  We study the tidal effects of a Kerr black hole on a neutron star in black
hole-neutron star binary systems using a semi-analytical approach which
describes the neutron star as a deformable ellipsoid. Relativistic effects on
the neutron star self-gravity are taken into account by employing a scalar
potential resulting from relativistic stellar structure equations. We calculate
quasi-equilibrium sequences of black hole-neutron star binaries, and the
critical orbital separation at which the star is disrupted by the black hole
tidal field: the latter quantity is of particular interest because when it is
greater than the radius of the innermost stable circular orbit, a short
gamma-ray burst scenario may develop.
