Possible creation of net circular polarization and not only depolarization of spectral lines by isotropic collisions

TL;DR

This paper proposes a new mechanism where isotropic collisions can generate net circular polarization in spectral lines, potentially explaining previously unexplained solar observations, with initial results shown for the Hα line.

Contribution

It introduces a novel collisional mechanism that creates net orientation of atomic levels, leading to symmetric Stokes-V profiles, contrasting with traditional Zeeman effect expectations.

Findings

Isotropic collisions can produce symmetric Stokes-V profiles.

The amplitude of symmetric lobes can surpass antisymmetric components.

Preliminary results demonstrate this effect for the Hα spectral line.

Abstract

We will show that isotropic collisions of electrons and protons with neutral hydrogen can lead to creation of net orientation of the atomic levels in the presence of a magnetic field. Consequently, the emitted Stokes-V profile of the spectral lines can be almost symmetric in contrast to the typical antisymmetric signature of the Zeeman effect. Moreover, the amplitude of the symmetric lobe can be significantly higher than the amplitude of the antisymmetric components. This mechanism is caused by a $\pm{M}$ symmetry breaking of the collisional transitions between different Zeeman sublevels. We will show an example of our first results for the H$\alpha$ line. This new mechanism could perhaps explain the net circular polarization of spectral lines observed in some solar limb observations and which are currently not understood. However, our results are very preliminary and more developments are needed for going further on.