An investigation of magnetic field distortions in accretion discs around neutron stars. II. Analysis of the toroidal field component
| Autor: | J. C. Miller, L. Naso |
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| Jazyk: | angličtina |
| Rok vydání: | 2011 |
| Předmět: |
Accretion
Magnetohydrodynamics (MHD) FOS: Physical sciences Astrophysics Pulsar Settore FIS/05 - Astronomia e Astrofisica Millisecond pulsar Physics::Plasma Physics Solar and Stellar Astrophysics (astro-ph.SR) Physics High Energy Astrophysical Phenomena (astro-ph.HE) accretion disks Stellar magnetic field Astronomy and Astrophysics Accretion accretion disks Computational physics Magnetic field Turbulence Neutron star Dipole Astrophysics - Solar and Stellar Astrophysics Space and Planetary Science Magnetic fields Vector field Induction equation Astrophysics - High Energy Astrophysical Phenomena |
| Popis: | Millisecond pulsars are believed to be old pulsars spun up by a surrounding accretion disc. Magnetic fields are thought to play a leading role in this, both by determining the location of the inner edge of the disc and by exerting an additional torque on the star (as a result of the interaction between the stellar magnetic field and the disc plasma motion, which creates a toroidal component B_phi). In some well-known analytic models, developed in the 1980s, the B_phi profile was taken to be proportional to the relative angular velocity between the disc plasma and the neutron star, multiplied by a vertical dipolar field. The present work stands in the line of improving those models, suggesting a new profile for B. In a previous paper, we discussed the poloidal component of the magnetic field and here we consider the toroidal component, again making the kinematic approximation and looking for steady solutions of the induction equation for axisymmetric models. The poloidal magnetic field is not assumed to be dipolar and the poloidal velocity field is not taken to be zero everywhere. We also do not use the thin disc approximation to simplify the induction equation but instead solve it numerically in full 2D. The profile obtained in the earlier analytic models is shown to have very limited validity and a more general semi-analytic solution is proposed. Comment: Published in A&A - 13 pages, 17 figures and one table - Changes with respect to previous version: added comment on magnetic Prandtl number; minor modifications (added comment on mean field induction equation, removed confusion about the names of some variables, updated references, merged two figures, removed references from abstract) |
| Databáze: | OpenAIRE |
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