Variable and Nonspherical Stellar Winds in Luminous Hot Stars: IAU Colloquium 16911The conference was held in Heidelberg, Germany, in 1998 June. The proceedings will be edited by B. Wolf, A. W. Fullerton, & O. Stahl and published in the Springer Lecture Notes in Physics series.

Abstract

The winds of hot stars are generally understood to be driven by the absorption of momentum from the intense stellar radiation field by line transitions in the ultraviolet and farultraviolet regions of the spectrum. Observational diagnostics of these dense winds can be reproduced quite well for most early-type stars within the context of a “standard model,” in which the outflow is spherically symmetric, smooth, and steady. This model serves as a useful starting point for estimating global properties such as mass-loss rates and for investigating the various ways that winds interact with their local interstellar environments. However, there is abundant evidence that essentially all hot-star winds contain time-dependent structure on a variety of spatial scales. Observations of anisotropy, clumpiness, and variability contradict the assumptions of the standard model and imply that our understanding of mass loss via stellar winds is still incomplete. IAU Colloquium 169 was convened to review the observational evidence for variability and asphericity in hotstar winds; to discuss the physical processes that might cause such behavior; and to look for evolutionary consequences. The meeting was hosted by the Landessternwarte HeidelbergKonigstuhl, a venue that was fitting not only because 1998 marked the centennial of its founding, but also because of its enviable history as a center for hot-star research. The meeting attracted nearly 150 researchers from 26 countries. Over the course of four and one-half days, 62 oral review and contributed papers and approximately 70 poster papers were presented. The topics of these papers included both garden-variety OBA stars and their more exotic cousins: Be stars, Wolf-Rayet stars, and the rare B[e] stars and luminous blue variables (LBVs). The role played by rotation in shaping the emergence of the stellar wind was a recurrent theme in these presentations and also provides a framework for this brief report on the meeting. The proceedings contain comprehensive discussions of these and other highlights, which included reports of impressive progress in modeling disk winds; analysis and simulations of the nebulae ejected by hot stars in episodic mass-loss events; and distance determination from quantitative spectral analysis of the photospheres and winds of hot stars. Rotation is the most obvious, universal process that can induce large-scale asphericity in the stellar winds of single stars, and it is therefore not surprising that it was a focus for this