A New Mechanism for Polarizing Light from Obscured Stars

TL;DR

This paper introduces a novel optical pumping mechanism to explain the observed polarization variability in obscured Herbig AeBe stars, suggesting a new interpretation of polarization signals in stellar environments.

Contribution

The study proposes a new model based on optical pumping to explain polarization variability, differing from traditional scattering-based explanations.

Findings

Optical pumping can produce larger polarization signals than scattering.

Polarization variability correlates with absorptive parts of line profiles.

The model explains wavelength and epoch-dependent polarization changes.

Abstract

Recent spectropolarimetric observations of Herbig AeBe stellar systems show linear polarization variability with wavelength and epoch near their obscured H-alpha emission. Surprisingly, this polarization is not coincident with the H-alpha emission peak but is variable near the absorptive part of the line profile. With a new and novel model we show here that this is evidence of optical pumping - anisotropy of the incident radiation that leads to a linear polarization-dependent optical depth within the intervening hydrogen wind or disk cloud. This effect can yield a larger polarization signal than scattering polarization in these systems.