Tilt, Warp, and Simultaneous Precessions in Disks

Warps are suspected in disks around massive compact objects. However, the pro-posed warping source – non-axisymmetric radiation pressure – does not apply to white dwarfs. In this letter we report the first Smoothed Particle Hydrodynamic simulations of accretion disks in SU UMa-type systems that naturally tilt, warp, and simultaneously precess in the prograde and retrograde directions using white dwarf V344 Lyrae in the Kepler field as our model. After ∼79 days in V344 Lyrae, the disk angular momentum Ld becomes misaligned to the orbital angular momentum Lo. As the gas stream re-mains normal to Lo, hydrodynamics (e.g., the lift force) is a likely source to disk tilt. In addition to tilt, the outer disk annuli cyclically change shape from circular to highly eccentric due to tidal torques by the secondary star. The effect of simultaneous pro-grade and retrograde precession is a warp of the colder, denser midplane as seen along the disk rim. The simulated rate of apsidal advance to nodal regression per orbit nearly matches the observed ratio in V344 Lyrae