Volume 412, Number 1, December II 2003
|Page(s)||271 - 280|
|Published online||25 November 2003|
Effect of anisotropic velocity distribution on the linear polarization of coronal lines
Does the ion cyclotron exist in the inner corona?
Max-Planck-Institut für Aeronomie, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany
Corresponding author: N.-E. Raouafi, firstname.lastname@example.org
Accepted: 3 September 2003
The effect of an anisotropic velocity field distribution of scattering ions on the polarization parameters of a spectral line emitted by resonance scattering is considered. The anisotropy of the velocity field distribution can be interpreted in terms of the ion-cyclotron effect that is believed to influence some heavy ions in the solar corona. We present a theoretical study of the Stokes parameters of a spectral line emitted by atoms or ions in the presence of a bi-Maxwellian velocity field distribution. It is found from test calculations that such a distribution measurably changes the polarization properties of the D2 coronal line. Consequently, measurements of the linear polarization of this line may serve as a new diagnostic of a possible bi-Maxwellian velocity distribution. As a preliminary application, the obtained theoretical results are used to interpret the polarization parameters of the D2 coronal line () measured using SUMER/SoHO observations. The obtained results are compatible with SUMER's observations for more reasonable solar wind parameters than for an isotropic velocity field distribution of the scattering ions. Thus, the outflow velocity field vector of the emitting ions is less inclined with respect to the polar axis of the Sun (the minimal value of the polar angle η is for an anisotropic velocity distribution versus for an isotropic velocity field distribution). These results are obtained assuming that the re-emitted photons come from a small area in the center of the coronal polar hole, with zero magnetic field. Since SUMER/SoHO observations integrate over the line of sight, the results of the current analysis must be considered preliminary pending computations including an integration along the line of sight.
Key words: polarization / scattering / line: profiles / Sun: corona / Sun: solar wind / Sun: UV radiation
© ESO, 2003
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.