Fe XXVI line emission observed by YOHKOH
Abstract
Observations from the Bragg Crystal Spectrometer (BCS) on board the Japanese solar flare space-craftYohkoh showing Fe xxvi Ly-alpha X-ray line emission at about 1.78 Angstroms are reported. Some 75 events over a two-year-long period between December 1991 and December 1993 have been analyzed. The greater sensitivity of the BCS compared with previous instruments has enabled such emission to be detected from a wider group of flares than has previously been possible. The likelihood of detecting Fe xxvi lines in a flare is found to increase sharply with the electron temperature obtained from the Fe xxv line spectrum, also observed by the BCS, and with GOES X-ray class. The width of the Lyalpha_1 line, measured after the impulsive stage, is rather greater than that determined by thermal Doppler broadening, and if the excess broadening is attributed to turbulence, velocities of up to 70 km s^-1 are indicated. Comparison of electron temperatures obtained from the Fe xxvi spectrum with Fe xxv temperatures provides evidence for a single loose grouping of flares, with the difference between the two temperatures ranging from nearly zero to about 20 x 10^6K. A ``superhot'' component would seem to be more or less developed according as the temperature difference is large or nearly zero.
- Publication:
-
Advances in Space Research
- Pub Date:
- March 1996
- DOI:
- 10.1016/0273-1177(95)00540-U
- Bibcode:
- 1996AdSpR..17d..51P
- Keywords:
-
- Emission Spectra;
- Iron Isotopes;
- Line Spectra;
- Lyman Alpha Radiation;
- Solar Flares;
- X Ray Astronomy;
- X Ray Spectra;
- Doppler Effect;
- Electron Energy;
- Japanese Spacecraft;
- Proportional Counters;
- Satellite-Borne Instruments;
- Spectral Resolution;
- Solar Physics