Outmoving clumps in the wind of the hot O supergiant ζ Puppis

We present time series of ultra-high S/N, high-resolution spectra of the He II 4686 Angstrom emission line in the O4I(n)f supergiant zeta Puppis, the brightest early-type O star in the sky. These reveal stochastic variable substructures in the line, which tend to move away from the line center with time. Similar scaled-up features are well established in the strong winds of Wolf-Rayet stars (the presumed descendants of O stars), where they are explained by outward-moving inhomogeneities (e.g., blobs, clumps, and shocks) in the winds. If all hot star winds are dumped like that of zeta Pup, as is plausible, then mass loss rates based on recombination-line intensities will have to be revised downward. Using a standard "beta" velocity law, we deduce a value of beta = 1.0-1.2 to account for the kinematics of these structures in the wind of zeta Pup. In addition to the small-scale stochastic variations, we also find a slow systematic variation of the mean central absorption reversal.