Amplitude variability in satellite photometry of the non-radially pulsating O9.5V star ζ Oph

We report a time series analysis of satellite photometry of the non-radially pulsating Oe star ζ Oph, principally using data from the Solar Mass Ejection Imager obtained during 2003–2008, but augmented with Microvariability and Oscillations of STars and Wide-field InfraRed Explorer results. Amplitudes of the strongest photometric signals, at 5.18, 2.96 and 2.67 d−1, each vary independently over the 512-year monitoring period (from ∼50 to ≲2 mmag at 5.18 d−1), on time-scales of hundreds of days. Signals at 7.19 and 5.18 d−1 have persisted (or recurred) for at least two decades. Supplementary spectroscopic observations show an Hα emission episode in 2006; this coincided with small increases in amplitudes of the three strongest photometric signals.