Polarized Forbidden Coronal Line Emission in the Presence of Active Regions

• Published in: Solar physics Vol. 296; no. 11
• Main Authors: Schad, Thomas, Dima, Gabriel
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01.11.2021; Springer Nature B.V
• Subjects: Anisotropy; Astrophysics and Astroparticles; Atmospheric Sciences; Broken symmetry; Continuum radiation; Corona; Coronal ions; Coronal magnetic fields; Emission analysis; Emissions; Induced polarization; Magnetic fields; Photosphere; Physics; Physics and Astronomy; Plasmas (physics); Polarization; Radiation; Solar magnetic field; Solar physics; Space Exploration and Astronautics; Space Sciences (including Extraterrestrial Physics; Sunspots; Symmetry; Wavelengths; Zeeman effect; Polarization, optical; Magnetic fields, corona
• ISSN: 0038-0938; 1573-093X
• DOI: 10.1007/s11207-021-01917-y

Photoexcited forbidden lines at visible and infrared wavelengths provide important diagnostics for the coronal magnetic field via scattering induced polarization and the Zeeman effect. In forward models, the polarized formation of these lines is often treated assuming a simplified exciting radiation field consisting only of the photospheric quiet-Sun continuum, which is both cylindrically-symmetric relative to the solar vertical and unpolarized. In particular, this assumption breaks down near active regions, especially due to the presence of sunspots and other surface features that modify the strength and anisotropy of the continuum radiation field. Here we investigate the role of symmetry-breaking on the emergent polarized emission in high resolution models of the active corona simulated with the MURaM code. We treat the full 3D unpolarized continuum radiation field of the photosphere that excites the coronal ions and compare the cases where the symmetry-breaking effects of the photospheric features are included or ignored. Our discussion focuses on the key observables soon to be available by the National Science Foundation’s Daniel K Inouye Solar Telescope . The results indicate that while symmetry breaking can in principle have a large effect, its role is relatively minor for the simulated active region, largely due to the low inherent polarization fraction emitted by forbidden lines in denser active region plasmas.