Magnetic Fields in T Tauri Disks A. Meredith Hughes Wesleyan University What Millimeter Polarimetry...
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Transcript of Magnetic Fields in T Tauri Disks A. Meredith Hughes Wesleyan University What Millimeter Polarimetry...
![Page 1: Magnetic Fields in T Tauri Disks A. Meredith Hughes Wesleyan University What Millimeter Polarimetry Can Tell Us Chat Hull, David Wilner, Sean Andrews,](https://reader036.fdocuments.net/reader036/viewer/2022070306/5517a52f55034645368b5c2a/html5/thumbnails/1.jpg)
Magnetic Fields in T Tauri Disks
A. Meredith HughesWesleyan University
What Millimeter Polarimetry Can Tell Us
Chat Hull, David Wilner, Sean Andrews, Jungyeon Cho, Dick Plambeck, Dan Marrone, Ram Rao, Alex Lazarian
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Circumstellar disks as accretion disks
Balbus & Hawley (1991), Stone et al. (2000)
Theories of disk evolution generally invoke MRI-driven turbulence as source of anomalous
viscosity.
The mass distribution in a disk changes over time as material is transported by viscosity of unspecified
origin.
What is observable?•B-field needed to drive MRI
Aligned dust grains should generate polarized emission
•Turbulence that generates viscosityNonthermal widths of molecular lines
HD 163296 CO(3-2)
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History: Single-dish observations
Tentative (3) 3% polarization detection
in two T Tauri disks with JCMT
Tamura et al. (1999)
Previously: HL Tau and an upper limit on GG
Tau
Tamura et al. (1995)
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First realistic models of polarized emission from disks predict 2-3% polarization at mm wavelengths•Grains aligned by radiative torque•Chiang & Goldreich disk model•Toroidal B-field
Cho & Lazarian (2007)
Theory: Predicting Resolved Observations
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Instrumentation: The SMA Polarimeter
Marrone & Rao (2008)
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New Observations
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HD 163296
Hughes et al. (2009)
Round 1: Two Disks with the SMA
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TW Hya
Hughes et al. (2009)
Round 1: Two Disks with the SMA
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The Plot Thickens:DG Tau at 350 μm
Krejny et al. (2009)
Same source, similar resolution, shorter wavelength…
No polarization!
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Round 2: Plugging the Gaps
And now, the field is a mess!
• Tamura et al. (1995, 1999)– 3σ polarization detections in 2-3 T Tauri
sources– Indicate toroidal magnetic field
• Krejny et al. (2009)– Revisited one source, different wavelength– No polarization
• Hughes et al. (2009)– Two new sources– No polarization
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Round 2: Plugging the GapsH
ughe
s et
al.
(201
3)
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Does size matter?
Two possibilities:
1) JCMT detections were spurious (low-significance, after all…)
2) Continuum emission is polarized only on large (~1000 AU) scales
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A quick word about TADPOL
Hull et al. (2013)
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Model Comparison
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Turning Knobs
Identify model inputs that most strongly affect pol %, given
Stokes I
1) Grain elongation
2) Alignment efficiency
3) Grain size distribution
4) B-field strength
5) B-field regularity
6) Scattering…
Hughes et al. (2009)
Cho & Lazarian (2007)
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The Future: Polarization with ALMA
IF grains are aligned but fields are tangled, then it is worthwhile to push to higher angular resolution < scale height (easier)
IF grains are not aligned, then next best bet may be Zeeman effect in CN, to get los magnetic field (harder)
Falgarone et al. (2008)