Polarization from Aligned Dust Grains in the $\beta$ Pic Debris Disk

Abstract

We present 870 $\mu$m ALMA polarization observations of thermal dust emission from the iconic, edge-on debris disk $\beta$ Pic. While the spatially resolved map does not exhibit detectable polarized dust emission, we detect polarization at the $\sim$3$\sigma$ level when averaging the emission across the entire disk. The corresponding polarization fraction is $P_{\text{frac}}$ = $0.51\pm 0.19$%. The polarization position angle $\chi$ is aligned with the minor axis of the disk, as expected from models of dust grains aligned via radiative alignment torques (RAT) with respect to a toroidal magnetic field ($B$-RAT) or with respect to the anisotropy in the radiation field ($k$-RAT). When averaging the polarized emission across the outer versus inner thirds of the disk, we find that the polarization arises primarily from the SW third. We perform synthetic observations assuming grain alignment via both $k$-RAT and $B$-RAT. Both models produce polarization fractions close to our observed value when the emission is averaged across the entire disk. When we average the models in the inner versus outer thirds of the disk, we find that $k$-RAT is the likely mechanism producing the polarized emission in $\beta$ Pic. A comparison of timescales relevant to grain alignment also yields the same conclusion. For dust grains with realistic aspect ratios (i.e., $s>1.1$), our models imply low grain-alignment efficiencies.

22 pages, 13 figures, 2 tables. Accepted for publication in the Astrophysical Journal. Materials accessible in the online version of the ApJ article include the FITS files used to make the ALMA images

References in corpus (28)

• Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 parsecs: The Southern Sample
• Radiative torques: Analytical Model and Basic Properties
• Tracing Magnetic Fields with Aligned Grains
• Molecular Gas Clumps from the Destruction of Icy Bodies in the $\beta$ Pictoris Debris Disk
• One Solution to the Mass Budget Problem for Planet Formation: Optically Thick Disks with Dust Scattering
• The Radial Distribution of Dust Particles in the HL Tau Disk from ALMA and VLA Observations
• The Carbon-Rich Gas in the Beta Pictoris Circumstellar Disk
• Spatially Resolved Magnetic Field Structure in the Disk of a T Tauri Star
• ALMA Reveals Transition of Polarization Pattern with Wavelength in HL Tau's Disk
• Exocometary gas structure, origin and physical properties around $\beta$ Pictoris through ALMA CO multi-transition observations
• Submillimeter polarization observation of the protoplanetary disk around HD 142527
• Subsonic Mechanical Alignment of Irregular Grains
• Kuiper Belt-Like Hot and Cold Populations of Planetesimal Inclinations in the $\beta$ Pictoris Belt Revealed by ALMA
• Grain Alignment and Polarized Emission from Magnetized T Tauri Disks
• The Inner Disk Structure, Disk-Planet Interactions, and Temporal Evolution in the Beta Pictoris System: A Two-Epoch HST/STIS Coronagraphic Study
• Stringent limits on the magnetic field strength in the disc of TW Hya: ALMA observations of CN polarisation
• The effect of dust composition and shape on radiation-pressure forces and blowout sizes of particles in debris disks
• An Ordered Magnetic Field in the Protoplanetary Disk of AB Aur Revealed by Mid-Infrared Polarimetry
• Intrinsic polarisation of elongated porous dust grains
• Solving grain size inconsistency between ALMA polarization and VLA continuum in the Ophiuchus IRS 48 protoplanetary disk
• Revisiting the pulsational characteristics of the exoplanet host star $\beta$ Pictoris
• The ALMA Development Roadmap
• Polarized emission by aligned grains in the Mie regime : application to protoplanetary disks observed by ALMA
• Low Level Carbon Monoxide Line Polarization in two Protoplanetary Disks: HD 142527 and IM Lup
• Characterizing the accuracy of ALMA linear-polarization mosaics
• The Explosion in Orion-KL as Seen by Mosaicking the Magnetic Field with ALMA
• 1.3mm polarized emission in the circumstellar disk of a massive protostar
• Mid-Infrared Polarization of Herbig Ae/Be Discs

Cited by in corpus (1)

• Multi-wavelength aperture polarimetry of debris disc host stars