The Disc Accretion in Gravitational Field of a Rapidly Rotating Neutron Star with a Rotationally Induced Quadrupole Mass Distribution

We analyze the effect of the quadrupole component in the mass distribution of a rapidly rotating neutron star on energy release in the boundary layer on the surface of the accreting star and in the accretion disk in the cases where the stellar radius is smaller (or larger) than the radius of the marginally stable circular orbit. We calculate the velocities and trajectories of the particles that fall on the stellar surface from the marginally stable orbit for a low- luminosity accreting source. The corresponding external gravitational field of the star is modeled by a new exact solution of the Einstein equations in vacuum. The parameters of this solution are adjusted by reconciling the numerical data for the radius of the marginally stable orbit and the gravitational redshift of Cook et al. (1994) with the corresponding data in the analytical solution. For various equations of state, we consider 1.4 solar mass normal sequences and maximum mass normal sequences.