A 3-D SPH model of helium accretion disks in the interacting binary white dwarf systems AM CVn and EC 15330-1403.
WOOD M.A. and SIMPSON J.C.
Abstract (from CDS):
We present the results of a numerical study of the dynamics of the helium accretion disks in the interacting binary white dwarf systems AM CVn and EC 15330-1403. These systems are apparently in continuous high state, suggesting high mass transfer rates and an approximately steady state disk structure. Our results are consistent with this model in that we find that, if a large artificial viscosity is used, the simulation develops spiral shocks which are quasi-stationary in the corotating frame of reference. These m = 2 spiral patterns should give rise to photometric variations with P1/2Porb, long inferred for AM CVn. Considerable departures from the average shock structure are seen on a timescale of a few orbits, but our results suggest that the point symmetry and phase of the shocks are maintained in the long term. The former is consistent with Fourier spectra which are variable for data runs of only a few hours in length, while the latter is consistent with long term stability of the light curve and absence of the fundamental frequency as found in WET observations. It has been suggested that a permanent superhump phenomenon explains the 20.77 µHz splitting observed in the time series photometry and the corresponding 13.38 h spectroscopic line-profile variations. We discuss our results within the context of this model.