Spectral classification of O and B0 supergiants in the Magellanic Clouds

Abstract

A spectroscopic study has been made of the brightest known O, OB + WN, and B0 supergiants in the Magellanic Clouds, based upon wide high-resolution classification spectrograms. Among the interesting LMC objects are found the third known O3 supergiant and a superluminous late-O nitrogen supergiant. Also noteworthy are four peculiar Of stars with pronounced low-excitation envelopes, which have no exact counterparts identified in the Galaxy. An example of the numerous compact multiple systems among these stars is shown in which a W-R component has been identified by interference-filter photography. In the SMC, further evidence for large metal deficiencies is provided by two luminous B0 supergiants, which have Si/He line ratios similar to those in galactic stars of luminosity class IV. Possible evidence for a similar but smaller effect in the LMC is given in terms of a systematic discrepancy between the Si/He luminosity classes and derived absolute magnitudes. The absolute magnitudes of the normal Of stars in both Clouds confirm the supergiant nature of such objects, previously inferred from galactic observations. Twelve of the most interesting spectrograms are reproduced.