Vol. 579
In section 7. Stellar structure and evolution

Quasi-periodic oscillations in accreting magnetic white dwarfs I. Observational constraints in X-rays and optical

by J.M. Bonnet-Bidaud, M. Mouchet, C. Busschaert, et al. A&A 579, A24

Quasi-periodic oscillations in accreting magnetic white dwarfs. II. The asset of numerical modelling to interpret observations

by C. Busschaert, E. Falize, C. Michaut, et al. A&A 579, A25


The bursting and quasi-period pulsations on timescales of a few seconds that are observed in magnetized accreting white dwarfs have presented a theoretical challenge for decades. The mass accumulates at the magnetic poles, channeled by the strong stellar field into a shock near the surface. This pair of papers reports computation of the flow and self-consistently includes detailed hydrodynamic heating and cooling by thermal bremsstrahlung and cyclotron emission using the HADES radiation-hydrodynamics code. The most significant advance is the production of real XR and optical flux light curves -- the two bands are related -- along with the power spectra of the oscillations. The models predict a dependence of the QPO frequencies on the field strength and predict that, for a broad range of accretion states, there is a critical magnetic field strength above which the oscillations are damped.