Multiperiodicity of ζ Ophiuchi from Multisite Observations

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Abstract
We present results from simultaneous multisite high-resolution spectroscopic and photometric observations of ζ Oph (HD 149757) taken in 1993 May. Our spectroscopic data include about 100 hr of continuous monitoring of the star. The line-profile variations of He I λ6678, which are characterized by features traveling from blue to red, are well reproduced by two large-amplitude sinusoids and other sinusoids with smaller amplitudes. The period of the sinusoid with the largest amplitude is 2.018 hr (f1), which differs from the 2.43 hr of previous publications, although it is possible that 2.43 hr is an alias of 2.018 hr. The period of the second largest amplitude is, in agreement with previous studies, 3.337 hr (f2). Periods of smaller amplitude sinusoids are 2.432 hr (f3), 1.257 hr (f1 + f2), 1.008 hr (2f1), 2.107 hr (f4), 1.293 hr (f2 + f4), and 1.668 hr (2f2), all of which have some relation to the two main periods. The two principal periods have close superperiods of about 10.05 hr. We discuss the commensurability and other features of the periodicity. Our photometric observations, although limited, confirm again the very small amplitude of the light variations that are close to their detection limit. No counterpart of the 2.018 hr and 3.337 hr periods can be detected.