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Astron. Astrophys. 341, 896-901 (1999)


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Velocity distribution function anisotropy of soft X-ray generated photoelectrons and resulting H[FORMULA] polarization in solar flares

J.-C. Hénoux 1 and M. Karlický 2

1 Observatoire de Paris, DASOP-URA2080 (CNRS), F-92195 Meudon Cedex, France
2 Astronomical Institute of the Academy of Sciences of Czech Republic, CZ-25165 Ondejov, Czech Republic

Received 14 August 1998 / Accepted 27 October 1998

Abstract

Soft X-rays irradiation of the solar atmosphere during solar flares generates photoelectrons which have an anisotropic velocity distribution. Using a 1-D test particle code, the anisotropy of the photoelectrons velocity distribution is derived, and the maximum degree of linear polarization in the hydrogen H[FORMULA] and H[FORMULA] lines that photoelectrons could generate by impact is estimated. Over a band pass of 0.75 and 0.5 Å, the net polarization degree expected in both lines is predicted not to exceed 0.2%. Therefore, soft X-ray irradiation cannot explain the one order of magnitude higher degree of linear polarization observed in solar flares.

Key words: line: formation – polarization – Sun: flares – Sun: particle emission – Sun: X-rays, gamma rays

Send offprint requests to: J.C. Hénoux

Correspondence to: J.C. Hénoux

© European Southern Observatory (ESO) 1999

Online publication: December 16, 1998

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