Time-dependent accretion onto magnetic white dwarfs: Effects of cyclotron emission

TLDR: In this article, the effects of cyclotron cooling stabilize the flow if the magnetic field is large enough for a 0.5 M/sub sun/white dwarf accreting 1 g cm S s, the flow is stable if B is more than or approximately equal to 2 x 10X gauss.

Abstract: Previous accretion models have shown that if the cooling is due to optically thin bremsstrahlung, the flow is unstable. The shock height oscillates with a period approx.1 s, which corresponds to the cooling time for parameters characteristic of the AM Her binaries. Here we show that the effects of cyclotron cooling stabilize the flow if the magnetic field is large enough. For a 0.5 M/sub sun/ white dwarf accreting 1 g cm S s , the flow is stable if B is more than or approximately equal to 2 x 10X gauss. We also show that the bremsstrahlung X-ray emission and the optical cyclotron emission are 180 out of phase when oscillations are present. The relevance of these calculations to the observed optical oscillations, with periods of approx.1 s, in two AM Her stars is discussed.