Scattering polarization in strong chromospheric lines

II. Influence of the temperature curve on the Ca II K line

¹ Institute of Astronomy, ETH Zentrum, 8092 Zurich, Switzerland e-mail: [holzreuter;stenflo]@astro.phys.ethz.ch
² Faculty of Mathematics & Science, University of Zurich, 8057 Zurich, Switzerland

Received: 14 November 2006
Accepted: 23 January 2007

Abstract

In a previous paper we analyzed the polarization profile of the K line near the limb at . We now extend this work to model the center-to-limb variation of the linear polarization of the K line and compare it with calculated spectra based on standard 1D model atmospheres. Our previous two-component approach with a hot and a cool atmospheric component is re-examined. We confirm our previous result that no single model is able to explain the observations. While self-consistent single atmosphere solutions may fit the polarization spectra, they fail to simultaneously fit the corresponding intensity spectra or the polarization spectra at other heliocentric angles. The mixing of a cool and a hot component is however a good approach for all disk positions, although the optimum mixing ratio varies strongly with heliocentric angle. As we approach the limb the hot component gains in importance, which is consistent with the scenario of diverging magnetic canopies overlying a cool atmosphere.