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A New Ejecta Shell Surrounding a Wolf-Rayet star in the LMC

Donald R. Garnett and You-hua Chu
Publications of the Astronomical Society of the Pacific
Vol. 106, No. 700 (1994 June), pp. 626-631
Stable URL: http://www.jstor.org/stable/40680313
Page Count: 6
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A New Ejecta Shell Surrounding a Wolf-Rayet star in the LMC
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Abstract

We have obtained CCD spectra of newly discovered shell-like nebulae around the WN4 star Brey sacher 13 and the WNl star Brey sacher 2 in the Large Magellanic Cloud. The shell around Br 13 shows definite signs of enrichment in both nitrogen and helium, having much stronger [N ii] and He i emission lines than are seen in typical LMC H ii regions. From the measured electron temperature of about 17,000 in the shell, we derive He/H and N/O abundance ratios which are factors of 2 and more than 10 higher, respectively, than the average LMC interstellar values. The derived oxygen abundance in the Br 13 shell is down by a factor of 8 compared to the local LMC ISM; however, the derived electron temperature is affected by the presence of an incomplete shock arising from the interaction of the stellar wind with photoionized material. This uncertainty does not affect the basic conclusion that the Br 13 shell is enriched by processed material from the Wolf-Rayet star. In contrast, the shell around Br 2 shows no clear evidence of enrichment. The nebular spectrum is characterized by extremely strong [O iii] and He ii emission and very weak [N ii]. We derive normal He, O, and N abundances from our spectrum. This object therefore appears to be simply a wind-blown structure associated with a relatively dense cloud near the Wolf-Rayet star, although the very high-ionization state of the gas is unusual for a nebula associated with a Wolf-Rayet star.

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