Chemical self-enrichment of HII regions by the Wolf-Rayet phase of an 85 M star

Free access article

Issue		A&A Volume 450, Number 1, April IV 2006


Page(s)		L5 - L8
Section		Letters
DOI		http://dx.doi.org/10.1051/0004-6361:200600020

A&A 450, L5-L8 (2006)
DOI: 10.1051/0004-6361:200600020

Letter

Chemical self-enrichment of HII regions by the Wolf-Rayet phase of an 85 M $_{\odot}$ star

D. Kröger¹, G. Hensler² and T. Freyer¹

¹ Institut für Theoretische Physik und Astrophysik der Universität Kiel, 24098 Kiel, Germany
e-mail: danica@astrophysik.uni-kiel.de
² Institute of Astronomy, University of Vienna, Türkenschanzstr. 17, 1180 Vienna, Austria
e-mail: hensler@astro.univie.ac.at

(Received 12 December 2005 / Accepted 24 February 2006 )

Abstract
It is clear from stellar evolution and from observations of WR stars that massive stars are releasing metal-enriched gas through their stellar winds in the Wolf-Rayet phase. Although HII region spectra serve as diagnostics to determine the present-day chemical composition of the interstellar medium, it is far from being understood to what extent the HII gas is already contaminated by chemically processed stellar wind. Therefore, we analyzed our models of radiative and wind bubbles of an isolated $85~{M}_{\odot}$ star with solar metallicity (Kröger et al. 2006, A&A, in preparation) with respect to the chemical enrichment of the circumstellar HII region. Plausibly, the hot stellar wind bubble (SWB) is enriched with $^{14}\mbox{N}$ during the WN phase and even much higher with $^{12}\mbox{C}$ and $^{16}\mbox{O}$ during the WC phase of the star. During the short period that the $85~{M}_{\odot}$ star spends in the WC stage enriched SWB material mixes with warm HII gas of solar abundances and thus enhances the metallicity in the HII region. However, 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. Important issues from the presented study comprise a steeper radial gradient of C than O and a decreasing effect of self-enrichment for metal-poor galaxies.

Key words: galaxies: evolution -- HII regions -- hydrodynamics -- instabilities -- ISM: bubbles -- ISM: structure

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