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Session 63 - The Frontiers of Far Ultraviolet Astrophysics - II.
Topical, Oral session, Wednesday, June 10
Sierra/Padre,
P Cygni profiles were first detected in the ultraviolet resonance lines of luminous OB stars during sounding rocket flights more than 30 years ago. Since then, there have been spectacular advances in our understanding of the mechanism responsible for driving hot-star winds (which is momentum transfer from the stellar radiation field to the wind material by scattering in line transitions) and the astrophysical consequences of the resultant mass loss (which include altering the evolutionary track of the star and depositing energy, momentum, and chemically enriched material into the interstellar medium). Although a wealth of spectroscopic information has been returned by UV and far-UV satellite observatories, and sophisticated model atmosphere programs have been developed to interpret these data, several fundamental challenges to our understanding still remain. These include: (a) accurate empirical determinations of mass-loss rates from the P Cygni profiles of resonance lines; (b) detailed knowledge of the processes that determine the ionization balance in the wind; and (c) the nature of the variability exhibited by hot-star winds. This review will emphasize the diagnostic leverage that can be applied to these problems by spectroscopic observations in the far-UV. The Far Ultraviolet Spectroscopic Explorer (FUSE) satellite will have greater spectral resolution and sensitivity and/or a longer operational lifetime than other FUV missions, and consequently rapid progress in solving these problems is expected. Thus, on the near horizon lies the tantalizing prospect of using hot-star winds as quantitative tools to probe young stellar populations in a variety of astronomical settings.
