Diamagnetic accretion in intermediate polars – I. Blob orbits and spin evolution

Abstract

We present numerical confirmation of King's diamagnetic blob accretion model. Spin evolution of the white dwarf leads to the relation Pspin ~ 0.1Porb observed for some intermediate polars. Fixing this relation gives a rough estimate of the white dwarf field strength in the range 106 > B > 104 G, depending on the uncertain blob parameters. We show that mass transfer from the companion is likely to be unstable except near spin equilibrium of the white dwarf, so that deviation from equilibrium should be short-lived (≲ 105 yr). Stable mass transfer for intermediate polars in spin equilibrium is similar to the conservative case and requires q < 0.7, Porb < 5–6 h.