X-Ray Line and Continuum Spectra of Solar Flares from 0.5 to 8.5 Angstroms

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Abstract
Two crystal spectrometers aboard the orbiting solar observatory OSO-4 cover the wavelength ranges 0.5 to 3.9 angstroms and 1.0 to 8.5 angstroms. Within this range, there appear emission lines from hydrogen-like and helium-like states of calcium, sulfur, silicon, magnesium, and aluminum. The Mg XII Lyman-α is present strongly in all x-ray flares. The most intense flares (such as class 3) produce strong Si XIV Lyman-α and often S XVI Lyman-α. Emission, in the form of Ka lines of highly ionized states of calcium, iron, aluminum, and silicon is usually present. The continuum from 1 to 10 angstroms always dominates the line emission by more than an order of magnitude. Electron temperatures derived from the slope of the continuum spectrum are in the range of 107 to 108 °K, considerably higher than theoretical ionization equilibrium temperatures.