  We study equilibrium sequences of close binary systems composed of identical
polytropic stars in Newtonian gravity. The solving method is a multi-domain
spectral method which we have recently developed. An improvement is introduced
here for accurate computations of binary systems with stiff equation of state
($\gamma > 2$). The computations are performed for both cases of synchronized
and irrotational binary systems with adiabatic indices $\gamma=3,~2.5,~2.25,~2$
and 1.8. It is found that the turning points of total energy along a
constant-mass sequence appear only for $\gamma \ge 1.8$ for synchronized binary
systems and $\gamma \ge 2.3$ 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.
