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TRANSCRIPT
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Magnetic Turbulence in Giant Planet Formation
Sarah Keith
Magnetic Fields Workshop 2012
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Accretion onto Giant Planets
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•Planets grow through accretion
•Accretion requires viscosity
•Viscosity from magnetic turbulence is currently the only viable source
•Magnetic turbulence requires a
magnetic field – disk coupling
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Does magnetic turbulence occur?
Do circumplanetary disks couple to magnetic fields?
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Outline
Model Disk Temperature, Density
Degree of Ionisation
Magnetic Field
Magnetic Diffusivity
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Disk model
5/15
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Calculating disk profiles
6/15
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Opacity Law
We solve for the opacity using the measured Bell & Lin 1994 opacity
law
Ice Grains Metal Grains
Molecules
H-Scattering
Bound-free & free-free
Electron Scattering
Be
ll &
Lin
19
94
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Disk Profiles
Midplane Temperature
Scale Height
Surface Density
Opacity
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Temperature Profile
Standard parameter set
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Ionisation Fraction
SOURCE : Thermal ionisation
Potassium –low ionising potential
Hydrogen – abundant
SINK : Dust grains
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Ionisation Model
Hydrogen
Potassium
Dust grains
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Magnetic Field
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Magnetic Diffusivity
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Magnetic Diffusivity
Poorly coupled Well coupled
Ohmic
Hall Ambipolar
Coupling Threshold
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Conclusions
The disk couples out to 40 Jupiter radii
but the rest of the disk is does not couple
No accretion across most of disk
- Other ionising sources?
- Accretion in layers above midplane?
- Viscosity prescription using MHD simulations?
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