A search for Ejecta Nebulae around Wolf-Rayet Stars using the SHS H$\alpha$ survey

TL;DR

This study re-examines the surroundings of Wolf-Rayet stars using the SHS Hα survey, identifying new ejecta nebulae, analyzing their characteristics, and comparing their occurrence across different galactic environments.

Contribution

It introduces new criteria for identifying WR ejecta nebulae and reports the discovery of a new nebula around WR 8, enhancing understanding of WR star environments.

Findings

A new nebula around WR 8 was discovered.

Approximately 5-6% of WR stars have ejecta nebulae.

Most ejecta nebulae are associated with nitrogen-rich WN stars.

Abstract

Recent large scale Galactic Plane H$\alpha$ surveys allow a re-examination of the environs of Wolf-Rayet (WR) stars for the presence of a circumstellar nebula. Using the morphologies of WR nebulae known to be composed of stellar ejecta as a guide, we constructed ejecta nebula criteria similar to those of Chu (1991) and searched for likely WR ejecta nebula in the SHS H$\alpha$ survey. A new Wolf-Rayet ejecta nebula around WR 8 is found and its morphology discussed. The fraction of WR stars with ejecta type nebulae is roughly consistent between the MilkyWay (MW) and LMC at around 5-6%, with the MW sample dominated by nitrogen rich WR central stars (WN type) and the LMC stars having a higher proportion of carbon rich WR central stars (WC type). We compare our results with those of previous surveys, including those of Marston (1997) and Miller & Chu (1993), and find broad consistency. We investigate several trends in the sample: most of the clear examples of ejecta nebulae have WNh central stars; and very few ejecta nebulae have binary central stars. Finally, the possibly unique evolutionary status of the nebula around the binary star WR 71 is explored.