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On the Torque Exerted by a Magnetically Threaded Accretion Disk

Reference:1979ApJ...232..259G apj449L153

Reporter: Xu Kun

2015.3.17

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Outline

*The GL79a model

*Evaluation of the torque

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The Ghosh & Lamb (1979a,b) Model for Disk-Field Interaction

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The GL79a Model

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Structure of the Transition Zone

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Equations of the Boundary LayerRadial-Structure Vertical-Structure

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Dimensionless

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Rewrite the Equations in Nondimensional Form

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Examples of Boundary-Layer Structure (1)0.3s

0 0.5

2.5

2b

p

C

C

0 1

1.5

1.5b

p

C

C

0 2

2

1.5b

p

C

C

0 4

4

1b

p

C

C

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Examples of Boundary-Layer Structure (2)0 1 2.5 2b pC C ， ，

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Existence of Maximum Fastness

max 1

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Evaluation of the torque

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The Torque

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Discussion

• ranging from 0.875-0.950• The most plausible of the three is the third

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