Instability and Variability of Hot-Star Winds, 1994
Proceedings of an International Workshop Held at Isle-aux-Coudres, Quebec Province, Canada 23–27 August, 1993

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.

Overview Talks.- Theory Review: Line-Driven Instability and Other Causes of Structure and Variability in Hot-Star Winds.- Compressible Turbulence or Spatio-Temporal Chaos?.- Observational Aspects of Wind Variability.- Session 1: Spectroscopic Observations of Structures in Winds of Ob Stars.- Observations of Structure in the Stellar Wind of HD 152408.- Wind Variability in Intermediate Luminosity B Supergiants.- Monitoring the Winds of Hot Stars with HST/GHRS.- Winds of Magnetic B Stars.- Session 2: Connections between Photospheric and Wind Variability in Ob Stars.- Photospheric Variability of O Stars.- Wind Variability in O-Type Stars. On the Behaviour and Origin of DACs.- Session 3: Spectroscopic Observations of Structure in Winds of Wr-Stars.- Optical Spectroscopy of Inhomogeneities in the Winds of Wolf—Rayet Stars.- Erratum: The 2.27 Day Period of WR 134 (HD 191765).- Wolf—Rayet Stars as (Potentially) Fast Rotators with Rotationally-Induced Instability.- Further Results on the Line-Profile Variability of WR 134.- Optical Observations of Line Profile Variability in the WN5 Star HD 50896.- Simultaneous Optical and UV Observations of Variability in HD 50896.- Session 4: Constraints on Wind Structure from IR and Radio Observations.- IR- and Radio-Fluxes from Smooth and Clumped Wind Models of Wolf—Rayet Stars.- Clumped Structure of WR Winds Derived from IR Observations of WR + O Binaries: Some Constraints on the Light Curve Solution for V444 Cygni.- Analysis of Optical and IR Light Curves of the WR Binary V444 Cygni: Are Clumps Still Present?.- The Infrared and Radio Continuum of OB-Stars.- Nonthermal Radio Emission from Hot Star Winds. Its Origin and Physical Implications.- Session 5: X-Ray Observations of Stellar-Wind Structure.- ROSAT en EUVE Observations of BStars.- Constraints on Hot Star X-Ray Source Characteristics from Combined Analysis of X-Ray and UV Observations.- Particle Acceleration, X-Rays, and Gamma-Rays from Winds.- ROSAT X-Ray Light Curves of Early-Type Stars. A Search for X-Ray Time Variability of OB Stars.- ROSAT X-Ray Observations of the WR Stars HD 50896 (WN5) and ? Velorum (WC8 + O9I).- Session 6: Constraints on Wind Structure from Polarimetric Observations.- Spectropolarimetric Variability in OB Stars.- Spectropolarimetry of Hot, Luminous Stars.- Spectropolarimetric Modelling of Hot Star Wind Structure.- Spectropolarimetric Observations of WR 137.- Session 7: Phenomenological Models of Time-Dependent Wind Structure.- Wavelet Analysis of Wolf—Rayet Emission Line Variability. Evidence for Clumping.- Filaments, Disks, and Jets for OF and WR Stars.- Session 8: Hydrodynamic Simulations of the Evolution of Wind Structure.- Structure and Energy Transfer of Unstable Hot Star Winds.- Synthesis of Line Profiles from Models of Structured Winds.- X-Ray Emission in Wind Instability Simulations.- 1-D Models of Induced Density Enhancements in Hot-Star Winds.- Effects of Rotation on Hot Star Winds.- 2-D Hydrodynamical Simulations of Wind Compressed Disks (Abstract).- Growth of the Line-Profile Variation Region during BE Episodes in Lambda Eridani.- Session 9: Time-Dependent, Unstable Winds: Why Bother?.- Consequences of Clumping in Hot-Star Winds.- Round-Table Summary.- Closing Comments: Instability and Variability in Hot Star Winds.- Wind-Wind Collisions in WR + O and O + O Binaries.- Summary Comments.- Impressions of the Workshop.- Summary Comments.- General Discussion.- First Author Index.