Radiation Hydrodynamics of Line-Driven Winds

TL;DR

This paper reviews the physics of radiation-driven winds in massive stars, focusing on the CAK model, instabilities, and challenges in modeling mass loss and variability.

Contribution

It advances understanding of radiative driving mechanisms and discusses complexities like instabilities and wind initiation near the sonic point.

Findings

Analysis of the CAK model and its limitations

Discussion of wind instabilities and saturation effects

Challenges in modeling mass loss rates and variability

Abstract

Dimtri Mihalas' textbooks in the 70's and 80's on "Stellar Atmospheres" and "Foundations of Radiation Hydrodynamics" helped lay the early groundwork for understanding the moving atmospheres and winds of massive, luminous stars. Indeed, the central role of the momentum of stellar radiation in driving the mass outflow makes such massive-star winds key prototypes for radiation hydrodynamical processes. This paper reviews the dynamics of such radiative driving, building first upon the standard CAK model, and then discussing subtleties associated with the development and saturation of instabilities, and wind initiation near the sonic point base. An overall goal is to illuminate the rich physics of radiative driving and the challenges that lie ahead in developing dynamical models that can explain the broad scaling of mass loss rate and flow speed with stellar properties, as well as the often complex structure and variability observed in massive-star outflows.