Two ring nebulae around blue supergiants in the Large Magellanic Cloud
* 1, 2,
Y.-H. Chu 2,
W.J. Duschl 1, 3 and
Received 4 March 1997 / Accepted 28 April 1997
Ring nebulae are often found around massive stars such as Wolf-Rayet stars, OB and Of stars and Luminous Blue Variables (LBVs). In this paper we report on two ring nebulae around blue supergiants in the Large Magellanic Cloud. The star Sk-69 279 is classified as O9f and is surrounded by a closed shell with a diameter of 4.5 pc. Our echelle observations show an expansion velocity of 14 km s-1 and a high [NII ] 6583Å/H ratio. This line ratio suggests nitrogen abundance enhancement consistent with those seen in ejectas from LBVs. Thus the ring nebula around Sk-69 279 is a circumstellar bubble.
The star Sk-69 271, a B2 supergiant, is surrounded by an H arc resembling an half shell. Echelle observations show a large expanding shell with the arc being part of the approaching surface. The expansion velocity is 24 km s-1 and the [NII ] 6583Å/H is not much higher than that of the background emission. The lack of nitrogen abundance anomaly suggests that the expanding shell is an interstellar bubble with a dynamic age of 2 105 yr.
Key words: stars: circumstellar matter stars: individual: Sk-69 271 stars: individual: Sk-69 279 stars: mass-loss ISM: bubbles Magellanic Clouds
* Visiting Astronomer, Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatories, operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.
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© European Southern Observatory (ESO) 1997
Online publication: April 28, 1998