Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004sf2a.conf..385p&link_type=abstract
SF2A-2004: Semaine de l'Astrophysique Francaise, meeting held in Paris, France, June 14-18, 2004. Edited by F. Combes, D. Barret
Astronomy and Astrophysics
Astrophysics
Scientific paper
Accretion discs are very widespread in the Universe. One observes them in many astrophysical objects such as the active nuclei of galaxies, the binary systems including a compact object, or around stars in formation. However, the mechanism responsible for this accretion towards the central object is still badly known. Indeed, molecular viscosity alone is too weak to explain the accretion rates observed. Nevertheless, the discovery of the quasi-periodic oscillations (QPOs) in the mid 80' offers a new appropriate probe of the accretion discs in their internal regions. Certain models such as for example the relativistic precession or the beat frequency at the sonic point or at the magnetospheric radius were advanced to explain this phenomenon. However, those require either the presence of a magnetic field dragged by the rotation of the accreting source or effects of pure General Relativity. However recent observations showed a correlation between QPOs of white dwarfs, neutron stars and black holes. If one accepts the idea of a common origin for these QPOs, one is led to reject the existing models. In this presentation, I will propose a new model using a nonaxisymmetric component, in rotation either in the gravitational field or in the magnetic field of the accreting star. In a first part, I will show that the linear stability analysis of a disc evolving in such a structure predicts the existence of 3 instability types: a resonance of corotation, a parametric resonance and a resonance of forcing. In a second part, these results will be generalised with 2D simulations using pseudo-spectral methods. Lastly, I will discuss the observational consequences of these instabilities on the light curves emitted by the disc, allowing later a confrontation with the observations.
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