AN ORDERED MAGNETIC FIELD IN THE PROTOPLANETARY DISK OF AB Aur REVEALED BY MID-INFRARED POLARIMETRY

ABSTRACT Magnetic fields (B-fields) play a key role in the formation and evolution of protoplanetary disks, but their properties are poorly understood due to the lack of observational constraints. Using CanariCam at the 10.4 m Gran Telescopio Canarias, we have mapped out the mid-infrared polarizatio...

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Bibliographic Details
Published in:The Astrophysical journal 2016-11, Vol.832 (1), p.18
Main Authors: Li, Dan, Pantin, Eric, Telesco, Charles M., Zhang, Han, Wright, Christopher M., Barnes, Peter J., Packham, Chris, Mariñas, Naibí
Format: Article
Language:English
Subjects:
Astrophysics
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
Axes of rotation
COSMIC DUST
Disks
GRAIN GROWTH
HERBIG-HARO OBJECTS
Infrared astronomy
INTERMEDIATE INFRARED RADIATION
INTERSTELLAR GRAINS
INTERSTELLAR MAGNETIC FIELDS
LAYERS
LIMITING VALUES
Lofting
Magnetic fields
Planet formation
POLARIMETRY
POLARIZATION
PROBES
Protoplanetary disks
PROTOPLANETS
RESOLUTION
SCATTERING
Space telescopes
STARS
stars: individual (AB Aur)
stars: pre-main sequence
SURFACES
VISCOSITY
WAVELENGTHS
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Summary:ABSTRACT Magnetic fields (B-fields) play a key role in the formation and evolution of protoplanetary disks, but their properties are poorly understood due to the lack of observational constraints. Using CanariCam at the 10.4 m Gran Telescopio Canarias, we have mapped out the mid-infrared polarization of the protoplanetary disk around the Herbig Ae star AB Aur. We detect ∼0.44% polarization at 10.3 m from AB Aur's inner disk (r < 80 au), rising to ∼1.4% at larger radii. Our simulations imply that the mid-infrared polarization of the inner disk arises from dichroic emission of elongated particles aligned in a disk B-field. The field is well ordered on a spatial scale, commensurate with our resolution (∼50 au), and we infer a poloidal shape tilted from the rotational axis of the disk. The disk of AB Aur is optically thick at 10.3 m, so polarimetry at this wavelength is probing the B-field near the disk surface. Our observations therefore confirm that this layer, favored by some theoretical studies for developing magneto-rotational instability and its resultant viscosity, is indeed very likely to be magnetized. At radii beyond ∼80 au, the mid-infrared polarization results primarily from scattering by dust grains with sizes up to ∼1 m, a size indicating both grain growth and, probably, turbulent lofting of the particles from the disk mid-plane.
ISSN:0004-637X
1538-4357
DOI:10.3847/0004-637X/832/1/18