Stability of accretion onto magnetic white dwarfs is investigated via perturbation analysis. We consider a cooling function with composite power laws, and the power-law indices are appropriate for bremsstrahlung and optically thick cyclotron cooling. We find that the presence of cyclotron cooling generally suppresses the instability, consistent with numerical simulations by other investigators.

Photometry of the short-period (P ∼0.285 d) low-mass (M1 ∼0.67, M2 ∼0.48 M⊙) W UMa-type eclipsing binary RW Dor, mainly involving a good series of observations in 1987–88, using standard B and V filters at the Auckland Observatory, is examined. Analysis via light curve fittings alone permits both transit (near main sequence) and occultation (W-type contact binary) solutions. Consideration of proximity or other effects on the relatively small number of measured radial velocities gives rise to a more detailed review of the alternatives, though the (W-type) configuration determined by Hilditch, Hill & Bell (1992) is still confirmed. Further implications of this configuration are examined, given an apparent general trend to period decrease (Δ P/P ∼6 × 10−11), and some light curve asymmetry. This is consistent with the initially low-mass companion, Case-B scenario of Budding (1984). The evidence does suggest irregularity of the period variation however, and further detailed surveillance, including more spectroscopy, is desirable.

Our photometric CCD observations of the short-period cataclysmic star AR UMa in 2008 during its low state revealed light variability with a bigger period (by around 10%) and considerably smaller amplitudes than the previous ones. The light curve had a single-wave shape, opposite to the previously observed low states which revealed doubled-humped shape.