables an analysis of the observations to be carried out, based on intensities of the three lines $${2}^{1}\,\text{P}\rightarrow {1}^{1}\,S,\,{2}^{3}P\rightarrow {1}^{1}S,\text{and}\,{2}^{3}\,S\rightarrow {1}^{1}S$$. The relative collision rates to the excited levels and the electron densities in the emitting regions have been determined, subject to the limitation of available observations. Densities of $$\simeq 3\,\times {10}^{8}\,\text{cm}^{-3}$$ are found from lines formed over the quiet corona, but values of between 10⁹ and 10¹¹ cm^–3 are found from lines emitted in active regions, and the highest electron densities occur in the hottest regions.