NIV line ratios in the Sun

Theoretical Niv emission line ratios, which incorporate several improvements over previous estimates, are presented for R ₁ = I(923.2 Å)/I(765.1 Å) and R ₂ = I(1718.6 Å)/I(1486.5 Å), which are electron density and temperature sensitive, respectively. A comparison of R ₁ with observational data for several solar features obtained with the Harvard S-055 spectrometer on board Skylab reveals generally good agreement between theory and observation, except for the quiet Sun, which is probably due to the 923.2 Å line being blended with an Feiii transition in this instance. The observed value of R ₂, determined from a quiet-Sun spectrum obtained by the S082-B spectrograph on board Skylab, implies an electron temperature in excellent agreement with that of maximum Niv fractional abundance in ionisation equilibrium, which provides observational support for the accuracy of the diagnostic calculations.