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Astron. Astrophys. 347, 915-918 (1999)

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

Nazar R. Ikhsanov

Central Astronomical Observatory of the Russian Academy of Science at Pulkovo, Pulkovo 65-1, 196140 Saint-Petersburg, Russia (ikhsanov@gao.spb.ru)

Received 15 March 1999 / Accepted 21 May 1999

Abstract

The rapid braking on the white dwarf in the close binary AE Aqr can be explained in terms of the pulsar mechanism provided the magnetic moment of the star [FORMULA]. Under this condition the magnetic field is strong enough to prevent accretion with the rate [FORMULA] onto the white dwarf surface, so the traditional accretion-driven spin up mechanism cannot be applied to this system without additional assumptions. A scenario in which the initial magnetic moment of the white dwarf was essentially weaker than its present value is explored. A weakly magnetized ([FORMULA] G) white dwarf was slowly spinning up by accretion of matter from its normal companion until its period [FORMULA] s. When the period had decreased beyond [FORMULA] 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 [FORMULA] G. This field manifests itself at the surface due to buoyant instability producing a surface field of [FORMULA] G. As a result the white dwarf changed its initial accretor state to the presently observed ejector state, i.e. it is spinning down predominantly due to the magneto-dipole waves generation and particle acceleration.

Key words: stars: novae, cataclysmic variables – stars: magnetic fields – stars: pulsars: general – stars: individual: AE Aqr

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© European Southern Observatory (ESO) 1999

Online publication: June 6, 1999
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