The evolutionary history of the Magellanic Clouds has been very different from that of the Galaxy. As a result we presently observe major differences between both the stellar content and the cluster populations in the Galaxy and the Clouds.

The evolutionary history of the Magellanic Clouds has been very different from that of the Galaxy. As a result we presently observe major differences between both the stellar content and the cluster populations in the Galaxy and the Clouds.

The introduction of new photometric techniques for faint objects has tremendously increased our understanding of the MC clusters, especially at the old end of the age spectrum. Many of the well-studied clusters of the past have gone through several transformations, starting as true globulars in 1960, becoming intermediate-age objects in the 1970's, but now returning to the true globular classification in the 1980's. LW 868 is an example of a cluster with such a history. Better photometric accuracy is also greatly improving our understanding of younger clusters, allowing detailed comparisons with theoretical evolutionary models, and a more reliable determination of the age-abundance relationship. The dynamical history of MC clusters can also be examined from the new data. The cluster formation rate, as well as the destruction rate, can be reconstructed from modern, deep cluster surveys.

This paper reviews the attempts that have been made to derive the ages and compositions of star clusters from studies of their integrated light. It discusses what can be learned by such methods regarding the history of the Magellanic Clouds. Finally, it reviews what is known about the age-spread and abundance-range in the cluster-systems of other galaxies and considers the history of the Magellanic Clouds in this context.

Plates taken with the 1.2m U.K. Schmidt Telescope and the 3.8 AAT Telescope have been used in order to derive the dynamical parameteres of 43 various clusters of the SMC by means of star counts. The clusters are divided into two main categories: (i) the disk, “blue” and “intermediate” in colour, young, mainly globulars and (ii) the halo, “red”, old globular clusters. The disk clusters have been found to be more massive and older than the galactic open clusters, whereas the halo clusters are at least 10 times less massive than the galactic globulars. The relaxation times of the disk clusters are larger than their evolutionary age while the observed density profiles always show evidence of well relaxed systems.

We have measured the ellipticities of 52 globular clusters in the LMC and 93 in the Galaxy by eye from polaroid enlargements of the sky surveys (Frenk & Fall 1982). In most cases, the measurements pertain to regions between (1–2)rh where rh is the median radius of a cluster; i.e. the radius containing half of the light in three dimensions. These were compared with determinations based on star counts for 12 members of the LMC sample and 19 members of the Galactic sample. We found no systematic difference between the ellipticities from the two methods and concluded that the eye-measurements are free of any major bias. They are also in reasonable agreement with the measurements by Geyer & Richtler (1981) and Geyer, Hopp & Nelles (1983), who used the Agfa contourfilm technique. The ellipticities measured by Geisler & Hodge (1980) from microdensitometer scans are systematically large in comparison with our results and those of Geyer and his associates. Since the scans cover only a small part of each cluster, a few bright stars can cause spurious elongations in the fitted contours.

The globular clusters in the Large Magellanic Cloud offer an unique possibility for the study of their spatial structures. Their ages show a very wide range from 6·107 to >5·109 years which is unknown for their galactic counterparts. The latter ones are all very old and therefore dynamically relaxed systems, whereas the young globular clusters of the Magellanic Clouds (age <108 years) have still preserved the dynamical state with which they were formed (Geyer et al. 1979). Furthermore, these young globulars show in their Hertzsprung-Russell diagram morphology the massive and luminous stars still on the main sequence with only a few evolved red supergiants. As in general the luminosity of the individual stars depends on their evolutionary state, the total mass to total luminosity ratio of a stellar cluster represents also its evolutionary state.

Ages of six intermediate-age Large Magellanic Cloud star clusters have been estimated using the time dependent behavior of the luminosity of stellar interior models of red giants. All clusters studied, NGC 1783, NGC 1868, NGC 1978, NGC 2121, NGC 2209, and NGC 2231, were found to have ages < 109 yr. It is concluded that there is currently no substantial evidence for a major cluster population of large, populous clusters > 109 yr in the Large Magellanic Cloud.

We present metallicities for the young LMC clusters NGC 1818, 1866 2157, 2136 and 2214. This sample is increased by taking over additional values from literature, so for NGC 1850, 1994, 2004, 2100 from the list of Hodge (1981). The intention is to compare these values with metallicities found in a field population of comparable age. Such a population may be represented by bright Cepheids, for which metallicities based on Washington photometry (Harris 1983) are available. The only young SMC cluster, for which we could estimate a metallicity, is NGC 330. Therefore, a comparison with SMC Cepheids, whose metallicities are also quoted by Harris (1981), can lead to uncertain statements only, until further observations of young SMC clusters will have been made.

The complex NGC 1962–65–66–70 is one of the many giant filamentary shell nebulae in the LMC. The nebulosity, also known as N144 was studied originally in H-alpha by Henize (1956). It has an angular size of 698″ x 620″ and surrounds an association of very young blue stars. The cluster has been studied first photographically in V and B by Westerlund (1961).

Preliminary results are presented of a search for RR Lyrae variable stars in old clusters in the Magellanic Clouds. RR Lyraes have been found in NGC 1786 and NGC 2210. With the exceptions of NGC 339 (SMC) and NGC 2019 and Hodge 11 (LMC), all clusters classified as type VII by Searle, Wilkinson and Bagnuolo (1980) contain RR Lyrae variables. On the other hand, none have yet been found in clusters of type VI.

The period changes of RR Lyrae stars can be compared with models of horizontal branch stars as a means of investigating the physical properties of the stars themselves, and of the stellar systems in which they are found (Smith and Sandage 1981). The present study is the first in which period change rates of extragalactic RR Lyraes have been estimated.

A program of electronographic photometry of star clusters in the Magellanic Clouds is being carried out using the McMullan camera on the Danish 1.5-m telescope at La Silla. The observations are being reduced using the Geneva microdensitometer and data reduction programs. Results are shown for the LMC cluster Hodge 11 (=SL 868), based on measurements of two exposures in both yellow and blue-light, each three hours in length, recorded on Ilford L4 emulsion.

The age of the star cluster H11 has been controversial for a number of years. The color-magnitude diagram (CMD) of Walker (1979) to V=21.5 was interpreted as an “…evolved main-sequence, whose termination point corresponds to an age of about 0.6 Gyr, but with a giant branch which is displaced blueward by about Δ (B-V)o=0.4 from the positions of the giant branches of open clusters of similar age in our Galaxy.” On the other hand, the integrated colors are similar to those of metal-poor globular clusters in the Galaxy (Freeman and Gascoigne 1977, and references therein), and “…incompatible with an age of say 0.3 Gyr.” Searle, Wilkinson and Bagnuolo (1980) classify it as Group VII, the oldest group. The system has no RR Lyrae stars (Graham and Nemec 1984).

The globular cluster Kron 3 in the Small Magellanic Cloud presents an interesting opportunity to study stellar evolution in a population of intermediate age populous enough to contain many stars in short-lived phases of their evolution. The cluster lies approximately two degrees west of the body of the SMC and just outside the tidal radius of the Galactic globular cluster 47 Tuc.

We summarize B,V imagery results from the CTIO 4-m telescope and two electronic detectors: (1) The SIT vidicon at the R-C focus yielded pixels in the 0.82 or 1.1 arcmin2 frames (Harris, Hesser and Atwood 1983). (2) KPNO's P-F CCD (used by McClure and Hesser) gave 0.6 pixels in 3×5′ fields. (The latter data are being analyzed in cooperation with Stryker and Nemec, who observed some of the same objects.) Zero points for the CCD data are set by observations of E region standards and of giants in Galactic star clusters.

The large number of star clusters in the Large Magellanic Cloud provides us with an excellent opportunity to understand well this neighboring galaxy. The large variety of integrated cluster colors present suggests a wide range in evolutionary stages, and several studies have established vague relationships between their location in the LMC and properties including color, total luminosity and metallicity.