Mid-Infrared Polarization of Herbig Ae/Be Discs

TL;DR

This study used mid-infrared polarization measurements to investigate magnetic fields in protoplanetary discs around Herbig Ae/Be stars, revealing diverse magnetic field configurations and a high detection rate of polarization.

Contribution

First mid-infrared polarization survey of Herbig Ae/Be discs providing insights into magnetic field structures and grain alignment in these environments.

Findings

Detected polarization in 8 out of 9 objects, indicating common magnetic fields.

No preferred magnetic field configuration; various structures inferred.

Polarization likely due to emission/absorption, with some scattering contributions.

Abstract

We measured mid-infrared polarization of protoplanetary discs to gain new insight into their magnetic fields. Using CanariCam at the 10.4 m Gran Telescopio Canarias, we detected linear polarization at 8.7, 10.3, and 12.5 $\mu$m from discs around eight Herbig Ae/Be stars and one T-Tauri star. We analyzed polarimetric properties of each object to find out the most likely interpretation of the data. While the observed mid-infrared polarization from most objects is consistent with polarized emission and/or absorption arising from aligned dust particles, we cannot rule out polarization due to dust scattering for a few objects in our sample. For those objects for which polarization can be explained by polarized emission and/or absorption, we examined how the derived magnetic field structure correlates with the disc position angle and inclination. We found no preference for a certain type of magnetic field. Instead, various configurations (toroidal, poloidal, or complex) are inferred from the observations. The detection rate (64 per cent) of polarized mid-infrared emission and/or absorption supports the expectation that magnetic fields and suitable conditions for grain alignment are common in protoplanetary discs around Herbig Ae/Be stars.