Magnetic field evolution in accreting white dwarfs

I discuss the evolution of the magnetic field of an accreting white dwarf. I show that the ohmic decay time is 7–12 billion years for the lowest order decay mode, almost independent of core temperature or mass. I then show that the magnetic field structure is substantially altered by accretion if the white dwarf mass increases at a rate> ˙ Mc ≈ (1–5) ×10 −10 M ⊙ yr −1. I discuss the implications of this result for observed systems, including the possible evolutionary link between AM Hers and intermediate polars. 1.