Outflows and accretion in a star-disc system with stellar magnetosphere and disc dynamo

¹ Department of Astronomy & Space Physics, Uppsala University, Box 515, 751 20 Uppsala, Sweden
² NORDITA, Blegdamsvej 17, 2100 Copenhagen Ø, Denmark

Corresponding author: B. von Rekowski, Brigitta.vonRekowski@astro.uu.se

Received: 10 July 2003
Accepted: 3 March 2004

Abstract

The interaction between a protostellar magnetosphere and a surrounding dynamo-active accretion disc is investigated using an axisymmetric mean-field model. In all models investigated, the dynamo-generated magnetic field in the disc arranges itself such that in the corona, the field threading the disc is anti-aligned with the central dipole so that no X-point forms. When the magnetospheric field is strong enough (stellar surface field strength around or larger), accretion happens in a recurrent fashion with periods of around 15 to 30 days, which is somewhat longer than the stellar rotation period of around 10 days. In the case of a stellar surface field strength of at least a few , the star is being spun up by the magnetic torque exerted on the star. The stellar accretion rates are always reduced by the presence of a magnetosphere which tends to divert a much larger fraction of the disc material into the wind. Both, a pressure-driven stellar wind and a disc wind form. In all our models with disc dynamo, the disc wind is structured and driven by magneto-centrifugal as well as pressure forces.