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Title:
The allowed lines of O IV near 1340 A in high electron density solar flares
Authors:
Cook, J. W.; Keenan, F. P.; Bhatia, A. K.
Affiliation:
AA(Naval Research Lab., Washington, DC, US), AB(Naval Research Lab., Washington, DC, US), AC(NASA. Goddard Space Flight Center, Greenbelt, MD, US)
Publication:
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 425, no. 2, p. 861-864 (ApJ Homepage)
Publication Date:
04/1994
Category:
Solar Physics
Origin:
STI
NASA/STI Keywords:
ELECTRON DENSITY (CONCENTRATION), LINE SPECTRA, OXYGEN, SOLAR FLARES, ELECTRON ENERGY, ELECTRON TRANSITIONS, PLASMA DENSITY, SKYLAB PROGRAM, SPECTROGRAPHS
DOI:
10.1086/174032
Bibliographic Code:
1994ApJ...425..861C

Abstract

Intersystem lines of O IV near 1400 A have long been used as electron density diagnostics for solar plasmas at temperatures of around 160,000 K. In addition, however, several allowed lines of O IV near 1340 A should become visible in conditions of high plasma electron number density (greater than 1012/cu cm), such as during a solar flare. We present observations of the 1340 A and 1400 A regions of the solar spectrum for two solar flares, obtained by the SO82B spectrograph on board Skylab. We examine three candidate lines for allowed O IV in the flare spectra which occur at the correct wavelengths, but show that two of these are actually blends dominated by resonantly excited molecular lines of H2. The third candidate line, at 1343.51 A, we identify as the O IV allowd line. We present the density and temperature sensitivity of the ratio of allowed and intersystem O IV lines R = I(1343.51 A)/I(1407.39 A). The 1343.51 A line is clearly present in the first solar flare spectrum, and the ratio value implies an electron density of log Ne = 12.6. The second flare has a much weaker 1343.51 A profile, but again the ratio value implies a high electron density. Both these electron density values are in good agreement with estimates for each flare from independent diagnostic ratios. The simple presence alone of a clearly observed O IV 1343.51 A emission line implies an electron density greater than 1012/cu cm.

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