Query : 2018A&A...616A..56A

2018A&A...616A..56A - Astronomy and Astrophysics, volume 616A, 56-56 (2018/8-1)

Magnetic field in a young circumbinary disk.


Abstract (from CDS):

Context. Polarized continuum emission at millimeter-to-submillimeter wavelengths is usually attributed to thermal emission from dust grains aligned through radiative torques with the magnetic field. However, recent theoretical work has shown that under specific conditions polarization may arise from self-scattering of thermal emission and by radiation fields from a nearby stellar object.
Aims. We use multi-frequency polarization observations of a circumbinary disk to investigate how the polarization properties change at distinct frequency bands. Our goal is to discern the main mechanism responsible for the polarization through comparison between our observations and model predictions for each of the proposed mechanisms.
Methods. We used the Atacama Large Millimeter/submillimeter Array to perform full polarization observations at 97.5GHz (Band 3), 233GHz (Band 6) and 343.5GHz (Band 7). The ALMA data have a mean spatial resolution of 28AU. The target is the Class I object BHB07-11, which is the youngest object in the Barnard 59 protocluster. Complementary Karl G. Jansky Very Large Array observations at 34.5GHz were also performed and revealed a binary system at centimetric continuum emission within the disk.
Results. We detect an extended and structured polarization pattern that is remarkably consistent between the three bands. The distribution of polarized intensity resembles a horseshoe shape with polarization angles following this morphology. From the spectral index between Bands 3 and 7, we derived a dust opacity index β∼1 consistent with maximum grain sizes larger than expected to produce self-scattering polarization in each band. The polarization morphology and the polarization levels do not match predictions from self-scattering. On the other hand, marginal correspondence is seen between our maps and predictions from a radiation field model assuming the brightest binary component as main radiation source. Previous molecular line data from BHB07-11 indicates disk rotation. We used the DustPol module of the ARTIST radiative transfer tool to produce synthetic polarization maps from a rotating magnetized disk model assuming combined poloidal and toroidal magnetic field components. The magnetic field vectors (i.e., the polarization vectors rotated by 90°) are better represented by a model with poloidal magnetic field strength about three times the toroidal one.
Conclusions. The similarity of our polarization patterns among the three bands provides a strong evidence against self-scattering and radiation fields. On the other hand, our data are reasonably well reproduced by a model of disk with toroidal magnetic field components slightly smaller than poloidal ones. The residual is likely to be due to the internal twisting of the magnetic field due to the binary system dynamics, which is not considered in our model.

Abstract Copyright: © ESO 2018

Journal keyword(s): magnetic fields - polarization - scattering - instrumentation: interferometers - techniques: polarimetric - protoplanetary disks

VizieR on-line data: <Available at CDS (J/A+A/616/A56): list.dat fits/*>

Nomenclature: Paragr. 2.2: [AGP2018] B59 VLA 5a (Nos 5a-5b).

Simbad objects: 10

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Number of rows : 10
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
1 V* HL Tau Or* 04 31 38.5107609312 +18 13 57.859747968   15.89 14.49 14.39   K5 1393 0
2 HD 142527 Ae* 15 56 41.8882637904 -42 19 23.248281828   9.04 8.34     F6III 616 1
3 QSO J1700-2610 QSO 17 00 53.15406418 -26 10 51.7253944   16.50       ~ 106 1
4 LDN 1746 DNe 17 11.3 -27 22           ~ 132 0
5 2MASS J17112317-2724315 ** 17 11 23.17752 -27 24 31.5288           ~ 69 0
6 QSO J1713-2658 QSO 17 13 31.27560863 -26 58 52.5267399   19.65       ~ 39 1
7 NAME the Pipe Nebula DNe 17 30 -25.0           ~ 392 1
8 QSO B1730-130 QSO 17 33 02.70578907 -13 04 49.5482119   18 19.50 18.78 17.39 ~ 1108 1
9 4C 09.57 BLL 17 51 32.81857326 +09 39 00.7284066   17.46 16.78 15.57   ~ 918 1
10 QSO B1921-293 BLL 19 24 51.05595254 -29 14 30.1210248   18.71 18.21 15.07   ~ 837 0

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