ON THE RATE OF ORBITAL ANGULAR-MOMENTUM LOSS OF SYNCHRONOUSLY ROTATING MAGNETIC CATACLYSMIC VARIABLES

We present calculations of the efficiency of magnetic braking in synch ronously rotating magnetic binary systems, following the formulation o f Li, Wu and Wickramasinghe. We show that, for the observed range of m agnetic field strengths typical of AM Herculis binaries, the braking e fficiency has been overestimated by a large factor in current models. Our calculations also show that the orbital evolution of the high-fiel d AM Herculis binaries is driven by the loss of orbital angular moment um due to gravitational radiation rather than magnetic braking, if the se are the only two competing mechanisms.