Overstable magnetic convection and the rapidly oscillating Ap stars

Two analyses are presented of a mechanism recently suggested by Shibahashi to account for the oscillations of ''rapidly oscillating Ap stars''. This mechanims is based on overstable magnetic connection. A thin, superadiabatic zone in the outer parts of a star pervaded by only a moderately strong magnetic field can lead to overstable oscillations. The periods of these oscillations are expected to be of the order of the observed periods. Moreover, these oscillations should hae the magnetic axis as the pulsation axis. Growth times of these oscillations are short enough for to be interesting. One of these analyses is based on a ''blob'' model and is intended to be physically somewhat clear. The other is a local analysis and shows that the ''blob'' model is essentially in agreement with this analysis.