apjThe Astrophysical JournalAPJAstrophys. J.0004-637X1538-4357The American Astronomical Societyapjac602310.3847/1538-4357/ac6023ac6023AAS37249320Interstellar Matter and the Local UniversePolarization from Aligned Dust Grains in the β Pic Debris Disk0000-0002-8975-7573HullCharles L. H.1215chat.hull@nao.ac.jp0000-0002-8537-6669YangHaifeng海峰34hfyang@pku.edu.cn0000-0002-3583-780XCortésPaulo C.25DentWilliam R. F.260000-0001-6527-4684KralQuentin70000-0002-7402-6487LiZhi-Yun80000-0002-5714-799XLe GouellecValentin J. M.69100000-0002-4803-6200HughesA. Meredith110000-0001-9325-2511MilliJulien120000-0003-1534-5186TeagueRichard130000-0001-9064-5598WyattMark C.14 National Astronomical Observatory of Japan, Los Abedules 3085, Of. 701, Vitacura 763 0414, Santiago, Chile; chat.hull@nao.ac.jp Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura, Santiago, Chile Kavli Institute for Astronomy and Astrophysics, Peking University, Yi He Yuan Lu 5, Haidian Qu, Beijing 100871, People’s Republic of China hfyang@pku.edu.cn Institute for Advanced Study, Tsinghua University, Beijing, 100084, People’s Republic of China National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA European Southern Observatory, Alonso de Córdova 3107, Vitacura, Santiago, Chile LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, F-92195, Meudon, France Department of Astronomy, University of Virginia, Charlottesville, VA 22903, USA SOFIA Science Center, Universities Space Research Association, NASA Ames Research Center, Moffett Field, California 94035, USA Université Paris-Saclay, CNRS, CEA, Astrophysique, Instrumentation et Modélisation de Paris-Saclay, F-91191, Gif-sur-Yvette, France Department of Astronomy, Van Vleck Observatory, Wesleyan University, 96 Foss Hill Drive, Middletown, CT 06459, USA Université Grenoble Alpes, IPAG, F-38000 Grenoble, France Center for Astrophysics ∣ Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK

NAOJ Fellow.

0152022030520220305202293014921120221032022213202221032022© 2022. The Author(s). Published by the American Astronomical Society.2022 Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.Abstract

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 ∼3σ level when averaging the emission across the entire disk. The corresponding polarization fraction is P frac = 0.51% ± 0.19%. The polarization position angle χ 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.

unified-astronomy-thesaurushttp://astrothesaurus.org/uat/5A stars5http://astrothesaurus.org/uat/363Debris disks363http://astrothesaurus.org/uat/412Dust continuum emission412http://astrothesaurus.org/uat/808Interferometry808http://astrothesaurus.org/uat/821Interplanetary dust821http://astrothesaurus.org/uat/824Interplanetary magnetic fields824http://astrothesaurus.org/uat/1278Polarimetry1278http://astrothesaurus.org/uat/1647Submillimeter astronomy1647http://astrothesaurus.org/uat/1967Radiative transfer simulations1967http://astrothesaurus.org/uat/2107Theoretical models2107National Science Foundation (NSF)https://doi.org/10.13039/100000001 AST-1815784MEXT ∣ Japan Society for the Promotion of Science (JSPS)https://doi.org/10.13039/501100001691 18K1358620K14527National Aeronautics and Space Administration (NASA)https://doi.org/10.13039/100000104 80NSSC18K1095Research Corporation for Science Advancement (RCSA)https://doi.org/10.13039/100001309 Cottrell Scholar AwardEuropean Southern Observatory (ESO)https://doi.org/10.13039/501100004604 ESO Studentshipccc0004-637X/22/49+16$33.00crossmarkyes