STAR-CLUSTERS IN THE CLOUDS OF MAGELLAN

Star clusters in the Magellanic Clouds differ from those in the Galaxy in a number of important respects: 1. Both old and young clusters in the Clouds have radii r(h) that are typically 3-4 times larger than those of their Galactic counterparts. 2. Luminous clusters of all ages in the LMC and the SMC are, on average, significantly more flattened than Galactic clusters. 3. The clouds contain a class of populous star clusters, with masses that are typically an order of magnitude smaller than those of average globulars, but an order of magnitude larger than those of most Galactic open clusters. 4. Many young clusters in the Magellanic Clouds are embedded in rich unbound stellar coronae. Such halos are probably the remnants of the associations in which these clusters were born. Stellar coronae around clusters can survive longer in the Clouds than in the Galaxy because tidal forces are much lower in the LMC and SMC than they are in the Galaxy. 5. The Large Cloud is surrounded by at least seven real globular clusters with ages greater than 10 Gyr (six of which contain RR Lyrae stars), whereas the Small Cloud has only one such companion. These clusters have luminosities and mass-to-light ratios similar to those of Galactic globulars. All six of the Large Cloud globular clusters for which color-magnitude diagrams are available have blue horizontal branches. This may indicate that these objects all have very large ages. Available data do not yet entirely exclude the possibility that these globular clusters belong to a spheroidal halo. 6. The specific globular cluster frequency is found to be S = 0.4 +/- 0.15 for the LMC, and S = 0.3 +/- 0.3 for the SMC. 7. In both the Large Cloud and the Small Cloud old clusters are found to be more widely distributed than are younger clusters. Known old clusters (and nova) exhibit no concentration to the Bar of the LMC. 8. Both the metal enrichment history and the ages of star clusters indicate that star formation in the SMC got off to a slow start. The large residual gas mass in the Small Cloud also indicates that the Small Cloud never went through an intense prolonged starburst phase. No Large Cloud clusters are presently known with ages between about 3 and 10 Gyr. The end of this hiatus may have coincided with a major burst of star formation in the LMC. 9. The fact that the two largest bursts of star and cluster formation in the LMC appear to have no counterparts in the SMC indicates that the bursts of star formation in the Large Cloud were not triggered by close encounters between the Clouds.