Photometric amplitudes and phases of nonradial oscillation in rotating stars

Effects of rotational mode coupling on photometric parameters of stellar oscillations are studied. At moderate rotation rates, a strong coupling between modes of spherical harmonic degree, , differing by 2 and of the same azimuthal order, m, takes place if the frequencies are close. This is a common situation amongst main sequence pulsators. Numerical results for a sequence of β Cephei star models are reported for the two- and three-mode couplings. One consequence of mode coupling is that modes of higher degree should be considered in photometric mode identification. Modes with nominal degree acquire substantial components and therefore are more likely to reach detectable amplitudes. Coupled mode positions in the amplitude ratio – phase difference diagrams, based on multicolour photometry, become both aspect- and m-dependent. Examples of the mode path in the diagram with varying aspect are given. The diagrams remain a useful tool for mode identification in rotating stars but the tool must be used with care.