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Title:
Stringent Limits on the Polarized Submillimeter Emission from Protoplanetary Disks
Authors:
Hughes, A. Meredith; Wilner, David J.; Cho, Jungyeon; Marrone, Daniel P.; Lazarian, Alexandre; Andrews, Sean M.; Rao, Ramprasad
Affiliation:
AA(Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA ), AB(Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA ), AC(Department of Astronomy and Space Science, Chungnam National University, Daejeon, Republic of Korea ; University of Wisconsin, Department of Astronomy, 475 N. Charter Street, Madison, WI 53706, USA ; ), AD(The University of Chicago, The Kavli Institute for Cosmological Physics, 933 East 56th Street, Chicago, IL 60637, USA ; Jansky Fellow ; ), AE(University of Wisconsin, Department of Astronomy, 475 N. Charter Street, Madison, WI 53706, USA ), AF(Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA ; Hubble Fellow; ), AG(Hubble Fellow )
Publication:
The Astrophysical Journal, Volume 704, Issue 2, pp. 1204-1217 (2009). (ApJ Homepage)
Publication Date:
10/2009
Origin:
IOP
ApJ Keywords:
circumstellar matter, planetary systems: protoplanetary disks, polarization, stars: individual: HD 163296 TW Hydrae
DOI:
10.1088/0004-637X/704/2/1204
Bibliographic Code:
2009ApJ...704.1204H

Abstract

We present arcsecond-resolution Submillimeter Array (SMA) polarimetric observations of the 880 μm continuum emission from the protoplanetary disks around two nearby stars, HD 163296 and TW Hydrae. Although previous observations and theoretical work have suggested that a 2%-3% polarization fraction should be common for the millimeter continuum emission from such disks, we detect no polarized continuum emission above a 3σ upper limit of 7 mJy in each arcsecond-scale beam, or <1% in integrated continuum emission. We compare the SMA upper limits with the predictions from the exploratory Cho & Lazarian model of polarized emission from T Tauri disks threaded by toroidal magnetic fields, and rule out their fiducial model at the ~10σ level. We explore some potential causes for this discrepancy, focusing on model parameters that describe the shape, magnetic field alignment, and size distribution of grains in the disk. We also investigate related effects like the magnetic field strength and geometry, scattering off of large grains, and the efficiency of grain alignment, including recent advances in grain alignment theory, which are not considered in the fiducial model. We discuss the impact each parameter would have on the data and determine that the suppression of polarized emission plausibly arises from rounding of large grains, reduced efficiency of grain alignment with the magnetic field, and/or some degree of magnetic field tangling (perhaps due to turbulence). A poloidal magnetic field geometry could also reduce the polarization signal, particularly for a face-on viewing geometry like the TW Hya disk. The data provided here offer the most stringent limits to-date on the polarized millimeter-wavelength emission from disks around young stars.
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