Application to astrophysics of collisional polarization spectroscopy

Collisional polarization specroscopy brings unique information on the aniso tropies of the velocity distribution function of energetic particles, allow ing the identification of these particles and the evaluation of the energy flux they carry. The application of collisional polarization spectroscopy i s still limited to Solar Physics. Chromospheric hydrogen Palmer lines H alp ha and H beta have been found to be linearly polarized in solar flares. The polarization seems to be associated with enhanced soft X-ray emission and is found to be in the flare to disk center direction. In the hypothesis whe re particles are accelerated higher in the solar corona, protons of energy lower than 1 MeV are found to be the best candidates to explain the observe d polarization. The significant degree of polarization of a few per cent ob served may also indicate a low local acceleration site but still requires t he acceleration of protons in the 10 to 100 keV energy range.