Grain Size Constraints on Hl Tau With Polarization Signature

Kataoka, Akimasa; Muto, Takayuki; Momose, Munetake; Tsukagoshi, Takashi; Dullemond, C. P.

doi:10.3847/0004-637x/820/1/54

Cited by 117 publications

(161 citation statements)

References 63 publications

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“…These new observations are enabling not only studies of polarization at the scale of protoplanetary disks (where the polarization may be due to a combination of thermal dust emission and scattering: see Kataoka et al 2015Kataoka et al , 2016aYang et al 2016b,a) but are also producing magnetic field maps with far more independent polarization detections across each individual source. These latter maps can be used to study the interplay between magnetic fields and turbulence in low-mass star-forming cores; because of limited image sensitivities, previous interferometric studies have mainly focused on high-mass star-forming regions (e.g., Houde et al 2016).…”

Section: Discussionmentioning

confidence: 99%

Synthetic Observations of Magnetic Fields in Protostellar Cores

Lee

Hull

Offner

2017

ApJ

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The role of magnetic fields in the early stages of star formation is not well constrained. In order to discriminate between different star formation models, we analyze 3D magnetohydrodynamic simulations of low-mass cores and explore the correlation between magnetic field orientation and outflow orientation over time. We produce synthetic observations of dust polarization at resolutions comparable to millimeter-wave dust polarization maps observed by CARMA and compare these with 2D visualizations of projected magnetic field and column density. Cumulative distribution functions of the projected angle between the magnetic field and outflow show different degrees of alignment in simulations with differing mass-to-flux ratios. The distribution function for the less magnetized core agrees with observations finding random alignment between outflow and field orientations, while the more magnetized core exhibits stronger alignment. We find that fractional polarization increases when the system is viewed such that the magnetic field is close to the plane of the sky, and the values of fractional polarization are consistent with observational measurements. The simulation outflow, which reflects the underlying angular momentum of the accreted gas, changes direction significantly over the first ∼ 0.1 Myr of evolution. This movement could lead to the observed random alignment between outflows and the magnetic fields in protostellar cores.

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Section: Discussionmentioning

confidence: 99%

Synthetic Observations of Magnetic Fields in Protostellar Cores

Lee

Hull

Offner

2017

ApJ

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“…A radial magnetic field pattern is derived from an azimuthal polarization pattern, assuming that the polarization arises from magnetically aligned dust grains (i.e., the magnetic field orientations are perpendicular to the polarization orientations, as was assumed in Figures 1 and 2 and described in Section 1). However, an azimuthal polarization pattern can also arise from self-scattering of dust emission from a face-on (or slightly inclined) protoplanetary disk: recent theoretical work has shown that, depending on the combination of dust density, dust-grain growth, optical depth, disk inclination, and resolution of observations, polarization from scattering in disks could contribute to the polarized emission at millimeter wavelengths, perhaps even eclipsing the signal from magnetically aligned dust grains (Kataoka et al 2015(Kataoka et al , 2016aPohl et al 2016;Yang et al 2016aYang et al , 2016bYang et al , 2017. There is now potential evidence for this dust scattering effect from ALMA observations (Kataoka et al 2016b); other high-resolution polarization observations by CARMA and the Karl G. Jansky Very Large Array (VLA; Stephens et al 2014;Cox et al 2015;Fernández-López et al 2016) may also be consistent with self-scattered dust emission.…”

Section: Gravitational Infall or Dust Scatteringmentioning

confidence: 99%

ALMA Observations of Dust Polarization and Molecular Line Emission from the Class 0 Protostellar Source Serpens SMM1

Hull

Girart

Tychoniec

et al. 2017

ApJ

113

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We present high angular resolution dust polarization and molecular line observations carried out with the Atacama Large Millimeter/submillimeter Array (ALMA) toward the Class 0 protostar Serpens SMM1. By complementing these observations with new polarization observations from the Submillimeter Array (SMA) and archival data from the Combined Array for Research in Millimeter-wave Astronomy (CARMA) and the James Clerk Maxwell Telescopes (JCMT), we can compare the magnetic field orientations at different spatial scales. We find major changes in the magnetic field orientation between large (∼0.1 pc) scales-where the magnetic field is oriented E-W, perpendicular to the major axis of the dusty filament where SMM1 is embedded-and the intermediate and small scales probed by CARMA (∼1000 au resolution), the SMA (∼350 au resolution), and ALMA (∼140 au resolution). The ALMA maps reveal that the redshifted lobe of the bipolar outflow is shaping the magnetic field in SMM1 on the southeast side of the source; however, on the northwestern side and elsewhere in the source, lowvelocity shocks may be causing the observed chaotic magnetic field pattern. High-spatial-resolution continuum and spectral-line observations also reveal a tight (∼130 au) protobinary system in SMM1-b, the eastern component of which is launching an extremely high-velocity, one-sided jet visible in both =  (J CO 2 1) and =  (J SiO 5 4); however, that jet does not appear to be shaping the magnetic field. These observations show that with the sensitivity and resolution of ALMA, we can now begin to understand the role that feedback (e.g., from protostellar outflows) plays in shaping the magnetic field in very young, star-forming sources like SMM1.

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“…This prediction can readily be tested with ALMA observations. ALMA polarization data is available for the transition disk HD 142527 (Kataoka et al 2016a), although its interpretation is complicated by the intrinsic asymmetry in the dust distribution. In any case, the observed pattern does not contradict in any obvious way the expectation that the large millimeter-emitting grains have settled in this evolved disk, although more detailed modeling is required to draw a firmer conclusion.…”

Section: Evolution Of Dust Settling From Polarization Of Inclined Disksmentioning

confidence: 99%

“…Such a config-uration would produce a polarization pattern that appears inconsistent with the pattern observed in HL Tau (Stephens et al 2014). The apparent inconsistency led Yang et al (2016a) to propose that the disk polarization in HL Tau comes from dust scattering, based on Kataoka et al (2015) theory of scattering-induced millimeter polarization (see also Kataoka et al 2016a). Specifically, they show that dust scattering in a disk inclined to the line of sight can naturally explain why the observed polarization vectors are roughly parallel to the minor axis and the distribution of polarized intensity is elongated along the major axis.…”

Section: Introductionmentioning

confidence: 99%

Scattering-produced (sub)millimetre polarization in inclined discs: optical depth effects, near–far side asymmetry and dust settling

Yang

Looney

et al. 2017

Monthly Notices of the Royal Astronomical Society

120

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Disk polarization at (sub)millimeter wavelengths is being revolutionized by ALMA observationally, but its origin remains uncertain. Dust scattering was recently recognized as a potential contributor to polarization, although its basic properties have yet to be thoroughly explored. Here, we quantify the effects of optical depth on the scattering-induced polarization in inclined disks through a combination of analytical illustration, approximate semi-analytical modeling using formal solution to the radiative transfer equation, and Monte Carlo simulations. We find that the near-side of the disk is significantly brighter in polarized intensity than the far-side, provided that the disk is optically thick and that the scattering grains have yet to settle to the midplane. This asymmetry is the consequence of a simple geometric effect: the near-side of the disk surface is viewed more edge-on than the far-side. It is a robust signature that may be used to distinguish the scattering-induced polarization from that by other mechanisms, such as aligned grains. The asymmetry is weaker for a geometrically thinner dust disk. As such, it opens an exciting new window on dust settling. We find anecdotal evidence from dust continuum imaging of edge-on disks that large grains are not yet settled in the youngest (Class 0) disks, but become more so in older disks. This trend is corroborated by the polarization data in inclined disks showing that younger disks have more pronounced near-far side asymmetry and thus less grain settling. If confirmed, the trend would have far-reaching implications for grain evolution and, ultimately, the formation of planetesimals and planets.

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Grain Size Constraints on Hl Tau With Polarization Signature

Cited by 117 publications

References 63 publications

Synthetic Observations of Magnetic Fields in Protostellar Cores

Synthetic Observations of Magnetic Fields in Protostellar Cores

ALMA Observations of Dust Polarization and Molecular Line Emission from the Class 0 Protostellar Source Serpens SMM1

Scattering-produced (sub)millimetre polarization in inclined discs: optical depth effects, near–far side asymmetry and dust settling

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