Using ALMA to understand the origin of dust polarization in the Beta Pic debris disk

2022 Fiscal Year Final Research Report

• Project/Area Number: 20K14527
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 16010:Astronomy-related
• Research Institution: National Astronomical Observatory of Japan
• Principal Investigator: HULL CHARLES 国立天文台, アルマプロジェクト, 特別客員研究員 (70814755)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: Star formation / Radio astronomy / Polarization / Dust / Debris disks / Magnetic fields / Scattering

Outline of Final Research Achievements

Our ALMA polarization observations of thermal dust emission from the iconic, edge-on debris disk β Pic were published in 2022. While the spatially resolved map does not exhibit detectable polarized dust emission, we detect polarization at the 3-sigma level when averaging the emission across the entire disk. The corresponding polarization fraction is 0.51%. The polarization position angle 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. We find that k-RAT is the likely mechanism producing the polarized emission in β Pic.

Free Research Field

Astronomy

Academic Significance and Societal Importance of the Research Achievements

A debris disk is very much like the Kuiper Belt in our own (very old, advanced) solar system. Understanding the behavior of material in a debris disk like Beta Pic therefore helps us understand our own Solar System better.