3D modeling of accretion disks in close binaries: the precessional spiral density wave

Abstract

Three-dimensional numerical simulations of gas dynamics are used to study the flow pattern in a close binary system after it has reached the steady-state accretion regime. It is shown that an additional spiral density wave can exist in the inner parts of the cold accretion disk, where gas-dynamical perturbations are negligible. This spiral wave is due to the retrograde precession of the flowlines in the binary system. It is found that shape and position of a substantial part of the disk are specified by a precessional density wave. On timescales comparable to the orbital period, the precessional wave (and hence an appreciable fraction of the disk) will be virtually stationary in the observer’s frame, whereas the positions of other elements of the flow will vary due to the orbital rotation. The periodic variations of the positions of the disk and the bow shock formed when the inner parts of the circumbinary envelope flow around the disk result in variations of both the rate of angular-momentum transfer to the disk and the flow structure near the Lagrange point L 3 . All these factors lead to a periodic increase of the matter flow into the outer layers of the circumbinary envelope through the vicinity of L 3 .