Rapidly oscillating Ap (roAp) stars are cool magnetic CP2 stars which vary with periods of a few minutes and amplitudes less than 0.01 mag and 1 km/s in light and velocity. Analysis of their p-mode eigenfrequency patterns and splittings gives information about evolutionary state, rotation rate, magnetic field geometry and internal field strength (see Kurtz 1990; Matthews 1991).
We present here an example of how roAp pulsations can be used to obtain an estimate of the temperature structure of an Ap atmosphere.
The pulsation amplitudes of roAp stars decline more rapidly with increasing wavelength than other known pulsators. Matthews et al. (1990) explained this by the wavelength dependence of limb darkening and its weighting effect on the integrated amplitude of an (l, m) = (1,0) mode.