The observable Metal-enrichment of Radiation-driven+Wind-blown HII Regions in the Wolf-Rayet Stage
From stellar evolution models and from observations of Wolf-Rayet stars it is known that massive stars are releasing metal-enriched gas in their Wolf-Rayet phase by means of strong stellar winds. Although HII region spectra serve as diagnostics to determine the present-day chemical composition of the interstellar medium, it is not yet reliably explored to what extent the diagnostic HII gas is already contaminated by chemically processed stellar wind matter. In a recent paper, we therefore analyzed our models of radiation-driven and wind-blown HII bubbles around an isolated 85 Msun star with originally solar metallicity with respect to its chemical abundances. Although the hot stellar wind bubble (SWB) is enriched with 14N during the WN phase and even much higher with 12C and 16O during the WC phase of the star, we found that at the end of the stellar lifetime the mass ratios of the traced lements N and O in the warm ionized gas are insignificantly higher than solar, whereas an enrichment of 22% above solar is found for C. The transport of enriched elements from the hot SWB to the cool gas occurs mainly by means of mixing of hot gas with cooler at the backside of the SWB shell.