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There is abundant evidence that essentially all luminous hot-star
winds contain time-dependent and anisotropic structures. IAU
Colloquium 169 was convened to review the observations of
variability and asphericity, to discuss the physical processes that
might cause such behavior and to look for evolutionary
consequences. The topics included OBA stars, Be stars, Wolf-Rayet
stars, Be stars, and luminous blue variables (LBVs). The role
played by rotation in shaping the stellar wind was a recurrent
theme. Photospheric pulsations and/or magnetic fields are
particularly appealing mechanisms for triggering the formation of
recurrent wind structures.
It is well known that stellar winds are variable, and the
fluctuations are often cyclical in nature. This property seems to
be shared by the winds of cool and hot stars, even though their
outflows are driven by fundamentally different physical mechanisms.
Since very similar models have been proposed to explain the
cyclical wind variations observed in a wide variety of stars, the
time was ripe for astrophysicists from many different
sub-disciplines to present the state of the art in a concise form.
The proceedings will provide a useful, up-to-date overview of the
observations, interpretation, and modelling of the time-dependent
mass outflows from all sorts of stars.
This specialized workshop was conceived during the workshop on "Non
isotropic and Variable Outflows from Stars", which was held at the
Space Telescope Science Institute in October, 1991. At that
meeting, the four of us collectively decided that the time was ripe
for an even more focussed discussion of the basic issues in the
area of hot-star wind instability and its observable
manifestations. Not that the big problems have been solved! Rather,
we are currently in a phase of rapid development, both with regard
to the models and to the observations. The key issue at this new
workshop would be to decide how the time-dependent structures
observed in hot-star winds (e. g. , NACs, DACs, blobs, clumps,
filaments, shells, puffs, jets, etc. ) relate to radiative and
other instabilities. Further questions concern the role of
turbulence and the nature of its driver, and the effect of stellar
rotation, pulsation, and magnetic fields on time-dependent
phenomena in hot-star winds. Of no less importance is the impact of
stellar wind variability on the derivation of mass-loss rates, on
stellar evolution, and on momentum/energy deposition in the
interstellar medium. To attain our goal of maximum confrontation
(in the positive sense!) we decided: (1) to limit the workshop to
the observers and theoreticians most active in this field in the
world; (2) to insist that virtually all participants present a
talk, thereby avoiding the distraction of poster sessions; and (3)
to allocate approximately half of the allotted time to discussion.
It is well known that stellar winds are variable, and the
fluctuations are often cyclical in nature. This property seems to
be shared by the winds of cool and hot stars, even though their
outflows are driven by fundamentally different physical mechanisms.
Since very similar models have been proposed to explain the
cyclical wind variations observed in a wide variety of stars, the
time was ripe for astrophysicists from many different
sub-disciplines to present the state of the art in a concise form.
The proceedings will provide a useful, up-to-date overview of the
observations, interpretation, and modelling of the time-dependent
mass outflows from all sorts of stars.
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