Orbital evolution in binary and triple stars, with an application to SS Lacertae

We present equations governing the way in which both the orbit and the intr insic spins of stars in a close binary should evolve subject to a number of perturbing forces, including the effect of a third body in a possibly incl ined wider orbit. We illustrate the solutions in some binary star and tripl e star situations: tidal friction in a wide but eccentric orbit of a radio pulsar about a B star (0045-7319), the Darwin and eccentricity instabilitie s in a more massive but shorter period massive X-ray binary, and the intera ction of tidal friction with Kozai cycles in a triple star, such as beta Pe r at an early stage in that star's life, when all three components were zer o-age main sequence stars. We also attempt to model in some detail the inte resting triple system SS Lac, which stopped eclipsing in about 1950. We fin d that our model of SS Lac is quite constrained by the relatively good obse rvational data of this system and leads to a specific inclination (29 degre es) of the outer orbit relative to the inner orbit at epoch zero (1912). We make some predictions about changes to system parameters in the short term (20-40 yr) and also in the medium term (up to similar to 3000 yr). Althoug h the intrinsic spins of the stars have little effect on the orbit, the con verse is not true: the spin axes can vary their orientation relative to the close binary by up to 120 degrees on a timescale of about a century.