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Astron. Astrophys. 318, L17-L20 (1997)


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Letter to the Editor

Influence of non-thermal processes on line asymmetries in solar flares

M.D. Ding 1, 2 and C. Fang 2

1 Kiepenheuer-Institut für Sonnenphysik, Schöneckstr. 6, D-79104 Freiburg, Germany
2 Department of Astronomy, Nanjing University, Nanjing 210093, China

Received 3 September 1996 / Accepted 28 November 1996

Abstract

We make line profile calculations for a flare atmosphere considering simultaneously the effect of non-thermal excitation and ionization of the hydrogen atoms caused by precipitating high-energy electrons, and the effect of possible chromospheric downflows. The results confirm the earlier finding that a downflow, if confined to the upper chromosphere, can sometimes produce a blue asymmetry of the H [FORMULA] line. In addition, we find that the existence of such non-thermal effects tends to enhance the blue-asymmetry magnitude. In particular, the larger the energy flux, or the harder the energy spectrum for the beam electrons, the easier it will be to produce a blue-asymmetric H [FORMULA] profile, which is simultaneously intensified and broadened. Possible reasons which make the blue asymmetry less popular than the red asymmetry in observations are discussed.

Key words: Line: profiles – Sun: flares

Send offprint requests to: M.D. Ding (Nanjing University)

© European Southern Observatory (ESO) 1997

Online publication: July 8, 1998

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