MG-IX LINE RATIOS IN THE SUN

Theoretical Mg IX electron density sensitive emission-line ratios, derived using electron impact excitation rates interpolated from accurate R-matrix calculations, are presented for R1 = I(443.97 angstrom)/(368.07 angstrom), R2 = I(439.17 angstrom)/I(368.07 angstrom), R3 = I(368.07 angstrom)/I(443.07 angstrom), and R4 = I(441.20 angstrom)/I(368.07 angstrom). A comparison of these with observational data for solar flares, obtained with the Naval Research Laboratory's S082A spectrograph on board Skylab, reveals excellent agreement between theory and observation for R1 and R2, which confirms the usefulness of these ratios as N(e)-diagnostics for solar flares, as well as providing experimental support for the accuracy of the atomic data adopted in the line ratio calculations. However the observed values of both R3 and R4 generally imply unrealistically high electron densities, which is probably due to blending in the 443.40 and 441.20 angstrom lines, probably with Ar IV 443.44 angstrom and Mg VI/Mg VII 441.22 angstrom, respectively.