Astronomy and Astrophysics – Astrophysics
Scientific paper
2005-02-14
Astronomy and Astrophysics
Astrophysics
to be published in A&A, 8 pages, 6 figures
Scientific paper
10.1051/0004-6361:20041654
High sensitivity observations of Halpha polarization of 30 flares of different sizes and disk positions are reported. Both filter and spectrographic techniques have been used. The ZIMPOL system eliminates spurious polarizations due to seeing and flat-field effects. We didn't find any clear linear polarization signature above our sensitivity level which was usually better than 0.1%. The observations include an X17.1 flare with gamma-ray lines reported by the RHESSI satellite. These results cast serious doubts on previous claims of linear polarization at the one percent level and more, attributed to impact polarization. The absence of linear polarization limits the anisotropy of energetic protons in the H$\alpha$ emitting region. The likely causes are isotropization by collisions with neutrals in the chromosphere and defocusing by the converging magnetic field.
Benz Arnold O.
Bianda Michele
Kueveler G.
Ramelli Renzo
Stenflo Jan Olof
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