Spectropolarimetric observations of the solar atmosphere in the H$\alpha$ 6563 \r{A} line

TL;DR

This paper reports new spectropolarimetric observations of the solar Hα line, revealing complex polarization patterns influenced by scattering, Hanle, and Zeeman effects, which can help probe the solar chromosphere's magnetic and scattering properties.

Contribution

It provides the first detailed spectropolarimetric analysis of the Hα line with spatial variability insights, including polarization patterns in coronal holes and near the limb.

Findings

Linear polarization dominated by scattering and Hanle effect.

Different polarization behaviors observed near solar poles.

Estimated magnetic field strengths of 10 G in quiet regions and 40-60 G in plage areas.

Abstract

We present novel spectropolarimetric observations of the hydrogen H$\alpha$ line taken with the Z\"urich Imaging Polarimeter (ZIMPOL) at the Gregory Coud\'e Telescope of the Istituto Ricerche Solari Locarno (IRSOL). The linear polarization is clearly dominated by the scattering of anisotropic radiation and the Hanle effect, while the circular polarization by the Zeeman effect. The observed linear polarization signals show a rich spatial variability, the interpretation of which would open a new window for probing the solar chromosphere. We study their spatial variation within coronal holes, finding a different behaviour for the $U/I$ signals near the North and South solar poles. We identify some spatial patterns, which may facilitate the interpretation of the observations. In close-to-the-limb regions with sizable circular polarization signals we find similar asymmetric $Q/I$ profiles. We also show examples of net circular polarization profiles (NCP), along with the corresponding linear polarization signals. The application of the weak field approximation to the observed circular polarization signals gives $10\,$G ($40-60\,$G) in close to the limb quiet (plage) regions for the average longitudinal field strength over the spatio-temporal resolution element.