TIME-SERIES OBSERVATIONS OF O STARS .2. OPTICAL OBSERVATIONS OF ZETA-OPHIUCHI

We present photopolarimetry and extensive high-resolution, high-signal -to-noise optical spectroscopy of the rapidly rotating late O-type sta r zeta Ophiuchi (HD 149757). The polarimetric data show no substantial variability over 1 week (sigma(p) < 0.04%), while the spectroscopic d ata show characteristic line-profile variations in the form of ''bumps '' migrating from blue to red on typical time scales of several hours. These variations are relatively strong (amplitude approximately 1% of the continuum level) in He I lambda4471, and Si III lambdalambda4552, 4567, 4575. They are seen at lower amplitudes in Mg II lambda4481, bu t are almost undetectable (amplitude less than or similar to 0.3%) in He II lambdalambda4541, 4686 and N III lambdalambda4511, 4515, 4518. W e attribute this to a combination of equatorial gravity darkening and a latitudinally confined origin of the variations. Using a Fourier CLE AN technique, it is shown that the line-profile variations can be adeq uately represented as a set of sinusoids. The periods, combined with a n estimate of the rotational period, lead us to rule out rotational mo dulation as the origin of the variability. The phase changes of the si nusoids across the line-profiles indicate a repetitive pattern, consis tent with sectorial (l = -m) nonradial pulsation. We find four periods : P = 3.339 hr (Absolute value of m = 4), 2.435 hr (Absolute value of m = 5 or 6), 1.859 hr (Absolute value of m = 9 +/- 1), and either 1.36 6 or 1.292 hr (Absolute value of m = 11 +/- 1). The ''superperiods,'' P Absolute value of m, may be nearly commensurate (at approximately 13 -14 hr), but that commensurability is not exact.