A classification of star clusters in the Magellanic Clouds

Abstract

Four-color photometry of the integrated light from 61 star clusters in the Magellanic Clouds, together with a rediscussion of Danziger's multivariate spectrophotometric data for some of these same clusters, have made possible for the first time an intelligible classification scheme for their integrated spectra. It is found that the integrated spectra of populous star clusters in the Magellanic Clouds may be arranged in a one-dimensional sequence in such a way, that on traversing the sequence, all spectral features behave regularly - not necessarily monotonically, but as smoothly as can be expected from the magnitude of observational error. The character of the spectral variations along the sequence suggests that both cluster age and chemical composition vary smoothly as the sequence is traversed. The newly discovered sequence is distinctly different from the analogous one for star clusters of the Galaxy, and this fact is interpreted as indicating that the relation between epoch and average chemical composition of the interstellar medium is qualitatively different in different stellar systems.