Although the modes have been well studied there remain a few open
issues. In the black hole case, the Kerr-Newman spectrum is known
only in a restricted case [124], so the general case should be studied, probably by evolving
the perturbation equations. For non-rotating stars, there remain
certain technical questions, i.e. to find if there exist a class
of
w
-modes with even larger imaginary part or the existence of extra
interface modes. But for rotating stars, even slowly rotating
ones, there remains much work [192]. There should be estimates of the fluid and spacetime modes for
slowly rotating stars for various realistic equations of state,
and the results should be incorporated into the method suggested
in [19] for the estimates of the stellar parameters. There should be
work towards understanding the possible interaction of
r
-modes with
g
-modes [176,
93]. And finally the time dependent perturbation equations for
rotating stars should be evolved, because in this way we expect
to see most of the new features that rotation induces in the
spectra (splitting, instabilities etc).