Near-Infrared Circular Polarimetry and Correlation Diagrams in the Orion BN/KL Region: Contribution of Dichroic Extinction

TL;DR

This study uses near-infrared circular polarimetry to analyze the Orion BN/KL region, revealing the role of dichroic extinction and aligned grains in producing circular polarization around massive stars.

Contribution

It provides the first deep circular polarization image of Orion BN/KL in Ks band and establishes a relation linking dichroic extinction, polarization, and color excess.

Findings

Quadrupolar circular polarization structure around IRc2

Strong correlation between H-Ks color and circular polarization

Dichroic extinction significantly contributes to circular polarization

Abstract

We present a deep circular polarization image of the Orion BN/KL nebula in the Ks band and correlations of circular polarization, linear polarization, and H-Ks color representing extinction. The image of circular polarization clearly reveals the quadrupolar structure around the massive star IRc2, rather than BN. H-Ks color is well correlated with circular polarization. A simple relation between dichroic extinction, color excess, circular and linear polarization is derived. The observed correlation between the Stokes parameters and the color excess agrees with the derived relation, and suggests a major contribution of dichroic extinction to the production of circular polarization in this region, indicating the wide existence of aligned grains.