X-ray emission-line ratios in MG XI as electron temperature diagnostics for solar flares and active regions

Abstract

Electron impact excitation rates for transitions in helium-like Mg XI, calculated with the R-matrix code, are used to derive the electron temperature-sensitive emission-line ratios G = [I(1s2 1S-1s2s 3S) + I(1s2 1S-1s2p 3P1,2)]/I(1s2 1S-1s2p 1P) = [I(9.314 angstrom) + I(9.232 angstrom)]/I(9.169 angstrom), R1 = I(1s2 1S-1s3p 1P)/I(1s2 1S-1s2p 1P) = I(7.850 angstrom)/I(9.169 angstrom), and R2 = I(1s2 1S-1s4p 1P)/I(1s2 1S-1s2p 1P) = I(7.472 angstrom)/I(9.169 angstrom). These are found to be significantly different from the earlier diagnostic calculations of Keenan, Tayal, & Kingston, and Keenan, Kingston, & McKenzie, and will lead to electron temperature estimates up to a factor of approximately 1.6 larger. Values of T(e) deduced from R1 and R2 ratios measured from solar flare and active region spectra obtained with the Flat Crystal Spectrometer (FCS) on board the Solar Maximum Mission (SMM) satellite are consistent, and furthermore are in good agreement with temperatures estimated from the observed G ratios for these solar features. This provides support both for the validity of the theoretical R1 and R2 diagnostics, and for the FCS calibration curve in the wavelength region covering the Mg XI transitions, 7.472-9.314 angstrom.