Hot star winds

Summary

Abstract

Radiation pressure driven wind theory as applied to OB and related stars is reviewed, beginning with the first detailed formulation of the theory by Castor, Abbott & Klein (1975). The character of the line acceleration term in the equation of motion is discussed. The main successes of the time-independent theory are noted, along with its failures which motivated the more recent development of time-dependent (shocked-wind) theory.

Introduction

An early result from ultraviolet astronomy was that OB stars with bolometric magnitudes brighter than M_bol ≃ −6 suffer significant mass loss (Snow & Morton 1976). At about the same time the framework was laid down by Castor, Abbott & Klein (1975; hereafter CAK) for what, has proved since to be a very successful theory of mass loss from OB and other similarly high-luminosity stars. In bare outline the physical model is a simple one in which the outward force able to overcome gravity is the pressure exerted by the hot star's radiation field on its own atmosphere. In practical application, complexity arises from the fact that it is overwhelmingly the scattering of radiation in spectral lines that, mediates the force (a point first appreciated by Lucy & Solomon 1970).