OFPE/WN9 circumstellar shells in the Large Magellanic Cloud.

Abstract

In order to investigate the circumstellar shells of four luminous Of-like objects in the LMC, high-resolution, 4 m echelle spectrograms were obtained. The most striking characteristic of the Ofpe spectrum is the presence of velocity-doubled nebular lines, which are very strong in H alpha and N II forbidden lines at wavelengths 6548 and 6583. Analysis of these lines indicates enhanced nitrogen abundance relative to hydrogen and oxygen, in comparison with H II regions of the LMC. These expanding shells might be regarded as supergiant planetary nebulae, and they likely provide another example of nitrogen enrichment by massive stars. In order to resolve the question of whether these spectra should be classified as Ofpe or WN9, low-dispersion blue-violet spectrograms of two additional LMC stars and three in the Galaxy are presented. A definitive decision is difficult for several reasons, but some constraints are placed on the answer.