THEORY FOR THE DISTORTED DIPOLE MODES OF THE RAPIDLY OSCILLATING AP STARS - A REFINEMENT OF THE OBLIQUE PULSATOR MODEL

Recently, one of the rapidly oscillating Ap stars, HR 3831, has been f ound to have an equally split frequency septuplet, though its oscillat ion seems to be essentially an axisymmetric dipole mode with respect t o the magnetic axis, which is oblique to the rotation axis (Kurtz 1992 , Monthly Notices Roy. Astron. Soc., 259, 701; Kurtz et al. 1993, Mont hly Notices Roy. Astron. Soc., 260, 343). In order to explain this fin e structure, we consider the magnetic stars by taking account of the p erturbations due to the magnetic fields and the rotation. We show that the effect of the magnetic field on the axisymmetric dipole modes dis torts the dipole oscillation pattern to have axisymmetric octupole com ponents, so that the frequency pattern becomes a septuplet rather than a triplet, and that the additional effect of the rotation causes the frequency pattern to be asymmetric. The formula allow us to obtain inf ormation concerning the magnetic fields, rotation, and geometrical con figuration of the star from the oscillation data.