Buoyant magnetic flux ropes in a magnetized stellar envelope

Idealized numerical 2.5-D MHD simulations

¹ Copenhagen University Library, Nørre allé 49, 2200 Copenhagen N, Denmark e-mail: dorch@astro.ku.dk
² The Niels Bohr Institute, Copenhagen University, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark

Received: 15 June 2006
Accepted: 15 September 2006

Abstract

Context.The context of this paper is buoyant toroidal magnetic flux ropes, which is a part of flux tube dynamo theory and the framework of solar-like magnetic activity.

Aims.The aim is to investigate how twisted magnetic flux ropes interact with a simple magnetized stellar model envelope – a magnetic “convection zone” – especially to examine how the twisted magnetic field component of a flux rope interacts with a poloidal magnetic field in the convection zone.

Methods.Both the flux ropes and the atmosphere are modelled as idealized 2.5-dimensional concepts using high resolution numerical magneto-hydrodynamic (MHD) simulations.

Results.It is illustrated that twisted toroidal magnetic flux ropes can interact with a poloidal magnetic field in the atmosphere to cause a change in both the buoyant rise dynamics and the flux rope's geometrical shape. The details of these changes depend primarily on the polarity and strength of the atmospheric field relative to the field strength of the flux rope. It is suggested that the effects could be verified observationally.