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Astron. Astrophys. 349, 1003-1016 (1999)

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An accretion-ejection instability in magnetized disks

M. Tagger 1 and R. Pellat 2

1 DSM/DAPNIA/Service d'Astrophysique (CNRS URA 2052), CEA Saclay, F-91191 Gif-sur-Yvette, France
2 Centre de Physique Théorique, Ecole Polytechnique, Palaiseau, France

Received 12 January 1999 / Accepted 21 July 1999


We present an instability occurring in the inner part of disks threaded by a moderately strong vertical (poloidal) magnetic field. Its mechanism is such that a spiral density wave in the disk, driven by magnetic stresses (rather than self-gravity as in galactic spirals), becomes unstable by exchanging angular momentum with a Rossby vortex it generates at its corotation radius. This angular momentum can then "leak" as Alfven waves emitted toward the corona of the disk thus providing, as an element of the accretion process, an energetic source for a wind or a jet. As galactic spirals, this instability forms low azimuthal wavenumber, standing spiral patterns which might provide an explanation for low-frequency QPOs in low-mass X-ray binaries.

Key words: accretion, accretion disks – instabilities – Magnetohydrodynamics (MHD) – waves – galaxies: jets

Send offprint requests to: M. Tagger (tagger@cea.fr)

© European Southern Observatory (ESO) 1999

Online publication: September 13, 1999