Spiral Structures and Shocks in Accretion Discs in Close Binary Systems: the Role of the Injection Velocity at the Inner Lagrangian Point

In our previous paper (Lanzafame et al. 2000, PASJ 52, 515) we showed, through 2D SPH simulations, that the stellar mass ratio, $ M_{2}/M_{1}$, of a close binary system (that determines the $ L_{1}$ position and then the initial specific angular momentum at $ L_{1}$) plays a fundamental role in the formation and development of spiral structures and shock fronts in the radial flow of accretion discs. In that work only a quasi-sonic value of the injection velocity at $ L_{1}$ was considered. In the present work we also carried out 2D SPH simulations with the aim to investigate the development of such structures, while keeping constant the mass of the compact primary ($ M_{1} = 1 M_\odot$) and the separation between the two components, and assuming as an initial condition of two different supersonic injection velocities at $ L_{1}$, characterizing two sets of simulations. For each set we considered four values of the secondary to primary mass ratio, $ M_{2}/M_{1}$. We worked out 2D models because the damping effect of the artificial viscosity is too strong in 3D. Furthermore, the 2D environment seems to be the most suitable in order to be evidence of shock fronts in highly compressible gases. Our aim in these two works was to enhance the initial kinematic conditions (from sonic to strongly supersonic) to stress the idea that spiral structures and shock front development are influenced by the initial specific angular momentum at $ L_{1}$. The results show that these structures are more evident with the increasing injection velocity at $ L_{1}$ and the increasing $ L_{1}$ distance from the primary.