Journal Article

Three-dimensional simulations of accretion to stars with complex magnetic fields

M. Long, M. M. Romanova and R. V. E. Lovelace

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 386, issue 3, pages 1274-1284
Published in print May 2008 | ISSN: 0035-8711
Published online April 2008 | e-ISSN: 1365-2966 | DOI:
Three-dimensional simulations of accretion to stars with complex magnetic fields

Show Summary Details


Disc accretion to rotating stars with complex magnetic fields is investigated using full 3D magnetohydrodynamic (MHD) simulations. The studied magnetic configurations include superpositions of misaligned dipole and quadrupole fields and off-centre dipoles. The simulations show that when the quadrupole component is comparable to the dipole component, the magnetic field has a complex structure with three major magnetic poles on the surface of the star and three sets of loops of field lines connecting them. A significant amount of matter flows to the quadrupole ‘belt’, forming a ring-like hotspot on the star. If the maximum strength of the magnetic field on the star is fixed, then we observe that the mass accretion rate, the torque on the star and the area covered by hotspots are several times smaller in the quadrupole-dominant cases than in the pure dipole cases. The influence of the quadrupole component on the shape of the hotspots becomes noticeable when the ratio of the quadrupole and dipole field strengths Bq/Bd≳ 0.5. It becomes dominant in determining the shape of the hotspots when Bq/Bd≳ 1. We conclude that if the quadrupole component is larger than the dipole one, then the shape of the hotspots is determined by the quadrupole field component. In the case of an off-centre dipole field, most of the matter flows through a one-armed accretion stream, forming a large hotspot on the surface, with a second much smaller secondary spot. The light curves may have simple, sinusoidal shapes, thus mimicking stars with pure dipole fields. Or, they may be complex and unusual. In some cases, the light curves may be indicators of a complex field, in particular if the inclination angle is known independently. We also note that in the case of complex fields, magnetospheric gaps are often not empty, and this may be important for the survival of close-in exosolar planets.

Keywords: accretion, accretion discs; magnetic fields; MHD; stars: magnetic fields

Journal Article.  8266 words.  Illustrated.

Subjects: Astronomy and Astrophysics

Full text: subscription required

How to subscribe Recommend to my Librarian

Users without a subscription are not able to see the full content. Please, subscribe or login to access all content.