The discovery of a brake on the white dwarf in AE Aquarii

Abstract

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 |$5.64 \times 10^{-14} \text s \enspace \text s^{-1}$| 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_ \text {wd} \enspace \text {sin}\enspace i = 2.04\enspace \text s $|⁠, yields a white dwarf mass of between 0.9 and 1.0 M⊙. The spindown power of the white dwarf is |$-I \Omega \dot \Omega = 6 \times 10^{33} \enspace I_{50} \enspace \text {erg} \enspace \text s^{-1}$|⁠, which exceeds the accretion luminosity of AE Aqr by a factor of ∼ 120. A significant fraction of |$-I \Omega \dot \Omega$| 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.