The origin of soft X-ray pulsations in dwarf novae at outburst and the DQ Herculis phenomenon

A recent study of X-ray emission from non-magnetic cataclysmic variables¹ concludes that most of the hard (≳2 keV) flux is produced in a corona formed by the accreting material around the white dwarf. EXOSAT observations of SS Cygni (see accompanying paper)² strongly support this model, confirming several of its detailed predictions. The model suggests that soft (≲2 keV) X-ray production is controlled largely by transport processes into the white-dwarf body which remove most of the energy from the accreting matter. I point out here that, because even weak magnetic fields can exert a marked influence on transport processes, tbere is a natural explanation for the quasi-periodic oscillations seen in soft X-ray observations of dwarf novae at outburst^3-5. I suggest further that the puzzling behaviour of the `DQ Herculis' system (DQ Her, V533 Her and AE Aqr) may be explained in this light.