Non-radial oscillations

The problem of the adiabatic nonradial oscillations of spherical stars is reviewed and results recalled for a variety of models. The anomalous behavior of the eigenfunctions for highly condensed models is related to the apparent mobile singularities depending on the eigenvalues. Tables of Q-values are provided to facilitate possible applications to variable stars. In the case of the gravity modes, the existence of multiple spectra, some stable (g/plus/ modes) and some unstable (g/-/ modes) if superadiabatic and subadiabatic regions alternate, is discussed. As far as vibrational stability is concerned, a general expression is given for the 'damping coefficient'. Attention is drawn to the possibility for g(plus) modes of becoming vibrationally unstable under the effect of various factors and in various models, including the sun where this was advocated as a possibility of relieving the neutrinos difficulty. Finally, the present status of the most obvious candidates among variable stars for nonradial oscillations, the beta Canis Majoris stars and the rapid blue variables (white dwarfs) is briefly reviewed.