transparent and in many cases analytical results can be obtained which shed light on the underlying physics.

The tensor virial method is not the only tool for investigating the properties of ellipsoidal figures. Alternative formulations exist in the literature and we refer to Refs. [@CARTER; @IPSER; @LRS] for further details; for a pedagogical introduction see the textbook [@ST]. Note, also, that various formulations of the theory of ellipsoids, to a large extent, are equivalent.

Superfluid oscillations were studied using various methods and approximations in the past decade. Epstein pointed out that the superfluidity of neutron star interiors has potentially important effects on the propagation of seismically excited acoustic waves. It allows for additional types of waves to propagate by virtue of doubling of degrees of freedom in a superfluid; superfluid phases create acoustic discontinuities in which wave velocities or polarizations change abruptly on the bounding interfaces [@EPSTEIN]. The effects of superfluidity on global hydrodynamic oscillations were investigated by Lindblom and Mendell [@LINDBLOM1] in a model where the superfluid and the normal fluid are coupled via gravitational attraction and the [*entrainment effect*]{}[^1]. Their solutions reveal that the lowest frequency pulsations are almost indistinguishable from those derived from the ordinary-fluid hydrodynamics; however, 