Accretion Belt Characteristics in a Hydrodynamic Evolution of a Contact Binary

Abstract

Abstract We compare features from the circulation model developed in Stȩpień for contact binaries to a long-term hydrodynamical evolution of a symmetric contact binary. The numerical evolution is fully three-dimensional and begins from an equilibrium structure in contact at one grid cell. As the evolution is conducted with Flow-ER, an explicit hydrodynamics code for self-gravitating fluids, we are not able to address energy transport or evolution on a thermal timescale. However, we are able to investigate the width and height of the equatorial accretion belt and the flow of material in and out of the inner Lagrange point. The flow of material between the two components arises quickly in the evolution and does not change significantly through tens of orbital periods. As the stellar components are modeled as polytropes of index 3/2 a slight numerical mass imbalance causes one component to only gain mass over the course of the simulation leading eventually to a dynamical merger of the contact binary.