Detalles de publicación
PP 06055
Anisotropic collisions and impact circular polarization. Application to the solar Halpha line
Instituto de Astrof\'isica de Canarias, E-38205 La Laguna,
Tenerife, Spain
Aims. In the light of recent contradictory observational results concerning the atomic polarization of solar \ion{H}{i} lines, our purpose is to present certain collisional effects that might contribute towards a possible explanation. In particular, we aim to draw attention
to the possibility of the creation of the "impact circular polarization". Methods. A general theoretical formulation of the problem of anisotropic collisions in the tensorial representation is obtained in an arbitrary symmetry of the relative velocity distribution. To try to understand in concrete terms and estimate the effect of these collisions in creating and increasing the atomic orientation, we determine an explicit expression of the alignment-to-orientation transfer rates between two hydrogen levels in the particular case of axial but non-cylindrical symmetry. Results. The anisotropic collisions could play a role in creating and increasing the atomic orientation by an alignment-to-orientation conversion mechanism (impact circular polarization). Physically, this is due to coherence transfer by anisotropic collisions. This transfer, and hence the creation of atomic circular polarization, can be achieved in different ways, which we describe in the case of the H$_\alpha$ line. However, for given solar conditions the alignment-to-orientation transfer rates seem to be 4 to 5 times smaller than the creation of the alignment rates responsible for the generation of the impact linear polarization.
to the possibility of the creation of the "impact circular polarization". Methods. A general theoretical formulation of the problem of anisotropic collisions in the tensorial representation is obtained in an arbitrary symmetry of the relative velocity distribution. To try to understand in concrete terms and estimate the effect of these collisions in creating and increasing the atomic orientation, we determine an explicit expression of the alignment-to-orientation transfer rates between two hydrogen levels in the particular case of axial but non-cylindrical symmetry. Results. The anisotropic collisions could play a role in creating and increasing the atomic orientation by an alignment-to-orientation conversion mechanism (impact circular polarization). Physically, this is due to coherence transfer by anisotropic collisions. This transfer, and hence the creation of atomic circular polarization, can be achieved in different ways, which we describe in the case of the H$_\alpha$ line. However, for given solar conditions the alignment-to-orientation transfer rates seem to be 4 to 5 times smaller than the creation of the alignment rates responsible for the generation of the impact linear polarization.