The observable metal-enrichment of radiation-driven-plus-wind-blown H II regions in the Wolf–Rayet stage

Abstract

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 M⊙ star with originally solar metallicity with respect to its chemical abundances. Although the hot stellar wind bubble (SWB) is enriched with 14 N during the WN phase and even much higher with 12 C and 16 O during the WC phase of the star, we found that at the end of the stellar lifetime the mass ratios of the traced elements 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.

Interaction of massive stars with their surroundings

“…2) The stronger the wind the higher the compresssion of the SWB-surrounding Hii region (Hensler et al 2008), what means that the Hii rgion does not increase according to the larger ionizing flux.…”

“…4) The regions contributing to the Hii region emission line spectrum are not solely limited to the photo-ionized shell around the SWB but also form from photo-evaporated gas at the trailing surface of the SWB shock front (Hensler et al 2008; and see fig. 2).…”