Non-Zeeman Circular Polarization of Molecular Maser Spectral Lines

TL;DR

This paper demonstrates that non-Zeeman circular polarization in molecular masers can be explained by anisotropic resonant scattering, revealing magnetic fields of a few times 15 mG in evolved star environments.

Contribution

It applies a resonant scattering model to explain non-Zeeman polarization signals in SiO masers, providing a physical mechanism and magnetic field estimates.

Findings

Antisymmetric and symmetric Stokes V profiles explained by scattering.

Magnetic field strengths of a few times 15 mG are sufficient.

Model matches observed polarization features in evolved stars.

Abstract

We apply the anisotropic resonant scattering model developed to explain the presence of non-Zeeman circular polarization signals recently detected in the $^{12}\mathrm{CO}\;\left(J=2\rightarrow1\right)$ and $\left(J=1\rightarrow0\right)$ transitions in molecular clouds to Stokes $V$ spectra of SiO $v=1$ and $v=2$, $\left(J=1\rightarrow0\right)$ masers commonly observed in evolved stars. It is found that the observed antisymmetric "S" and symmetric "$\cup$" or "$\cap$" shaped spectral profiles naturally arise when the maser radiation scatters off populations of foreground molecules located outside the velocity range covered by the background maser radiation. Using typical values for the relevant physical parameters, it is estimated that magnetic field strengths on the order of a few times 15 mG are sufficient to explain the observational results found in the literature.