Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...18111501g&link_type=abstract
American Astronomical Society, 181st AAS Meeting, #115.01; Bulletin of the American Astronomical Society, Vol. 24, p.1302
Astronomy and Astrophysics
Astronomy
Scientific paper
We present CTIO imaging and spectroscopy of newly-discovered shell nebulae around the LMC Wolf-Rayet stars Breysacher 13 (WN4) and Breysacher 2 (WN1). The spectrum of the Br 13 shell appears similar to that of normal LMC H II regions, except that the [N II] and He I lines are significantly stronger, while the [S II] lines appear weaker. We derive an electron temperature of about 17,000 K for the Br 13 shell; at this temperature O/H is a factor of 10 smaller and N/O a factor 15 higher than standard LMC ISM values; the helium abundance is nearly a factor of two higher as well. The electron temperature may be affected by the presence of partial shocks as have been seen in wind-blown bubbles (Dufour 1989, RMxA 18, 87), in which case we underestimate the oxygen abundance; however, T_e would have to be as low as 5,000 K to obtain a normal N/O ratio, and the helium abundance is nearly independent of temperature. Therefore, we are convinced that the Br 13 shell represents enriched stellar ejecta similar to the Galactic nebula NGC 6888. High-resolution imaging and spectroscopy will be required to separate any shocked material from the photoionized component in order to refine the derived abundances. In contrast, the shell associated with Br 2 has O, N and He abundances which are very close to the LMC ISM values. Therefore, we suggest that the Br 2 shell is a wind-blown feature within the larger N79 complex. The spectrum is remarkable for the strength of the nebular He II lambda 4686 line (first identified by Pakull 1991, IAU Symposium 143), which approaches 70% of the Hβ strength in some places. This testifies to the very hot nature of the WN star.
Chu Y.-H. Y.-H.
Dopita Mike A.
Garnett Don R.
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