Dielectronic satellite spectra for highly charged helium-like ions - IV. Iron satellite lines as a measure of non-thermal electron energy distributions

The intensities of two satellite lines $$1\,{S}^{2}\,nl\,-\,1s\,2pnl\,\text{with}\,n\,=\,2$$ and 3 relative to the Fe xxv resonance line $$1\,{s}^{2}\,-\,1s\,2p$$ are considered. The intensities of these three lines are described by a single temperature only if the emitting plasma has a Maxwellian distribution of electrons. Analysis of the measured relative line intensities is proposed as a means of detecting departures from Maxwellian distributions, such as occur in solar flares. No data yet exist with the required quality to which the method may be applied, but an illustration is provided by two flares in which non-thermal electrons are present, and expected line ratios are deduced from these.