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Astron. Astrophys. 338, 737-746 (1998)

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Generation of solar H[FORMULA] impact polarization by fragmented evaporative upflows

L. Fletcher and J.C. Brown

Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QT, UK

Received 13 December 1995 / Accepted 3 June 1998


In this paper a novel mechanism is proposed for the generation of H[FORMULA] impact polarization observed during some solar flares. Rather than being generated by the primary particle beams transporting energy from the chromosphere to the corona, we suggest that following heating, the solar chromosphere evaporates in a fragmented manner, and that impact excitations in the regions of interaction of hot evaporating and cool non-evaporating material locally generates impact-polarized H[FORMULA] emission. This thermal upflow model is more consistent with the large areas and times over which polarization is observed than are beam models. A simple model for the process is given, and the resulting polarization is calculated and compared with observations, under two assumptions about the number density of neutral particles in the interaction regions.

Key words: Sun: flares – Sun: chromosphere – polarization

Send offprint requests to: L. Fletcher: from 1 May 1998 at Lockheed-Martin Solar and Astrophysics Laboratory, Dept. H1-12, Building 252, 3251 Hanover St., Palo Alto, CA 94304, USA (fletcher@sag.lmsal.com)

© European Southern Observatory (ESO) 1998

Online publication: September 14, 1998