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Astron. Astrophys. 349, L61-L64 (1999)

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Letter to the Editor

Long-term evolution of a dipolar-type magnetosphere interacting with an accretion disk

Christian Fendt and Detlef Elstner

Astrophysikalisches Institut Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany (cfendt,delstner@aip.de

Received 5 July 1999 / Accepted 24 August 1999


The evolution of a stellar dipolar-type magnetosphere interacting with a Keplerian disk is investigated numerically using the ideal MHD ZEUS-3D code in the axisymmetry option. We compute the innermost region around the stellar object using a non-smoothed gravitational potential. The disk is taken as a boundary condition prescribing the mass inflow into the corona. Depending mainly on the magnetic field strength, our simulations last several hundred Keplerian periods of the inner disk. The main result is that the dipolar structure of the magnetic field almost completely disappears. An expanding bubble of hot gas of low density forms disrupting the initial dipolar field structure. A disk wind accelerates within the time limit of the simulation to velocities of about 0.5 the Keplerian speed and potentially may develop into a stationary collimated jet. We argue that non-stationary jet phenomena should probably caused by a time-dependent disk. Simulations with a rotating and a non-rotating star show significant differences. In the case of a rotating star during the very first time steps a high speed outflow along the axis is initiated which does not exist in the case of a non-rotating star.

Key words: Magnetohydrodynamics (MHD) – accretion, accretion disks – ISM: jets and outflows – stars: magnetic fields – stars: mass-loss – stars: pre-main sequence

© European Southern Observatory (ESO) 1999

Online publication: September 13, 1999