Rapid spindown of fast-rotating white dwarfs in close binary systems as a result of magnetic field amplification

The rapid braking on the white dwarf in the close binary AE Aqr can be expl ained in terms of the pulsar mechanism provided the magnetic moment of the star mu greater than or similar to 1.4 x 10(34) G cm(3). Under this conditi on the magnetic held is strong enough to prevent accretion with the rate le ss than or similar to 10(-4.3) M. yr(-1) onto the white dwarf surface, so t he traditional accretion-driven spin up mechanism cannot be applied to this system without additional assumptions. A scenario in which the initial mag netic moment of the white dwarf was essentially weaker than its present val ue is explored. A weakly magnetized (similar to 10(4) G) white dwarf was sl owly spinning up by accretion of matter from its normal companion until its period P greater than or similar to P-cr similar or equal to 20 s. When th e period had decreased beyond P,, the white dwarf lost its angular momentum via the gravitational waves that caused strong differential rotation. The magnetic field inside the star was winding up on a time scale of a month up to similar to 10(8)-10(9) G. This field manifests itself at the surface du e to buoyant instability producing a surface field of 10(7)-10(8) G. As a r esult the white dwarf changed its initial accretor state to the presently o bserved ejector state, i.e. it is spinning down predominantly due to the ma gneto-dipole waves generation and particle acceleration.