RELATIVISTIC FORMALISM TO COMPUTE QUASI-EQUILIBRIUM CONFIGURATIONS OFNONSYNCHRONIZED NEUTRON-STAR BINARIES

A general relativistic version of the Euler equation for perfect fluid hydrodynamics is applied to a system of two neutron stars orbiting ea ch other. In the quasiequilibrium phase of the evolution of this syste m, a first integral of motion can be derived for certain velocity fiel ds of the neutron star fluid including the (academic) case of corotati on with respect to the orbital motion (synchronized binaries) and the realistic case of counterrotation with respect to the orbital motion. The velocity field leading to this latter configuration can be compute d by solving three-dimensional vector and scalar Poisson equations. [S 0556-2821(97)05024-8].