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

Free access article

Issue		A&A Volume 420, Number 1, June II 2004


Page(s)		17 - 32
Section		Astrophysical processes
DOI		http://dx.doi.org/10.1051/0004-6361:20034065

A&A 420, 17-32 (2004)
DOI: 10.1051/0004-6361:20034065

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

B. von Rekowski¹ and A. Brandenburg²

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

(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 $2\,{\rm kG}$ 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 $100\,{\rm G}$ , 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.

Key words: ISM: jets and outflows -- accretion, accretion disks -- magnetic fields -- magnetohydrodynamics (MHD)

Offprint request: B. von Rekowski, Brigitta.vonRekowski@astro.uu.se

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