He II emission from solar flares

The first monochromatic images of a solar flare in the 4686-angstrom line of He II are presented. The observations were obtained in the intense (X10) flare 1984 May 20. The emission comes from footprint kernels with peak intensity 3.3 times the photosphere, or 0.9 times after subtraction of photospheric background and continuum. This value is about twice that recorded by spectroscopic observers and far exceeds most published data for the intensity of the resonance line at 304 angstroms and the Balmer alpha line of He II at 1640 angstroms. The intensities of the He II lines were calculated for a range of temperature and electron density, using a six-level atom with enhanced XUV incoming flux.