Opacity enhancements in the stellar wind of 68 Cygni - not "shells" or "puffs".

Abstract

Results presented from a study of variability in the stellar wind of 68 Cyg [O7.5 III((f))], based on 33 IUE high-resolution spectra taken over ≡7 days in 1986 August. Significant changes are evident in the Si IV resonance line profiles on time-scales as short as ≡1 hr; these changes are characterized by broad low-velocity (≡0.55v) absorption enhancements which evolve into high-velocity (≥0.8v) narrow absorption components over a period of ≡1 day. The recurrence time-scale for the appearance of the broad features is ≡15 - 20 hr. Three well monitored consecutive sequences of progressive opacity enhancement are studied in detail. The authors conclude that the discrete absorption variability in 68 Cyg is not due to 'shells' or 'puffs' of matter, but instead arises from material passing through perturbations in the flow, which may be illustrated in terms of spirally wound-up streams. These perturbations have much in common with Mullan's proposed corotating interaction regions (CIRs).