We study stationary axisymmetric configurations of a star model consisting of
two barotropic fluids, which are uniformly rotating at two different rotation
rates. Analytic approximate solutions in the limit of slow rotation are
obtained with the classical method of Chandrasekhar, which consists of an
expansion of the solution in terms of the rotation rate, and which is
generalized to the case of two fluids in order to apply it to the present
problem. This work has a direct application to neutron star models, in which
the neutron superfluid can rotate at a different speed than the fluid of
charged components. Two cases are considered, the case of two non-interacting
fluids, and the case of an interaction of a special type, corresponding to the
vortices of the neutron superfluid being completely pinned to the second fluid.
The special case of the equation of state P~rho^2 is solved explicitly as an
illustration of the foregoing results.Comment: 9 pages, uses aa.sty and amssymb.sty; submitted to Astron.Astrophy
