On the emission from the white-light flare of 15 June 1991 in C I, C II, Mg II, and He II lines.
Abstract
Analyzes the spectra of the brightest kernel in the white-light flare of 15 June 1991 acquired during the impulsive phase. The emission lines of C I, C II, Mg II, and He II in the region λλ651.7 - 659.8 nm are investigated. The magnesium and carbon lines represent a range of flare plasma temperatures from about 8000 K (C I) to 20000 K (C II). The authors give the central peak intensity wavelength, the width at half maximum, and the total power radiated in the lines for the central part of the flare kernel. The C I, Mg II, and He II emissions are symmetrical, unshifted, they have a Gaussian profile. The C II λ657.8 nm profile is asymmetrical, it can be represented by two Gaussian profiles, one unshifted and the other redshifted, the latter corresponding to a dynamic plasma moving with a line-of-sight velocity of about 20 km/s. Nonthermal line broadening increases with flare plasma temperature from 4 km/s for T = 10000 K to 10 km/s for T = 20000 K. The observed He II λ656.0 nm line width gives T = 30000 K for the upper temperature limit in the He II emission region. The intensities of this line are also used to determine the upper level population and the upper limit of the lower level population in the corresponding transition (6-4). The population of level 4 was found to be by a factor of 100 higher than the population determined for other flares from the intensity of the He II λ468.4 nm (4-3) line under the assumption of its small optical thickness. The line He II λ468.6 nm seems not to be optically thin.
- Publication:
-
Kinematics and Physics of Celestial Bodies
- Pub Date:
- 1999
- Bibcode:
- 1999KPCB...15...36B
- Keywords:
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- Solar Flares: Carbon Lines;
- Solar Flares: Helium Lines;
- Solar Flares: Magnesium;
- Solar Flares: Line Profiles