The 1 1S--n 1P/1 1S--2 1P Emission-Line Ratios in SI XIII as Electron Temperature Diagnostics for Solar Flares and Active Regions
Theoretical Si XIII emission-line ratios R1, R2, and R3 are presented as a function of electron temperature. These ratios are found to be more electron temperature sensitive than the commonly used diagnostic for He-like ions (G), with, for example, R1, R2, and R3 varying by factors of approximately 6, 12, and 17 between log Te = 6.2 and 7.2, while G only changes by a factor of 1.8. In addition, R1, R2, and R3 are less dependent on whether or not the Si XIII-emitting plasma is in ionization equilibrium. Electron temperatures deduced using the observed values of R1, R2, and R3 from OV 1-17 and OSO 8 satellite spectra of solar flares and active regions are in good agreement and, in general, compared favorably with those determined from G. However, in the case of measurements made with the Flat Crystal Spectrometer on board the Solar Maximum Mission satellite there are large discrepancies between theory and observation. Possible explanations for these are briefly discussed.