CO first-overtone emission at 2.3 microns has been detected in six luminous emission-line stars in the Large Magellanic Cloud. Of these, HD 268835, Hen S12, and HD 38489 are B[e] stars, HD 37836 is a peculiar O supergiant, and HD 269953 and HD 269723 are G supergiants. CO overtone emission is therefore present in luminous stars with a very large range of effective temperatures. None of the CO emission stars is known to be a photometric variable suggesting that the CO overtone emission is relatively long-lived in these stars. The three LMC S Doradus variables do not show this emission. Circumstellar disks are required around the three B[e] CO emission stars and HD 37836 to account for their optical and ultraviolet spectra. The CO overtone emission is also likely to arise in these disks because disk densities can be high enough to collisionally excite CO overtone emission and shield the CO gas from direct stellar radiation, and circumstellar disks are expected to be relatively stable envelope structures. We propose that the stars showing CO overtone emission have the highest density disks, while similar objects lacking this emission have disk densities below that required to excite overtone emission (n_H_ ~ 10^9^ cm^-3^). HD 269599s and Hen S93 are found to be luminous stars with hot dust shells. Eight stars with He I 2.058 micron emission stronger than H I Brγ emission are helium-rich and are probably becoming Wolf-Rayet stars. Eight emission-line stars have M supergiant companions.
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McGregor et al. (1988) studied this question.