Quasiequilibrium sequences of synchronized and irrotational binary neutron stars in general relativity. II. Newtonian limits

Abstract

We study equilibrium sequences of close binary systems composed of identical polytropic stars in Newtonian gravity. The solving method is a multidomain spectral method which we have recently developed. An improvement is introduced here for accurate computations of binary systems with a stiff equation of state $(\ensuremath{\gamma}>2).$ The computations are performed for both cases of synchronized and irrotational binary systems with adiabatic indices $\ensuremath{\gamma}=3, 2.5, 2.25, 2,$ and $1.8.$ It is found that the turning points of total energy along a constant-mass sequence appear only for $\ensuremath{\gamma}>~1.8$ for synchronized binary systems and $\ensuremath{\gamma}>~2.3$ for irrotational ones. In the synchronized case, the equilibrium sequences terminate by the contact between the two stars. On the other hand, for irrotational binaries, it is found that the sequences terminate at a mass shedding limit which corresponds to a detached configuration.