Session 113 - Old Worn-Out Stars.
Oral session, Thursday, January 16
Piers 2/3,

## [113.06] The interaction of a stellar magnetic field with a turbulent accretion disk

A. Bardou (Strasbourg)

First, a modelisation of turbulence in accretion disks is made using the macroscopic argument that the turbulence level must be such that it adjusts the accretion rate of matter. In such a case, the obtained viscosity law is comparable to the \alpha-prescription of Shakura amp; Sunyaev with \alpha = 0.04.

Then, the interaction between a turbulent accretion disk and a stellar magnetic field is studied. This interaction leads to a very large inflation and expulsion of the non-magnetospheric magnetic flux (magnetic flux threading the disk) towards larger radii. This inflation is demonstrated using three different and complementary methods. First a constraint on the magnetic flux distribution is obtained analytically. Then, a numerical calculation stresses the amplitude of the phenomenon. Finally, a self-similar calculation of the magnetic configuration is made.

The work will be extended to the boundary layer between the magnetopause and the disk.