We numerically study the precessing disk model for superhump in the SU UMa subclass of cataclysmic variables, using a two dimensional SPH code speci cally designed for thin disk problems.Two disk simulations for a binary with mass ratio q = 3 17 (similar to OY Car) are performed, in order to investigate the Lubow (1991 a,b) tidal resonance instability mechanism. In the rst calculation, a disk evolves under steady mass transfer from L 1 . In the second simulation, mass is added in Keplerian orbit to the inner disk. The two disks follow similar evolutionary paths. However the L 1 stream-disk interaction is found to slow the disk's radial expansion and to circularise gas orbits.The initial eccentricity growth in our simulations is exponential at a rate slightly less than predicted by Lubow (1991a). We do not observe the clearing of material from the resonance region, via the disk's tidal response to the m = 2 component of the binary potential, described in Lubow (1992). Instead the m = 2 response weakens as the disk eccentricity increases.Both disks reach an eccentric equilibrium state in which they undergo prograde precession. The rate of viscous energy dissipation in the disks has a periodic excess with a period matching the disks' rotation. The source is a large region in the outer disk. The mechanism by which the excess is produced is identi ed. The time taken for the periodic excess to develop is consistent with the rst appearance of superhumps in a superoutburst.

The computation of theoretical pulsar populations has been a major component of pulsar studies since the 1970s. However, the majority of pulsar population synthesis has only regarded isolated pulsar evolution. Those that have examined pulsar evolution within binary systems tend to either treat binary evolution poorly or evolve the pulsar population in an ad hoc manner. Thus, no complete and direct comparison with observations of the pulsar population within the Galactic disc has been possible to date. Described here is the first component of what will be a complete synthetic pulsar population survey code. This component is used to evolve both isolated and binary pulsars. Synthetic observational surveys can then be performed on this population for a variety of radio telescopes. The final tool used for completing this work will be a code comprised of three components: stellar/binary evolution, Galactic kinematics and survey selection effects. Results provided here support the need for further (apparent) pulsar magnetic field decay during accretion, while they conversely suggest the need for a re-evaluation of the assumed typical millisecond pulsar formation process. Results also focus on reproducing the observed PṖ diagram for Galactic pulsars and how this precludes short time-scales for standard pulsar exponential magnetic field decay. Finally, comparisons of bulk pulsar population characteristics are made to observations displaying the predictive power of this code, while we also show that under standard binary evolutionary assumption binary pulsars may accrete much mass.

We numerically study the tidal instability of accretion discs in close binary systems using a two-dimensional SPH code. We find that the precession rate of tidally unstable, eccentric discs does not only depend upon the binary mass ratio q. Although the (prograde) disc precession rate increases with the strength of the tidal potential, it also increases with the shear viscosity. Increasing the disc temperature has a retrograde impact upon the precession rate. We find that motion relative to the binary potential results in superhump-like, periodic luminosity variations in the outer reaches of an eccentric disc. The nature and location of the luminosity modulation is a function of the shear viscosity, nu. Light curves most similar to observations are obtained for nu values appropriate for a dwarf nova in outburst. We investigate the thermal-tidal instability model for superoutburst. A dwarf nova outburst is simulated by instantaneously increasing nu, which causes a rapid radial expansion of the disc. Should the disc encounter the 3:1 eccentric inner Lindblad resonance and become tidally unstable, then tidal torques become much more efficient at removing angular momentum from the disc. The disc then shrinks and mass flux through the disc increases. The resulting increase in disc luminosity is found to be consistent with the excess luminosity of a superoutburst.Comment: 12 pages, 14 encapsulated postscipt figures, accepted by MNRA