Radiation-Hydrodynamic Models of the evolving Circumstellar Medium around Massive Stars

TL;DR

This study uses radiation-hydrodynamic simulations to explore how massive stars shape their surrounding medium, revealing the impact of stellar evolution phases, rotation, and thermal conduction on bubble structures and X-ray emissions.

Contribution

It provides new insights into the formation of circumstellar structures around massive stars, highlighting the roles of stellar evolution phases, rotation, and thermal conduction in shaping these environments.

Findings

Stellar rotation significantly affects wind bubble structures.

Thermal conduction slightly reduces bubble size but does not alter structure formation.

Models with clumpy bubbles have lower X-ray luminosity and softer spectra.

Abstract

We study the evolution of the interstellar and circumstellar media around massive stars (M > 40M_{\odot}) from the main sequence through to the Wolf-Rayet stage by means of radiationhydrodynamic simulations. We use publicly available stellar evolution models to investigate the different possible structures that can form in the stellar wind bubbles around Wolf-Rayet stars. We find significant differences between models with and without stellar rotation, and between models from different authors. More specifically, we find that the main ingredients in the formation of structures in the Wolf-Rayet wind bubbles are the duration of the Red Supergiant (or Luminous Blue Variable) phase, the amount of mass lost, and the wind velocity during this phase, in agreement with previous authors. Thermal conduction is also included in our models. We find that main-sequence bubbles with thermal conduction are slightly smaller, due to extra cooling which reduces the pressure in the hot, shocked bubble, but that thermal conduction does not appear to significantly influence the formation of structures in post-main-sequence bubbles. Finally, we study the predicted X-ray emission from the models and compare our results with observations of the Wolf-Rayet bubbles S\,308, NGC\,6888, and RCW\,58. We find that bubbles composed primarily of clumps have reduced X-ray luminosity and very soft spectra, while bubbles with shells correspond more closely to observations.