Superhumps, Magnetic Fields and the Mass-ratio in AM Canum Venaticorum

Abstract

We show that the observed K-velocities and periodicities of AM CVn can be reconciled given a mass ratio of 0.22 and a secondary star with a modest magnetic field of surface strength of order 1 Tesla. We see that the new mass ratio implies that the secondary is most likely semi-degenerate. The effect of the field on the accretion disc structure is examined. The theory of precessing discs and resonant orbits is generalised to encompass higher order resonances than 3:2 and shown to retain consistency with the new mass ratio.

6 pages, 4 figures, to appear in Monthly Notices of the Royal Astronomical Society