Journal Article

Oscillations of magnetohydrodynamic shock waves on the surfaces of T Tauri stars

A. V. Koldoba, G. V. Ustyugova, 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 388, issue 1, pages 357-366
Published in print July 2008 | ISSN: 0035-8711
Published online July 2008 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2008.13394.x
Oscillations of magnetohydrodynamic shock waves on the surfaces of T Tauri stars

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This work treats the matter deceleration in a magnetohydrodynamic radiative shock wave at the surface of a star. The problem is relevant to classical T Tauri stars where infalling matter is channelled along the star's magnetic field and stopped in the dense layers of photosphere. A significant new aspect of this work is that the magnetic field has an arbitrary angle with respect to the normal to the star's surface. We consider the limit where the magnetic field at the surface of the star is not very strong in the sense that the inflow is super-Alfvénic. In this limit, the initial deceleration and heating of plasma (at the entrance to the cooling zone) occurs in a fast magnetohydrodynamic shock wave. To calculate the intensity of radiative losses we use ‘real’ and ‘power-law’ radiative functions. We determine the stability/instability of the radiative shock wave as a function of parameters of the incoming flow: velocity, strength of the magnetic field, and its inclination to the surface of the star. In a number of simulation runs with the ‘real’ radiative function, we find a simple criterion for stability of the radiative shock wave. For a wide range of parameters, the periods of oscillation of the shock wave are of the order of 0.02–0.2 s.

Keywords: accretion, accretion discs; instabilities; MHD; shock waves; stars: magnetic fields; stars: oscillations

Journal Article.  7142 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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