High resolution solar flare X-ray spectra: The temporal behavior of electron density, temperature, and emission measure for two class M flares

Journal Article · Thu Oct 01 04:00:00 EDT 1981 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/159294· OSTI ID:5756614

Doschek, G A; Feldman, U; Landecker, P B; McKenzie, D L

High resolution soft X-ray flare spectra recorded by Naval Research Laboratory (NRL) and Aerospace Corporation Bragg crystal spectrometers flown on an orbiting spacecraft (P78-1) are combined and analyzed. THe instruments were launched on 1979 February 24 by the U.S. Air Force, and the data discussed in this paper cover the wavelength ranges, 1.82--1.97 A, 3.14--3.24 A, and 18.4--23.0 A. The NRL experiment (SOLFLEX) covers the two short wavelength ranges (highly ionized Fe and Ca lines) and the Aerospace experiment (SOLEX) covers the 18.4--23.0 A range, which includes the Ly..cap alpha.. O VIII line and the resonance, intercombination, and forbidden lines of O VII. We analyze the spectra of two flares which occurred on 1980 April 8 and May 9. Temporal coverage is fairly complete for both flares, including the rise and decay phases. Measurements of electron density N/sub e/ with rather high time resolution (about 1 minute) have been obtained throughout most of the lifetime of the two flares. These measurements were obtained from the O VII lines and pertain to flare plasma at temperatures near 2 x 10/sup 6/ K. Peak density seems to occur slightly before the times of peak X-ray flux in the resonance lines of Fe XXV, Ca XIX, and O VII, and for both flares the peak density is about 10/sup 12/ cm/sup -3/. Electron temperature T/sub e/ as a function of time is determined from the Fe and Ca spectra. Peak temperature for both flares is about 18 x 10/sup 6/ K. Differential emission measures and volume emission measures are determined from the resonance lines of O VII, Ca XIX, and Fe XXV. The number of electrons N/sub e/..delta..V and the volume ..delta..V over which the O VII lines are formed are determined from the O VII volume emission measure N/sub e//sup 2/..delta..V and the density N/sub e/. These quantities are determined as a function of time. The relationship of the low and high temperature regions is discussed.

• Research Organization: E. O. Hulburt Center for Space Research, Naval Research Laboratory
• OSTI ID: 5756614
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 249:1; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640104* -- Astrophysics & Cosmology-- Solar Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
CALCIUM IONS
CHARGED PARTICLES
ELECTROMAGNETIC RADIATION
ELECTRON DENSITY
EMISSION
IONIZING RADIATIONS
IONS
IRON IONS
LYMAN LINES
OXYGEN IONS
PLASMA
RADIATIONS
SOFT X RADIATION
SOLAR ACTIVITY
SOLAR FLARES
SPECTRA
X RADIATION
X-RAY SPECTRA