Linear polarization of the hydrogen H-alpha line in filaments. I - Theoretical investigation
Résumé
Results are presented of theoretical calculations of the expected linear polarization in H-alpha from a filament observed at different positions over the solar disk. The geometry of the filament is represented by an infinite cylinder with an elliptical cross section, standing horizontally over the solar surface. The calculation results indicate a clear effect of a magnetic field; it was found that the polarization degrees in the presence of a magnetic field can reach values of the order of 2 percent. In addition, there was an optical thickness effect on the polarization degree and direction. These results suggest that it is possible to use the observations of the H-alpha line from filaments to determine the magnetic field vector.