Ring Nebulae around LBVs and WR stars

Summary

Abstract

WR stars and their precursors, the LBVs, represent the late stages of evolution of hot, massive stars, and are often surrounded by ring nebulae. These are believed to be formed either by the action of the stellar wind, a past, episode of violent ejection from the star, or a combination of these two processes. The various research applications of LBV and WR nebulae are reviewed, particularly with regard to the information they provide on the central stars. Abundance studies show that N overabundances and O deficiencies are a general feature of ejecta around evolved massive stars. Observations of bipolarity in LBV nebulae provide valuable clues to wind asymmetries in the central stars. The nebulae can also be used to derive stellar effective temperatures through photoionization modelling. Finally, the connection between LBV and WR nebulae from an observational point of view is discussed.

Introduction

The ring nebulae that are observed around Luminous Blue Variables (LBVs) and Wolf-Rayet (WR) stars are examples of circumstellar media in the late stages of stellar evolution of hot, massive stars. These nebulae are excellent laboratories for studying the interaction of winds and ejecta with the interstellar medium (ISM). They also provide unique insights into the central stars, particularly from an evolutionary point, of view. In Sect. 2, LBVs and WR stars are introduced, and Sect. 3 discusses the formation and composition of their nebulae. Sect.