4.6 Article

ALMA Observations of Polarized Emission toward the CW Tau and DG Tau Protoplanetary Disks: Constraints on Dust Grain Growth and Settling

Journal

ASTROPHYSICAL JOURNAL LETTERS
Volume 865, Issue 2, Pages -

Publisher

IOP PUBLISHING LTD
DOI: 10.3847/2041-8213/aadf87

Keywords

ISM: jets and outflows; polarization; protoplanetary disks

Funding

  1. MINECO (Spain) [AYA2014-57369-C3, AYA2017-84390-C2]
  2. EU-Horizon-2020/MSC grant [664931]
  3. project PRIN-INAF/2016 GENESIS-SKA
  4. Italian Ministero dell'Istruzione, Universita e Ricerca, through the grant Progetti Premiali 2012/iALMA [CUP-C52I13000140001]
  5. Italian Ministero dell'Istruzione, Universita e Ricerca, through the grant 2017/FRONTIERA [CUP-C61I15000000001]
  6. Italian Ministero dell'Istruzione, Universita e Ricerca, through the grant SIR [RBSI14ZRHR]
  7. Deutsche Forschungsgemeinschaft (DFG
  8. German Research Foundation) [FOR 2634/1 TE 1024/1-1]
  9. DFG cluster of excellence Origin and Structure of the Universe
  10. project ADS/JAO.ALMA [2015.1.00840.S]

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We present polarimetric data of CW Tau and DG Tau, two well-known Class II disk/jet systems, obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) at 870 mu m and 0 2 average resolution. In CW Tau, the total and polarized emission are both smooth and symmetric, with polarization angles almost parallel to the minor axis of the projected disk. In contrast, DG Tau displays a structured polarized emission, with an elongated brighter region in the disk's near side and a belt-like feature beyond about 0 3 from the source. At the same time, the total intensity is spatially smooth, with no features. The polarization pattern, almost parallel to the minor axis in the inner region, becomes azimuthal in the outer belt, possibly because of a drop in optical depth. The polarization fraction has average values of 1.2% in CW Tau and 0.4% in DG Tau. Our results are consistent with polarization from self-scattering of the dust thermal emission. In this hypothesis, the maximum size of the grains contributing to polarization is in the range 100-150 mu m for CW Tau and 50-70 mu m for DG Tau. The polarization maps combined with dust opacity estimates indicate that these grains are distributed in a geometrically thin layer in CW Tau, representing a settling in the disk midplane. Meanwhile, such settling is not yet apparent for DG Tau. These results advocate polarization studies as a fundamental complement to total emission observations, in investigations of the structure and the evolution of protoplanetary disks.

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