The tidally induced warping, precession and truncation of accretion discs

Details The tidally induced warping, precession and truncation of accretion discs The tidally induced warping, precession and truncation of accretion discs

Dec 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997phdt........23l&link_type=abstract

PhD thesis, Queen Mary and Westfield College, London, (1997)

Computer Science

Sound

3

Scientific paper

A three-dimensional smoothed particle hydrodynamics code is applied to the study of gaseous accretion discs. The numerical accretion disc models are developed and tested. These models are used to investigate the disc response to tidal forcing, for various scenarios, and also to study the stability of self-gravitating discs. The initial consideration is of a circular orbit binary system in which one of the component stars carries a non-self-gravitating accretion disc and the other is naked and circulating at some inclination to the midplane of the disc. The degree of disc warping and global precession is determined analytically, in a linear perturbation treatment of the fluid equations, and these results are compared with simulations. The disc response is studied as a function of binary mass ratio, separation, inclination and disc thickness. It is demonstrated that differentially rotating discs can precess approximately as rigid bodies provided that the precessional timescale is sufficiently long when compared with the sound-crossing timescale for the disc. For circumbinary discs it is found that if the disc is sufficiently extended then the precession frequency tends to zero and a small warp is maintained at the inner regions. For parabolic encounters it is found that a small precessional displacement effectively tilts the disc midplane. In all cases it is found that tidal truncation can operate effectively in highly inclined systems, although at a lower level than for coplanar systems. For the self-gravitating disc models, a simple cooling algorithm is developed and incorporated into the hydrodynamics code. It is found that the usual condition for instability to non-axisymmetric perturbations is insufficient to also ensure fragmentation, and instead a higher level of instability than is usually considered appears to be required. Relevant astrophysical applications of the results are discussed. These include: the precession of jets in X-ray binary systems and star formation regions, the observational appearance of protoplanetary discs in the Orion Nebula, and the origins of supermassive extrasolar planets.

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