Spectropolarimetric observations of the solar atmosphere in the Hα 6563 Å line

¹ Instituto de Astrofísica de Canarias, Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
e-mail: jjaumeb@iac.es
² Departamento de Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
³ Consejo Superior de Investigaciones Científicas, Madrid, Spain
⁴ Istituto Ricerche Solari (IRSOL), Università della Svizzera italiana (USI), 6605 Locarno-Monti, Switzerland
⁵ Astronomical Institute ASCR, v.v.i., Ondřejov, Czech Republic

Received: 20 July 2021
Accepted: 16 December 2021

Abstract

We present novel spectropolarimetric observations of the hydrogen Hα line taken with the Zürich Imaging Polarimeter (ZIMPOL) at the Gregory Coudé 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 is dominated 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) close to the limb quiet (plage) regions for the average longitudinal field strength over the spatio-temporal resolution element.