Showing papers by "James R. Lemen published in 1979"

An investigation of the 1.9 Å feature in solar-flare X-ray spectra.

Abstract: The 1.9 A feature, observed in the X-ray spectra of three solar flares with the Columbia University and Lockheed Palo Alto Research Laboratory spectrometers on the OSO 8 satellite, is shown to be due to a blend of 1s-2p transitions in a range of Fe ions. In the temperature range 9-16 x -10 to the 6th K, the feature has a mean wavelength of 1.900 + or - 0.009 A and is 0.04 A wider than a single line, indicating that the main contributors are Fe XIX-Fe XXII. Most of the emission originates from the dielectronic recombination process, and when inner-shell excitation is included together with normal collisional excitation, the observed intensity of the feature can be accounted for adequately. For these events, if the electron density is below approximately 10 to the 12th/cu cm, deviations from ionization equilibrium will be significant for ions more highly ionized than Fe XXI.