Line polarization observed in chromospheric flares - Calculations for electron impact excitation of H-alpha

Details Line polarization observed in chromospheric flares - Calculations for electron impact excitation of H-alpha Line polarization observed in chromospheric flares - Calculations for electron impact excitation of H-alpha

Aug 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992a%26a...262..302a&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 262, no. 1, p. 302-307.

Astronomy and Astrophysics

Astrophysics

12

Chromosphere, Electron Impact, H Alpha Line, Linear Polarization, Solar Electrons, Solar Flares, Astronomical Polarimetry, Solar Atmosphere, Solar Corona

Scientific paper

The observation of chromospheric flares accompanying coronal flares in the sun indicates fast energy transfer between the two layers. Polarization observed in the H-alpha and S I lines can help to explain the nature of this energy transfer if accurate atomic data for the line polarization is available. Calculations for H-alpha line polarization by low-energy electron impact are presented, using the most sophisticated collision data available to date. The theoretical results compare well with polarization measurements dating from 1968. Low-energy electrons with anisotropic velocity distributions could be present in solar flares. They could be associated either with proton bombardment or with the existence of large temperature gradients. Assuming that the polarization of H-alpha observed in chromospheric flares is due only to electron impact, the ratio of the two even moments J2 and J0 of the electron velocity distribution is inferred. Further, under the hypothesis that the anisotropy is due to a high temperature gradient, a velocity distribution function for electrons carrying a conductive heat flux is linked to the observed polarization.

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