Non-radial oscillations of the rapidly rotating Be star HD 163868

Abstract

We study the pulsational stability of the rapidly rotating Be star HD 163868 using a newly developed 2D oscillation code which takes the Coriolis force fully into account and compare our results with observations (MOST) and recent other stability analyses of this ~ 6 Msun star. We find both prograde and retrograde overstable modes (although more prograde than retrograde modes) and confirm the existence of low degree odd r-modes destabilised by the kappa-mechanism. The ultra-low frequency modes that could not be explained in a previous analysis are interpreted as high degree, retrograde m=1 modes. A reasonably good fit to the observed oscillation spectrum is possible if we assume that only even modes are observed. This requires a nearly equator-on view of the observed star, consistent with the measured high v sin i value of 250 km/s.