Pulsation in Rapidly Rotating Stars

Abstract

The line-profile variables observed on the upper main sequence have been interpreted by some astronomers to be the manifestation of nonaxisymmetric oscillations. More specifically, most of these variables can be modelled by prograde or corotating equatorial waves. In the absence of rotation, these waves have surface velocity distributions which are given simply by spherical harmonics. Unfortunately, the corresponding velocity fields in the presence of rotation are much more difficult to calculate. In this paper, I will summarize what is known about the effect of rapid rotation on the normal mode eigenfunctions of main sequence stars. The principal conclusions are as follows: Low-order, axisymmetric modes couple very strongly to rotation and their velocity distributions are very much different from those of their zero-rotation counterparts. On the other hand, higher-order (shorter wavelength), nonaxisymmetric modes couple only weakly to rotation and, therefore, retain many of the spherical harmonic properties that they possess in the absence of rotation.