Linear polarization of hydrogen Balmer lines in optically thick quiescent prominences. I - Theoretical Investigation
Résumé
The linear polarization of H-alpha and H-beta in quiescent prominences having a nonnegligible optical thickness in H-alpha is theoretically deduced, starting from a zero-order self-consistent model obtained by solving the conventional non-LTE problem in prominences. The results show that the fractional linear polarization in zero magnetic field decreases with increasing optical thickness of the prominence and is rotated a small angle with respect to the solar limb when the prominence is seen at a sharp angle with respect to its plane. They also show that the polarization diagrams have a less symmetrical shape with respect to the analogous diagrams obtained for the limiting case of negligible optical thickness.