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Astron. Astrophys. 351, 368-372 (1999)

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An unusually intense Ca II K line wing: possible role of particle acceleration in the lower atmosphere

M.D. Ding

Department of Astronomy, Nanjing University, Nanjing 210093, P.R. China (dmd@nju.edu.cn)

Received 16 November 1998 / Accepted 6 August 1999


The white-light flare on 1974 October 11 showed an unusual behavior: its Ca II K line reached at flare maximum an intensity of K1 as high as half of the continuum. This spectral feature cannot be explained by ordinary flare models. We present an abnormal model with an extremely hot temperature minimum region (TMR) that can reproduce the unusually high K1 intensity. However, this poses a very severe constraint on the energy requirement in the lower atmosphere. Since canonical heating models are insufficient to provide enough heating energy in lower layers, an in situ energy source may be required. We further investigate the possible role of a non-thermal particle beam injected from a lower layer. A beam of hecta-keV electrons (or MeV protons) can sufficiently heat the TMR and lead to the formation of a very hot TMR provided that the energy flux of the beam is large enough. Whether such kinds of particle beams exist needs to be checked by more theoretical and observational studies.

Key words: line: profiles – Sun: atmosphere – Sun: flares

Send offprint requests to: M.D. Ding

© European Southern Observatory (ESO) 1999

Online publication: November 2, 1999