Outmoving Clumps in the Wind of the Hot O Supergiant ζ Puppis

Abstract

We present time series of ultra-high S/N, high-resolution spectra of the He II 4686 A emission line in the O4I(n)f supergiant ζ 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 clumped like that of ζ Pup, as is plausible, then mass loss rates based on recombination-line intensities will have to be revised downward. Using a standard velocity law, we deduce a value of β = 1.0-1.2 to account for the kinematics of these structures in the wind of ζ Pup. In addition to the small-scale stochastic variations, we also find a slow systematic variation of the mean central absorption reversal.