2022 Fiscal Year Annual Research Report
Using ALMA to understand the origin of dust polarization in the Beta Pic debris disk
Project/Area Number |
20K14527
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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)
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Project Period (FY) |
2020-04-01 – 2023-03-31
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Keywords | Polarization / Debris disks / Dust |
Outline of Annual Research Achievements |
The main result of this KAKENHI grant is the publication of the paper regarding the observations of low-level polarization in the Beta Pic debris disk. In the paper, we present 870 μm Atacama Large Millimeter/submillimeter Array polarization observations of thermal dust emission from the iconic, edge-on debris disk β Pic. 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% +/- 0.19%. 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. 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 β 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.
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[Journal Article] Polarization from Aligned Dust Grains in the β Pic Debris Disk2022
Author(s)
Hull, Charles L. H.; Yang, Haifeng; Cortes, Paulo C.; Dent, William R. F.; Kral, Quentin; Li, Zhi-Yun; Le Gouellec, Valentin J. M.; Hughes, A. Meredith; Milli, Julien; Teague, Richard; Wyatt, Mark C.
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Journal Title
The Astrophysical Journal
Volume: 930
Pages: 49
DOI
Peer Reviewed / Open Access / Int'l Joint Research