Mid-Infrared Polarization of the Diffuse Interstellar Medium toward CygOB2-12

TL;DR

This study reports the first mid-infrared polarization detection toward CygOB2-12, revealing silicate grain alignment in the interstellar magnetic field through spectropolarimetry, providing insights into dust properties in the diffuse interstellar medium.

Contribution

First mid-IR polarization measurement toward CygOB2-12, showing silicate grain alignment and informing dust composition models in the diffuse interstellar medium.

Findings

Detected polarization of 1.24% near 10.2 micrometers

Polarization position angle measured at 126 degrees

Wavelength dependence consistent with silicate grain alignment

Abstract

We present the first mid-IR detection of the linear polarization toward the star CygOB2-12, a luminous blue hypergiant that, with Av of ~10 mag of foreground extinction, is a benchmark in the study of the properties of dust in the diffuse interstellar medium. The 8-13 micrometer spectropolarimetry, obtained with the CanariCam multi-mode camera at the Gran Telescopio Canarias (GTC), shows clear trends with wavelength characteristic of silicate grains aligned in the interstellar magnetic field. The maximum polarization, detected with 7.8 statistical significance near 10.2 micrometers, is (1.24 +/- 0.28) % with position angle (126 +/- 8) deg. We comment on these measurements in the context of recent models for the dust composition in the diffuse interstellar medium.