Spiral and shock front development in accretion discs in close binaries: Physically viscous and non-viscous SPH modelling

INAF - Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123 Catania, Italy

Corresponding author: glanzafame@astrct.ct.astro.it

Received: 2 April 2002
Accepted: 5 November 2002

Abstract

A comparison between an accretion disc model, whose transport mechanisms are driven only by artificial viscosity, and a physically viscous accretion disc model for the same close binary system is performed here by adopting the same parameters and boundary conditions. These assumptions mean that artificial viscosity, included in both models, shares, together with physical viscosity, mass and angular momentum transport in the second disc model. The Smooth Particle Hydrodynamics (SPH) Lagrangian scheme has been adopted in both models and has been considered as for the viscous model according to the well-known Shakura and Sunjaev formulation. Physical viscosity is represented by the viscous force contribution as a divergence of the symmetric viscous stress tensor in the Navier-Stokes equation, whilst the viscous energy contribution is given by a symmetric combination of the symmetric shear tensor times to the particle velocity. Adopting a supersonic particle inflowing at the inner lagrangian point L1, clear spiral strong shocks in the radial flux develop from the inviscid 3D model. Extended spirals and shock fronts are even more evident in the viscous accretion disc model, which is larger than the non-viscous one in the XY orbital plane. Characteristics of the two disc structures as well as observational consequences are discussed.