EUV EMISSION-LINES OF O-IV OBSERVED IN SOLAR SPECTRA BY THE S-055 INSTRUMENT ON SKYLAB

Recent calculations of electron and proton impact excitation rates in O IV are used to derive the intensity ratios of lines in the similar t o 340-1350 Angstrom wavelength range as a function of electron tempera ture (T-e) and density (N-e). These results are presented in the form of ratio-ratio diagrams, which should in principle allow both N-e and T-e to be deduced for the O IV line emitting region of a plasma. Elect ron temperatures derived from ratio-ratio diagrams involving the 790 A ngstrom/554 Angstrom ratio, in conjunction with observational data for several solar features obtained with the Harvard S-055 spectrometer o n board Skylab, are found to be in reasonable agreement with the value of T-e expected from ionization equilibrium calculations. This provid es some support for the theoretical diagnostics presented in this pape r, and hence the atomic data used in their derivation. However other t emperature and density sensitive ratios involving the O IV multiplets at 609 Angstrom, 625 Angstrom and 787 Angstrom could not be used to de rive plasma parameters from the ratio-ratio diagrams, due to blending with lines of Mg X and S V.