Spectropolarimetric observations of the solar atmosphere in the H$\alpha$ 6563 Å line

Abstract

We present novel spectropolarimetric observations of the hydrogen H$\alpha$ 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 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.

Accepted in A&A (16/12/2021)

References in corpus (6)

• Recovering Thermodynamics from Spectral Profiles observed by IRIS: A Machine and Deep Learning Approach
• The effects of three-dimensional radiative transfer on the resonance polarization of the Ca I 4227 $\mathring{\mathrm{A}}$ line
• Automating Ellerman bomb detection in ultraviolet continua
• Scattering Polarization of Hydrogen Lines in Weakly Magnetized Stellar Atmospheres I. Formulation and Application to Isothermal Models
• Classification of High-resolution Solar Hα Spectra using t-distributed Stochastic Neighbor Embedding
• Spatio-temporal evolution of Hanle and Zeeman synthetic polarization in a chromospheric spectral line

Cited by in corpus (3)

• Optimal spectral lines for measuring chromospheric magnetic fields
• Does H$\alpha$ Stokes~$V$ profiles probe the chromospheric magnetic field? An observational perspective
• Simultaneous spectropolarimetric observations in the H$\alpha$ and Ca II 8662 Å lines of an active region