ON TIDALLY INDUCED SHOCKS IN ACCRETION DISKS IN CLOSE BINARY-SYSTEMS

We present linear and non-linear calculations of the tidal interaction of an accretion disc in close binary systems with mass ratios of unit y and one tenth. We consider characteristic Mach numbers of the Kepler ian flow between 10 and 50 and both inviscid discs and discs with an i nternal shear viscosity. We calculate the angular momentum transfer be tween the disc and the companion star and indicate how the excited spi ral density waves can be understood in terms of a linear tidal respons e calculation. In agreement with earlier work it is found that hot, ex tended discs with Mach numbers M less-than-or-equal-to 1 0, such as th ose in close binary T Tauri stars, are subject to strong tidal couplin g with the companion star, whereby the disc loses a sufficient amount of angular momentum through shock dissipation to enable disc matter to accrete on to the central star. For cool discs with Mach numbers M gr eater-than-or-equal-to 25, thought typical for discs in cataclysmic va riable and X-ray binaries, however, the wavelength of the tidal respon se is much shorter than the length-scale of the tidal force so that th e tidal interaction becomes inefficient and, although adequate to trun cate the disc, it produces little wave-driven accretion on to the cent ral star.