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Astron. Astrophys. 322, 674-678 (1997)

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Lyman continuum as a diagnostic for nonthermal processes in solar flares

M.D. Ding 1, 2 and H. Schleicher 1

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

Received 9 September 1996 / Accepted 15 November 1996


We have computed the Lyman continuum intensities for different flare circumstances, namely, the temperature rise in the chromosphere, the downward shift of the transition region, and the nonthermal effect of a precipitating beam of electrons. All the three factors can enhance the intensity by various amounts. The third effect additionally lowers the color temperature of the Lyman continuum. It thus provides a diagnostic tool to discriminate whether there exists an obvious nonthermal effect of electron beam bombardment during solar flares. It is also suggested that the relative magnitudes of Lyman and Balmer continuum enhancements can be used to infer the energy distribution type of the beam electrons.

Key words: Sun: chromosphere – Sun: flares – Sun: UV radiation

Send offprint requests to: H. Schleicher

© European Southern Observatory (ESO) 1997

Online publication: June 5, 1998