Diagnostic application of highly ionized iron lines in the XUV spectrum of a solar flare

Recent atomic data have been used to analyze a solar flare spectrum obtained with the Goddard Space Flight Center's grating spectrometer on the OSO-5 satellite. There exist in the wavelength region 90-200 A strong lines from each of the ions FeXVIII-FeXXIV. The FeXXI lines can be used as an electron density diagnostic for the 107 K plasma. From our analysis of a particular flare, we find a steep positive slope in the emission measure between 10sup(6.5) and 10sup(7.2) K and an electron density of approx.= 4 x 1011 cm-3 at 107 K. We emphasise the need for high spectral and spatial resolution observations of solar flares in this wavelength region, which has to date been largely neglected. (orig.)