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Title:
Time-Series Observations of O Stars. II. Optical Observations of zeta Ophiuchi
Authors:
Reid, A. H. N.; Bolton, C. T.; Crowe, R. A.; Fieldus, M. S.; Fullerton, A. W.; Gies, D. R.; Howarth, I. D.; McDavid, D.; Prinja, R. K.; Smith, K. C.
Publication:
Astrophysical Journal v.417, p.320 (ApJ Homepage)
Publication Date:
11/1993
Origin:
APJ; KNUDSEN
ApJ Keywords:
LINE: PROFILES, STARS: EARLY-TYPE, STARS: INDIVIDUAL CONSTELLATION NAME: ZETA OPHIUCHI, STARS: OSCILLATIONS
DOI:
10.1086/173315
Bibliographic Code:
1993ApJ...417..320R

Abstract

We present photopolarimetry and extensive high-resolution, high-signal-to-noise optical spectroscopy of the rapidly rotating late O-type star Ζ Ophiuchi (HD 149757). The polarimetric data show no substantial variability over 1 week (σp < 0.04%), while the spectroscopic data 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 ˜1% of the continuum level) in He I λ4471, and Si III λλ4552, 4567, 4575. They are seen at lower amplitudes in Mg II λ4481, but are almost undetectable (amplitude ≲0.3%) in He II λλ4541, 4686 and N III λλ4511, 4515, 4518. We attribute this to a combination of equatorial gravity darkening and a latitudinally confined origin of the variations.

Using a Fourier CLEAN technique, it is shown that the line-profile variations can be adequately represented as a set of sinusoids. The periods, combined with an estimate of the rotational period, lead us to rule out rotational modulation as the origin of the variability. The phase changes of the sinusoids across the line-profiles indicate a repetitive pattern, consistent with sectorial (1 = -m) nonradial pulsation. We find four periods: P = 3.339 hr (|m| = 4), 2.435 hr (|m| = 5 or 6), 1.859 hr (|m| = 9±1), and either 1.366 or 1.292 hr (|m| = 11±1). The "superperiods," P|m|, may be nearly commensurate (at ˜13-14 hr), but that commensurability is not exact.

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