The role of physical viscosity in accretion discs in close binaries: high compressibility and low compressibility SPH modeling

Abstract

Simulations of 3D stationary accretion disc models for the same close binary system have been performed both in high and low compressibility regimes in the Smooth Particle Hydrodynamics (SPH). In all models artificial viscosity operates. The presence of physical viscosity characterizes the so called “physically viscous” or “viscid” models. A polytropic index γ = 5/3 has been adopted for the low compressibility disc models, whilst a γ = 1.01 has been adopted for high compressibility ones. Therefore, we investigated the role of physical viscosity in mass and angular momentum transport in viscid models and made a comparison with inviscid ones. A value of the parameter α = 1 has been considered for the physically viscous models, according to the well‐known Shakura and Sunjaev formulation. The results show that physical viscosity supports and favours accretion disc formation in the low compressibility case, but no spiral shocks develop. Spiral shocks in the radial flux develop in all high compressibility models. Physical viscosity efficiently supports mass, angular momentum and heat radial transport towards the compact primary star as well as radial disc spread.