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Dust Polarization toward Embedded Protostars in Ophiuchus with ALMA. II. IRAS 16293-2422
Sadavoy, Sarah I.,Myers, Philip C.,Stephens, Ian W.,Tobin, John,Kwon, Woojin,Segura-Cox, Dominique,Henning, Thomas,Commerç,on, Benoî,t,Looney, Leslie American Astronomical Society 2018 The Astrophysical journal Vol.869 No.2
Dust Polarization toward Embedded Protostars in Ophiuchus with ALMA. I. VLA 1623
Sadavoy, Sarah I.,Myers, Philip C.,Stephens, Ian W.,Tobin, John,Commerç,on, Benoî,t,Henning, Thomas,Looney, Leslie,Kwon, Woojin,Segura-Cox, Dominique,Harris, Robert American Astronomical Society 2018 The Astrophysical journal Vol.859 No.2
<P>We present high-resolution (similar to 30 au) ALMA Band 6 dust polarization observations of VLA 1623. The VLA 1623 data resolve compact similar to 40 au inner disks around the two protobinary sources, VLA 1623-A and VLA 1623-B, and also an extended similar to 180 au ring of dust around VLA 1623-A. This dust ring was previously identified as a large disk in lower-resolution observations. We detect highly structured dust polarization toward the inner disks and the extended ring with typical polarization fractions similar to 1.7% and similar to 2.4%, respectively. The two components also show distinct polarization morphologies. The inner disks have uniform polarization angles aligned with their minor axes. This morphology is consistent with expectations from dust scattering. By contrast, the extended dust ring has an azimuthal polarization morphology not previously seen in lower-resolution observations. We find that our observations are well-fit by a static, oblate spheroid model with a flux-frozen, poloidal magnetic field. We propose that the polarization traces magnetic grain alignment likely from flux freezing on large scales and magnetic diffusion on small scales. Alternatively, the azimuthal polarization may be attributed to grain alignment by the anisotropic radiation field. If the grains are radiatively aligned, then our observations indicate that large (similar to 100 mu m) dust grains grow quickly at large angular extents. Finally, we identify significant proper motion of VLA 1623 using our observations and those in the literature. This result indicates that the proper motion of nearby systems must be corrected for when combining ALMA data from different epochs.</P>
A First Look at BISTRO Observations of the <i>ρ</i> Oph-A core
Kwon, Jungmi,Doi, Yasuo,Tamura, Motohide,Matsumura, Masafumi,Pattle, Kate,Berry, David,Sadavoy, Sarah,Matthews, Brenda C.,Ward-Thompson, Derek,Hasegawa, Tetsuo,Furuya, Ray S.,Pon, Andy,Francesco, Jame American Astronomical Society 2018 The Astrophysical Journal Vol.859 No.1
Magnetic Fields toward Ophiuchus-B Derived from SCUBA-2 Polarization Measurements
Soam, Archana,Pattle, Kate,Ward-Thompson, Derek,Lee, Chang Won,Sadavoy, Sarah,Koch, Patrick M.,Kim, Gwanjeong,Kwon, Jungmi,Kwon, Woojin,Arzoumanian, Doris,Berry, David,Hoang, Thiem,Tamura, Motohide,Le American Astronomical Society 2018 The Astrophysical journal Vol.861 No.1
<P>We present the results of dust emission polarization measurements of Ophiuchus-B (Oph-B) carried out using the Submillimetre Common-User Bolometer Array 2 (SCUBA-2) camera with its associated polarimeter (POL-2) on the James Clerk Maxwell Telescope in Hawaii. This work is part of the B-fields in Star-forming Region Observations survey initiated to understand the role of magnetic fields in star formation for nearby star-forming molecular clouds. We present a first look at the geometry and strength of magnetic fields in Oph-B. The field geometry is traced over similar to 0.2 pc, with clear detection of both of the sub-clumps of Oph-B. The field pattern appears significantly disordered in sub-clump Oph-B1. The field geometry in Oph-B2 is more ordered, with a tendency to be along the major axis of the clump, parallel to the filamentary structure within which it lies. The degree of polarization decreases systematically toward the dense core material in the two sub-clumps. The field lines in the lower density material along the periphery are smoothly joined to the large-scale magnetic fields probed by NIR polarization observations. We estimated a magnetic field strength of 630 +/- 410 mu G in the Oph-B2 sub-clump using a Davis-Chandrasekhar-Fermi analysis. With this magnetic field strength, we find a mass-to-flux ratio lambda = 1.6 +/- 1.1, which suggests that the Oph-B2 clump is slightly magnetically supercritical.</P>
Harris, Robert J.,Cox, Erin G.,Looney, Leslie W.,Li, Zhi-Yun,Yang, Haifeng,Ferná,ndez-Ló,pez, Manuel,Kwon, Woojin,Sadavoy, Sarah,Segura-Cox, Dominique,Stephens, Ian,Tobin, John American Astronomical Society 2018 The Astrophysical journal Vol.861 No.2
<P>We present high-sensitivity (sigma(I) similar to 0.2-0.5 mJy, sigma(QU) similar to 0.05 mJy), high-resolution (similar to 0.'' 12-0.'' 2) observations of polarized 872 mu m dust emission from the young multiple system VLA 1623 in rho Ophiuchus and the protostar L1527 in Taurus. We detect the circumstellar material of VLA 1623A, the extended Keplerian disk surrounding VLA 1623A that we call VLA 1623CBdisk, VLA 1623B, VLA 1623W, and L1527 strongly in the polarized emission, at the similar to 1%-3% level. We spatially resolve VLA 1623A into two sources, VLA 1623Aa and VLA 1623Ab, separated by similar to 30 au and located within a cavity of radius similar to 50 au within the circumbinary Keplerian disk, as well as the edge-on disk of VLA 1623W. The polarization angle of the emission is uniform across each protostellar source and nearly coincides with each disk's minor axis. The offsets between the minor axis position angle and the polarization angle are not uniformly distributed at the P less than or similar to 2 x 10(-4) level. The circumbinary disk surrounding VLA 1623Aab is azimuthally symmetrically polarized. Each compact source's emission is partially optically thick (tau greater than or similar to 1) at 872 mu m, complicating interpretations of polarization involving aligned grains. We find evidence against alignment by radiative flux in each source, particularly in the edge-on VLA 1623W and L1527. We detect astrometric offsets between the polarized emission and the total intensity in VLA 1623Aa, VLA 1623Ab, and VLA 1623B, as predicted if self-scattering in the optically thick limit operates. We conclude that self-scattering is likely responsible for disk-scale polarization at 872 mu m in these systems.</P>