Measurements are made of broadband infrared photometry and 2.3-micron CO indices for 20 late-type supergiants in young Magellanic Cloud blue globular clusters and 12 late-type supergiants in southern galactic open clusters. New photoelectric B and V data for most of these stars are also presented. These data make possible comparisons between the infrared properties of late-type supergiants in the Galaxy and the Large and Small Magellanic Clouds. The galactic supergiant CO indices permit a mean galactic supergiant relation to be defined in the (CO)0 versus (J - K)0 plane. At a given (J K)0 color, the LMC supergiant CO indices are approximately 0.04 mag weaker than this mean galactic value. The 30 Doradus supergiants are found to follow the same sequence in the (CO)0 versus (J - K)0 plane as the other LMC supergiants. A preliminary theoretical analysis reveals that the CO indices in the LMC supergiants are consistent with these stars being deficient in heavy elements by a factor of approximately 3.
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McGregor et al. (1984) studied this question.