Doppler Redistribution of Resonance Polarization of the O VI 103.2 NM Line Observed Above a Polar Hole

Abstract

By using the rotation of the SOHO satellite of March 19, 1996, it was possible to obtain polarimetric observations of the O VI 103.2 nm line emitted in the solar corona at a height of about 270 arcsec above the limb. For that, we have taken advantage of the sensitivity of the SUMER spectrometer to the state of linear polarization of the radiation incoming on the wavelength scan mirror. SUMER may then be used as an analyser of linear polarization by interpreting the angular variation of the intensity of the studied line. The 0 VI 103.2 nm line is formed in the corona by a competition between local electronic excitation collisions and resonance scattering of the incident radiation of the same line incoming from the transition region. Thus the scattered line may be partially linearly polarized. Because the incident radiation is frequency dependent, and because the scattering ions are dragged along the solar wind velocity, the scattered line is shifted and dimmed by the Doppler effect and thus its intensity is sensitive to the solar wind velocity. In addition, it has been recently shown that the linear polarization parameters are also sensitive to the three components of the solar wind velocity field.

Here we will present the results of polarimetric observations and we will begin by an outline of the theory which will be put into operation for interpreting the observations.