Radiative tides in accretion disks

The viscous model for accretion disks encounters difficulties both in providing a source of viscosity and in removing angular momentum from the disk outer edges where it is transported by the viscous stress. This paper investigates radiative tides as an alternative mechanism for accretion in disks in mass-transfer binary systems. We consider the process in which accretion is driven by the out-of-phase response of the disk to the tidal field of the secondary is considered. It is found that accretion can occur if the disk can be heated by some means other than by accretion itself. No, solution is possible in which the disk is heated by the energy released by accretion alone, if the amplitude of the tidal perturbation is small. Radiative tides may be important if the disk nearly fills the Roche lobe, so that tides are nonlinear at the disk edge. Another accretion process is considered in whch accretion is caused by an acoustic wave generated by the impact of the accretion stream upon the disk edge. This process is found to have limitations similar to those of radiative tidal accretion, and it is shown that impact-driven accretion is probably not important.Accretion requires three tasks to be performed. First, a local torque must be provided at each radius so that material at that radius can move inward. Second, a net amount of angular momentum must be removed from the disk, and not merely transferred from one radius to another. Third, the mechanical energy released as a result of accretion must be dissipated into heat and radiated away. Unfortunately, no single mechanism proposed so far in the literature, including those considered in this paper, succeeds in accomplishing all three of these tasks, without introducing ad hoc elements into the theory