THE DISCOVERY OF A BRAKE ON THE WHITE-DWARF IN AE AQUARII

We report the discovery of a rapid spindown of the 33-s rotation period of the white dwarf in AE Aqr at a steady rate of 5.64 x 10(-14) s s-1 over a baseline of at least 14.5 yr. The newly derived orbital period by Welsh, Horne & Gomer is confirmed, and it is shown that the secondary star's absorption-line radial velocities provide the correct phasing for the 33-s oscillations if they originate at the white dwarf. The amplitude of the pulse-timing delays, a(wd) Sin i = 2.04 s, yields a white dwarf mass of between 0.9 and 1.0 M.. The spindown power of the white dwarf is - IOMEGAOMEGA = 6 x 10(33) I50 erg s-1, which exceeds the accretion luminosity of AE Aqr by a factor of approximately 120. A significant fraction of - IOMEGAOMEGA may be converted to the acceleration of particles as in a pulsar, which may explain the observed radio synchrotron emission and the reported gamma-ray emission. We also give evidence that the secondary hes above the main sequence since the secondary mass inferred from the mainsequence mass-radius relationship is too large.