Magnetic spin-orbit coupling and mass transfer rates in the polars

The magnetic torques resulting from an asynchronous white dwarf in an AM He rculis binary are considered. The magnetic field induced in the secondary l eads to an orbital torque which affects the evolution rate of its Roche lob e, An over-synchronous primary transfers angular momentum to the orbit whic h significantly reduces the rate of shrinkage of the lobe, for a range of a synchronous periods. Although the effect on the total evolution time of the binary is small, the temporarily reduced accretion rate has important cons equences for the condition to approach synchronism.