Inner Edge Drag by an Asynchronous Primary and Accretion Disc Structure in Close Binaries

Abstract

In this work a 3–D ‘Smoothed Particle Hydrodynamics’ ([1]; [4]; [5]) accretion disc is simulated where particles at its inner edge are dragged by a fast spinning compact central star, as in the case of the intermediate polars. The angular velocity of the central star is twice the orbital angular velocity ωo. This drag can be attributed mainly to viscous interaction in the dense compact star atmosphere, although magnetic coupling may also play a role.Our simulations have been performed for a system with a primary (a white dwarf) mass M1 = 1.3 M⊙, a secondary mass M2 = 2.2 M⊙, a separation between the components (centre to centre) d12 = 6.33 1011 cm and an orbital period = 1.7 d, the integration time being as long as ≃ 75 d. As in [2] and [3], we have considered quasi-polytropic structures with γ = 1.01. We adopt the term quasi-polytropic since we have in fact solved also an energy equation.