Type-N,shear-free,perfect-fluid spacetimes with a barotropic equation of state

We present the class of Petrov-typeN, shear-free, perfect-fluid solutions of Einstein's field equations in which the fluid satisfies a barotropic equation of statep=p(w) andw+p0. All solutions are stationary and possess a three- parameter, abelian group of local isometries which act simply transitively on timelike hypersurfaces. Furthermore, there exists one Killing vector parallel to the vorticity vector and another parallel to the four-velocity. This class of solutions is identified as part of a larger class present in the literature.