A dynamical simulation of the debris disk around HD 141569A

We study the dynamical origin of the structures observed in the scattered-light images of the resolved debris disk around HD 141569A. The disk has two conspicuous spiral rings and two large-scale spiral arms. We explore the roles of radiation pressure from the central star, gas drag from the gas disk, and the tidal forces from two nearby stars in creating and maintaining these structures. The disk's color, scattering function, and infrared emission suggest that submicron-sized grains dominate the dust population observed in scattered light. CO observations indicate the presence of up to 60 M_⊕ of gas. The dust grains are subject to the competing effects of expulsive radiation pressure (β > 1, where β is the ratio of the radiation and gravitational forces) and retentive gas drag. We use a simple one-dimensional axisymmetric model to show that the presence of the gas helps confine the dust and that a broad ring of dust is produced if a central hole exists in the disk. This model also suggests that the disk is in a transient, excited dynamical state, as the observed dust creation rate applied over the age of the star is inconsistent with submillimeter mass measurements. We model in two dimensions the effects of a flyby encounter between the disk and a binary star in a prograde, parabolic, coplanar orbit. We track the spatial distribution of the disk's gas, planetesimals, and dust. We conclude that the surface density distribution reflects the planetesimal distribution for a wide range of parameters. Our most viable model features a disk with initial radius 400 AU, a gas mass of 50 M_⊕, and β= 4 and suggests that the system is being observed within 4000 yr of the flyby periastron. The model reproduces some features of HD 141569A's disk, such as a broad single ring and large spiral arms, but it does not reproduce the observed multiple spiral rings or disk asymmetries nor the observed clearing in the inner disk. For the latter, we consider the effect of a 5M_J planet in an eccentric orbit on the planetesimal distribution of HD 141569A.