Two ring nebulae around blue supergiants in the Large Magellanic Cloud

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 aroundbluesupergiantsintheLargeMagellanicCloud.Thestar Sk 69 279 is classied as O9f and is surrounded by a closed shell with a diameter of 4.5pc. Our echelle observations show anexpansionvelocityof14kms 1 andahigh(Nii)6583A/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 approach- ing surface. The expansion velocity is 24kms 1 and the (Nii)6583A/Hisnotmuchhigherthanthatofthebackground emission.Thelackofnitrogenabundanceanomalysuggeststhat the expanding shell is an interstellar bubble with a dynamic age of 2 10 5 yr.