Observationally derived magnetic field strength and 3D components in the HD 142527 disk

TL;DR

This study uses multi-wavelength polarization observations of the HD 142527 disk to derive the 3D magnetic field components and strength, providing key parameters for understanding magnetic activity in protoplanetary disks.

Contribution

It introduces a novel method to measure the 3D magnetic field components in protoplanetary disks using polarization angle offsets, with application to HD 142527.

Findings

Magnetic field components estimated as |B_r|:|B_φ|:|B_z| ≈ 0.26:1:0.23.

Magnetic field strength around 200 au is approximately 0.3 milli-Gauss.

Radial and vertical angular momentum transfer are comparable.

Abstract

In protoplanetary disks around young stars, magnetic fields play an important role for disk evolution and planet formation. Polarized thermal emission from magnetically aligned grains is one of the reliable methods to trace magnetic fields. However, it has been difficult to observe magnetic fields from dust polarization in protoplanetary disks because other polarization mechanisms involving grown dust grains become efficient. Here, we report multi-wavelength (0.87 mm, 1.3 mm, 2.1 mm, and 2.7 mm) observations of polarized thermal emission in the protoplanetary disk around HD 142527, showing the lopsided dust distribution. We revealed that the smaller dust still exhibits magnetic alignment in the southern part of the disk. Furthermore, angular offsets between the observed magnetic field and the disk azimuthal direction were discovered, which can be used as a method to measure the relative strengths of each component (radial ($B_r$), azimuthal ($B_\phi$), and vertical ($B_z$)) of 3D magnetic field. Applying this method, we derived the magnetic field around a 200-au radius from the protostar as $|B_r |:|B_\phi |:|B_z | \sim 0.26:1:0.23$ and a strength of $\sim 0.3$ milli-Gauss. Our observations provide some key parameters of magnetic activities including the plasma beta, which have only been assumed in theoretical studies. In addition, the radial and vertical angular momentum transfer are found to be comparable, which poses a challenge to theoretical studies of protoplanetary disks.