Open AccessMagnetic torques between accretion discs and stars
Author(s) -
Torkelsson Ulf
Publication year - 1998
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.1998.01927.x
Subject(s) - physics , astrophysics , accretion (finance) , torque , magnetic field , radius , pulsar , stars , intermediate polar , angular velocity , stellar magnetic field , spin (aerodynamics) , classical mechanics , white dwarf , computer security , coronal mass ejection , quantum mechanics , computer science , solar wind , thermodynamics
I show in this paper that two types of magnetic torques can appear in the interaction between an accretion disc and a magnetic accretor. There is the well‐known torque resulting from the difference in angular velocity between the accretion disc and the star, but in addition there is a torque coming from the interaction between the stellar magnetic field and the disc’s own magnetic field. The latter form of magnetic torque decreases in strength more slowly with increasing radius, and will therefore dominate at large radii. The direction of the disc field is not determined by the difference in angular velocity between the star and the disc as in the Ghosh &38; Lamb model, but rather is a free parameter. The magnetic torque may therefore either spin up or spin down the star, and the torque changes sign if the magnetic field in the disc reverses. I suggest that this mechanism can explain the torque reversals that have been observed in some disc‐fed X‐ray pulsars.