Pulsations of the Oe star ζ Ophiuchi from MOST satellite1 photometry and ground-based spectroscopy

Twenty-four days of highly precise Microvariability and Oscillations of Stars ( MOST) satellite photometry obtained in mid-2004 of the rapidly rotating O9.5 V star zeta Oph have yielded at least a dozen significant oscillation frequencies between 1 and 10 cycles day(-1), clearly indicating its relationship to beta Cephei variables. Eight periods were found in He I lambda 4922 and H beta line profile variations (LPV) of which six coincide with those from the MOST photometry. This unique photometric and spectroscopic detection of radial and nonradial pulsations leads to a plausible model in which high l-modes are excited when their frequencies in the corotating frame are similar to those of low-order radial modes. We propose that the dominant photometric 4.6 hr period (f(1)) corresponds to a radial first overtone excited by the k-mechanism associated with the Fe opacity bump. No unambiguous rotational period can be identified in either the light curve or the LPV.