OPTICAL TIME-SERIES SPECTROSCOPY OF THE O4 SUPERGIANT ZETA-PUPPIS

We present time-resolved echelle spectroscopy of the 04I(n)f supergian t zeta Puppis. Variations are observed in all absorption-line profiles , with typical peak-to-peak amplitudes of similar to 2% of the continu um intensity (similar to 4% in He II lambda 5411 Angstrom). All observ ed absorption lines (He I, He II, N IV, and C IV) show the same gross characteristics, with 'bumps' and 'dips' moving blue-to-red through th e profiles, with no detectable line-to-line velocity shifts in the var iability pattern (< 15 km s(-1)) although there are differences in the relative amplitudes across the lines. The time dependence of the vari ability is investigated by using a 2-D CLEAN power-spectrum analysis. Significant power is found at a period of similar to 8.54 hr; the unde rlying signal is marginally consistent with sectorial, prograde non-ra dial pulsations with l = -m = 2, although this does not account for al l the observed variability. The blue emission wing of H alpha was incl uded in the echellograms, and, in contrast to the absorption lines, sh ows features moving red-to-blue with a period of 8.5 hr (the absorptio n-line period). The H alpha data also show features at a period of 19. 6 hr (the recurrence time of the 'discrete absorption features' observ ed in UV P-Cygni resonance lines), moving blue-to-red at velocities mo re positive than -280 km s(-1) and red-to-blue at more negative veloci ties. The temporal behaviour of H alpha provides the first direct evid ence for a dynamical response of a radiation-driven wind to basal velo city fields.