Global Disk Oscillations in Binary Be Stars

Abstract

Abstract We consider the effects of the tidal interaction with the companion, via orbital separation and the binary mass ratio, on the global one-armed oscillation modes in disks around binary Be stars. Our model takes into account a three-dimensional effect that contributes to mode confinement, which was recently found by Ogilvie (2008). We find that the one-armed oscillations are well confined in systems with disks larger than a few tens of stellar radii. In such systems, the oscillation period depends little on the binary parameters. On the other hand, in systems with smaller disks, where mode confinement is incomplete, the oscillation period increases with increasing orbital separation and/or decreasing binary mass ratio. The eigenmode is insensitive to the spectral type of the central star. Our results suggest that the dependence of the V$/$R oscillation period on the orbital separation and binary mass ratio should be observed only in short-period binary systems, and that, for systems with a similar orbital period, those with higher mass ratios will show shorter V$/$R variations.