Slowly rotating two-fluid neutron star model

We study stationary axisymmetric configurations of a star model consisting of two barotropic fluids, which are uni- formly rotating at two different rotation rates. Analytic approx- imate solutions in the limit of slow rotation are obtained with the classical method of Chandrasekhar, which consists of an ex- pansion 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 dif- ferent 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 vor- tices of the neutron superfluid being completely pinned to the second fluid. The special case of the equation of state P / 2 is solved explicitly as an illustration of the foregoing results.