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 |5.64 × 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 |-I Ω Ω = 6 × 10³³ I₅₀ erg s⁻¹|⁠, which exceeds the accretion luminosity of AE Aqr by a factor of ∼ 120. A significant fraction of |-I Ω Ω| may be converted to the acceleration of particles as in a pulsar, which may explain the observed radio synchrotron emission and the reported γ-ray emission. We also give evidence that the secondary lies above the main sequence since the secondary mass inferred from the main-sequence mass-radius relationship is too large.