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We report the results of optical spectroscopy of the blue supergiant Sk-69279 and its circular shell in the Large Magellanic Cloud (LMC) with theSouthern African Large Telescope (SALT). We classify Sk-69 279 as an O9.2 Iafstar and analyse its spectrum by using the stellar atmosphere code CMFGEN,obtaining a stellar temperature of \approx 30 kK, a luminosity oflog(L_*/Lsun)=5.54, a mass-loss rate of log(\dot{M}/(Msun/yr))=-5.26, and awind velocity of 800 km/s. We found also that Sk-69 279 possesses an extendedatmosphere with an effective temperature of \approx 24 kK and that its surfacehelium and nitrogen abundances are enhanced, respectively, by factors of\approx 2 and 20--30. This suggests that either Sk-69 279 was initially a(single) fast-rotating (\ga 400 km/s) star, which only recently evolved off themain sequence, or that it is a product of close binary evolution. The long-slitspectroscopy of the shell around Sk-69 279 revealed that its nitrogen abundanceis enhanced by the same factor as the stellar atmosphere, which implies thatthe shell is composed mostly of the CNO processed material lost by the star.Our findings support previous propositions that some massive stars can producecompact circumstellar shells and, presumably, appear as luminous blue variableswhile they are still on the main sequence or have only recently left it.

Optical spectroscopy of the blue supergiant Sk-69 279 and its circumstellar shell with SALT