Post-Newtonian diagnostics for initial data

Using a post-Newtonian diagnostic tool developed by Mora and Will, we examine numerically generated quasiequilibrium initial data sets used in numerical evolutions of black hole-black hole, neutron star-neutron star and neutron star-black hole binary systems. The post-Newtonian equations include the effects of tidal interactions, parametrized by the compactness of the neutron stars and by suitable values of ``apsidal'' constants, which measure the degree of distortion of stars subjected to tidal forces. We find that the post-Newtonian diagnostic agrees well with black hole-black hole and neutron star-neutron star initial data, except where tidal distortions are becoming extreme. In comparing the diagnostic with preliminary numerical data on neutron star-black hole binaries, we find less agreement. We show that the differences could be interpreted as representing small residual eccentricity in the initial orbits.