INNER EDGE DRAG BY THE COMPACT STAR AND DISC STRUCTURE AND DYNAMICS IN CLOSE BINARY-SYSTEMS - 3D SPH NUMERICAL EXPERIMENTS

The aim of this work is to study the effect of the drag exerted by an asynchronous primary on accretion disc structure and dynamics in an in teracting close binary system. Comparison of two 3D SPH disc simulatio ns has been performed, the first relative to the customary synchronous case, the second to an asynchronous one, assuming the primary rotatio nal axis to be perpendicular to the orbital plane, and, in the latter case, the rotational angular velocity to be twice the orbital one, nam ely omega = 2 omega(0). Some tests have been carried out also in the c ases: omega = 1.5 omega(0), omega = 5 omega(0) and omega = 10 omega(0) , where omega is the primary angular velocity and omega(0) is the orbi tal angular velocity. The results relative to the omega = 2 omega(0) m odel show a hot accretion disc whose inner edge is characterized by an asymmetric rotational motion, an azimuthal compression wave and a rot ating local bump, which may explain luminosity variations observed in close binary systems. A hot wind coming from the outer edge of the dis c is also found. In this asynchronous model the accretion and ejection mass rates are lower and higher respectively, in comparison to those characteristic of the synchronous model. For faster rotation rates ome ga, the tests performed indicate that high ejection mass rates, both f rom the outer and inner edges, do not allow the development of a well defined accretion disc.