3D MHD Simulations of Waves Excited in an Accretion Disk by a Rotating Magnetized Star

R.V.E. Lovelace, M.M. Romanova, E. Bozzo, P. Kretschmar, M. Audard, M. Falanga, C. Ferrigno
2014 EPJ Web of Conferences  
We present results of global 3D MHD simulations of warp and density waves in accretion disks excited by a rotating star with a misaligned dipole magnetic field. A wide range of cases are considered. We find for example that if the star's magnetosphere corotates approximately with the inner disk, then a strong one-arm bending wave or warp forms. The warp corotates with the star and has a maximum amplitude (|z w |/r ∼ 0.3) between the corotation radius and the radius of the vertical resonance. If
more » ... the magnetosphere rotates more slowly than the inner disk, then a bending wave is excited at the disk-magnetosphere boundary, but it does not form a large-scale warp. In this case the angular rotation of the disk [Ω(r, z = 0)] has a maximum as a function of r so that there is an inner region where dΩ/dr > 0. In this region we observe radially trapped density waves in approximate agreement with the theoretical prediction of a Rossby wave instability in this region. a This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Article available at http://www.epj-conferences.org or http://dx.doi.org/10.1051/epjconf/20136405003 where Ω * is the angular velocity of the star. In linear approximation, we suggest that the m−harmonic of this force excites the m−arm wave in the disk. The frequency of this force is mΩ * . Then, for a Keplerian disk, the condition for the Lindblad resonancesω = ±Ω is mΩ * − mΩ = ±Ω, or, r LR = r cr (1 ± 1/m) 2/3 , where r cr = (GM/Ω 2 * ) 1/3 is the corotation radius.
doi:10.1051/epjconf/20136405003 fatcat:wzzjjzyg55awpdf2bzgpjtno24