Observations of linear polarization in the H_alpha line during two solar flares

Details Observations of linear polarization in the H_alpha line during two solar flares Observations of linear polarization in the H_alpha line during two solar flares

Sep 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999a%26a...349..283v&link_type=abstract

Astronomy and Astrophysics, v.349, p.283-294 (1999)

Astronomy and Astrophysics

Astrophysics

23

Sun: Flares, Polarization, Instrumentation: Polarimeters

Scientific paper

Two chromospheric flares were observed in Meudon using an H_alpha flare polarimeter on 17() th July 1982 and 20() th June 1989. A careful reduction of the data sets has been done in order to remove the false polarization signals induced by atmospheric turbulence. In each event, linear polarization directed towards the disk center with a polarization degree of the order of 5% is detected. This polarization is correlated in time with the maximum of soft X-ray emission. One event also shows polarization parallel to the solar limb at the moment of maximum hard X-ray emission but with a poor signal to noise ratio. We interpret this polarization as impact polarization, resulting from the excitation of hydrogen atoms by anisotropic particles. The tangential polarization could be due to a beam of energetic electrons moving vertically. However, the best candidates to explain both tangential and radial polarization are beams of energetic protons with an energy below 100 keV entering into the chromosphere. The variation of the polarization direction could result from a modification of the magnetic topology during the flare.

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