Turbulent accretion disk dynamos ?
Abstract
We present numerical results for mean-field α^2OMEGA- dynamos in an accretion disk. We first study the linear case in both disks with constant thickness and disks with radially increasing thickness. The preferred mode is dipolar for a thick disk, but quadrupolar for a thin one. The quadrupolar mode generates a magnetic torque that transports angular momentum outwards. The role of the geometrical distribution of both the α-effect and the magnetic diffusivity in the disk is considered for thin disks. It is found that the parity of the most easily excited mode is unaffected, albeit the distribution of the magnetic field and torque change in such a way that a larger fraction of the field and the torque appears in regions with small diffusivity. For some interesting cases we study nonlinear effects like α-quenching and magnetic buoyancy. These effects can affect significantly the magnetic field distribution, compared to the linear case. A transition to chaotic behaviour is found for α-quenching when α is negative in the upper part of the disk.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- March 1994
- Bibcode:
- 1994A&A...283..677T
- Keywords:
-
- Accretion Disks;
- Active Galaxies;
- Cataclysmic Variables;
- Computational Astrophysics;
- Dynamo Theory;
- Magnetohydrodynamic Turbulence;
- Mathematical Models;
- Novae;
- Plasma Jets;
- Stellar Magnetic Fields;
- Stellar Models;
- Angular Momentum;
- Chaos;
- Computerized Simulation;
- Linearity;
- Magnetic Dipoles;
- Magnetohydrodynamics;
- Nonlinearity;
- Quadrupoles;
- Astrophysics