Evolutional Characteristics of Multiple Spectral Lines during the Impulsive Phase of Solar Flares

Astronomy and Astrophysics – Astronomy

Scientific paper

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Line Profiles, Sun: Chromosphere, Sun: Flares, Sun: Spectra

Scientific paper

A study of the impulsive phase spectra of two chromospheric flares, for which the Hα , CaII K, HeI D_3, NaI D_{1,2} and other metallic lines were simultaneously obtained with high temporal and spatial resolutions, is presented. The main new observational results are: (1) The red-shifted emission streaks observed in the Hα , K, and D_3\ lines give nearly the same downward velocities, the maximum of which ranges from 50 to 100 km s(-1) for typical streaks. (2) The broad Hα , K, and D_3\ line profiles are well explained by a Doppler broadening of nearly the same turbulent velocity, the maximum of which ranges between 120 and 170 km s(-1) . (3) D_{1,2}\ and metallic line emissions show narrow and slightly red-shifted profiles. Their typical maximum downward and turbulent velocities are 2--6 km s(-1) \ and 10 km s(-1) , respectively. (4) K-line emission profiles of the flares consist of two components, i.e., a red-shifted broad wing and a stationary narrow core. (5) All of the emission lines show nearly parallel time-profiles of both the intensity and downward velocity. From these results we conclude that the emitting region of the chromospheric flare consists of two layers heated simultaneously: one relatively thin, fast-downward-moving and very turbulent, and the other almost stationary and optically thick in metallic-line emissions.

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