We present new UV, visual and Hα photometry obtained with the WFPC2 of NGC 330, NGC 1818, NGC 2004 and NGC 2100, four young populous clusters in the MCs. We present observational evidence for a degree of convective core overshoot in excess of that currently applied in standard models.

Color-magnitude diagrams reaching from the giant branches to Vlim ~ 27.0, or about three magnitudes fainter than the turnoff, have been obtained in V and I with WFPC2 on HST for NGC 2419, Pal 3, Pal 4 and Eridanus, whose relative ages are discussed.

Binary clusters account for more than 10% of the cluster population in the Magellanic Clouds. Statistically fewer than 50% of the found pairs are expected to be chance superpositions. We are studying binary cluster candidates in the Magellanic Clouds to investigate whether the cluster pairs are of common origin and if they show evidence for interaction. We determine ages for the cluster components through isochrone fitting (isochrone models based on Schaerer et al. 1993, and Bertelli et al. 1994) to the colour magnitude diagrams (CMDs). We investigate the stellar spatial density in the surroundings of the clusters to look for signs of possible interactions between the components.

The study of star cluster pairs in the Magellanic Clouds (MCs) has been explored extensively in the past years (Bhatia & Hatzidimitriou 1988; Rodrigues et al. 1994; de Oliveira et al. 1998). The evolution of these pairs can provide fundamental insight into the past history of cluster formation in the MCs.

We have selected MC clusters (Bica & Schmitt 1995; Bica et al. 1998) with morphologies resembling those of the present models. The images in this selection of pairs were obtained from the Digital Sky Survey (DSS). We have also performed N-body simulations of star cluster encounters under different initial conditions, with the total number of particles per simulation ranging from 1024 to 20480.

We present our analysis of archival Hubble Space Telescope Wide Field Planetary Camera 2 (WFPC2) observations in F450W (~B) and F555W (~V) of the intermediate-age populous star clusters NGC 121, NGC 339, NGC 361, NGC 416, and Kron 3 in the Small Magellanic Cloud. We use published photometry of two other SMC populous star clusters, Lindsay 1 and Lindsay 113, to investigate the age sequence of these seven star clusters in order to improve our understanding of the formation chronology of the SMC. We analyzed the V vs B–V and MV vs (B–V)o color-magnitude diagrams of these populous Small Magellanic Cloud star clusters using a variety of techniques and determined their ages, metallicities, and reddenings. These new data enable us to improve the age-metallicity relation of star clusters in the Small Magellanic Cloud. In particular, we find that a closed-box continuous star-formation model does not reproduce the age-metallicity relation adequately. However, a theoretical model punctuated by bursts of star formation is in better agreement with the observational data. The full details of this analysis are reported in Mighell, Sarajedini, & French (1998, AJ, 116, 2395).

The faint star cluster AM-3 is one of three such objects discovered by Madore & Arp (1979). AM-1 has since been shown to be one of the most distant of the Galaxy's halo globular clusters, while AM-2 is now recognized as a distant, reddened Galactic open cluster. AM-3, however, has been largely ignored despite the fact that it lies only ~4.5 degrees from the center of the SMC making association with the SMC a possibility. This possibility was strengthened by the results of Irwin (1990) who showed that AM-3 lies (in projection) just within the outermost density contours of the SMC field population.

We present deep HST color-magnitude diagrams of fields centered on the six old LMC globular clusters NGC 1754, NGC 1835, NGC 1898, NGC 1916, NGC 2005, and NGC 2019. Separate cluster and field star CMDs are shown. The time of formation of the LMC is studied from an analysis of the cluster CMDs. Based on a comparison of the CMDs with sequences of the Milky Way clusters M3, M5, and M55, we suggest that the LMC formed its first stars at the same time as the Milky Way to within 1 Gyr. We find additional evidence that these LMC globular clusters are as old as the oldest Milky Way clusters through a comparison of our data with the horizontal branch evolutionary models of Lee, Demarque, & Zinn (1994).

The evolution of the LMC following its formation is studied through an analysis of the field star CMDs. Through an automated comparison with stellar evolution models, we extract the star formation histories implied by the CMDs. Our best-fit star formation histories imply that the LMC has been actively forming stars over the last 4 Gyr, in agreement with previous field star studies. The four fields that lie in the Bar also contain significant numbers of stars with ages of 4–8 Gyr in the best-fit cases. The most notable disagreement between the best-fit models and observed CMDs is in the color of the red giant branch.

We used deep HST imaging of three LMC clusters, NGC 2257, NGC 1466 and Hodge 11, to determine their ages relative to Milky Way clusters. They all have similar ages to within ± 1 Gyr. For NGC 2257 and NGC 1466, we measured the blue straggler specific frequencies and find them to be similar to those of Galactic clusters.

A method has been developed for the detection of stellar complexes and the derivation of their fundamental properties in the LMC. We have used digitized UKST plates in order to perform star counts and produce isodensity contour maps in various colours and luminosity slices. About 50 large stellar groupings have been revealed. Their properties favour a “top-down” mechanism acting in star forming regions.

Large interstellar distances imply that protostars are dynamically decoupled from gas ram pressure (see, e.g., Aarseth, Lin & Papaloizou 1988) and are effectively isolated self-gravitating objects. With this in mind we apply Newtonian gravity to collapsing cold spheroids of point masses to model the Lin-Mestel-Shu (1965) solution for dust. Incomplete violent relaxation (e.g., van Albada 1982) means that traces of the initial orbit distribution in energy remain. We show here that furthermore the degree of orbit mixing achieved correlates well with initial morphology, by collapsing two-mass component uniform spheroids of different aspect ratio. We setup a test problem to seek out a relation between orbit survival and initial morphology which we then solve numerically.

The supergiant shell LMC 4 is known for its ring of HII regions and the deep minimum in HI in the interior (Rohlfs et al. 1984). LMC 4 shows X-ray emission detected by ROSAT and highly ionised gas (C IV) detected with HST (Bomans et al. 1994, 1996). The velocities of its neutral gas indicate it cannot have been formed by the collision with a high velocity cloud (Domgörgen et al. 1995).

We have constructed a dynamical model of the LMC to examine the effects of an off-center bar perturbation on the global distribution of the gas and star formation activity. We find that a weak rotating bar potential, whose center is displaced by 0.6 kpc from the disk center, gives rise to an asymmetric spiral structure which mimics the observed chains of recent star formation as well as activity in the bar region.

We present details of the database from a large Cycle 7 HST project to study the formation and evolution of rich star clusters in the LMC (see Elson et al., this volume). Our data set, which includes NICMOS, WFPC2 and STIS images of 8 clusters, will enable us to derive deep luminosity functions for the clusters and to investigate the universality of the stellar IMF. We will look for age spreads in the youngest clusters, quantify the population of binary stars in the cores of the clusters and at the half-mass radii, and follow the development of mass segregation.

UBV measurements of resolved stars in the associations of two Magellanic irregulars, Leo A and Sextans B, are compared with synthetic color-magnitude diagrams based upon stellar evolutionary models.

Recently, Demers & Battinelli (1998) have shown that the young intercloud stellar aggregates are 10 to 25 Myr old, thus younger than the estimated age (200 Myr) of the last close LMC–SMC encounter (see, e.g., Irwin et al. 1996). These stellar aggregates show a distance gradient that confirms the existence of a “link” between the two Magellanic Clouds. Numerous blue stars have been detected by Demers & Irwin (1991) east of the aggregate ICA76 (the closest to the LMC). These blue stars, that extend to the southwestern periphery of the LMC, may be an aftermath of the close LMC–SMC encounter. Our present study is aimed to survey this SW part of the LMC and to determine the origin of these blue stars.

We present the results of a study of the stellar population around SN1987A in the Large Magellanic Cloud based on an analysis of multi-band HST-WFPC2 images.

We compare the luminosity function of star clusters in the LMC and NGC 4449: a IBm/Sm type galaxy very similar in appearance and luminosity (MB = −18.5) to the LMC (MB = −18.4). The brightest of several hundred clusters in NGC 4449 have MV = −10 (assuming a distance of 3.9 Mpc), comparable to the brightest clusters in the LMC.

A new age calibration of Cepheids and supergiants is used to study the large-scale recent star formation history of the LMC and the SMC. We find evidence for migration of star formation along the LMC bar as well as for the existence of long-lived (≈ 200 Myr) extended star-forming features.

The proper motion of the LMC relative to three background QSOs has been determined. 125 CCD frames taken from 1989.0 to 1997.2 at the Cassegrain focus of the CTIO 1.5 m telescope were used. The method of observation and reduction is breafly presented. The results are compared with those obtained by other authors who use different methods and proper motion reference systems. We find a good agreement in μαcosδ, but a rather large discrepancy in μδ. Our LMC proper motion seems to indicate that the LMC is not leading the Magellanic Stream.

Considerable progress has been made in the current decade with the help of N-body simulations towards a deeper understanding of the nature of the dynamical relationship between the Large and Small Magellanic Clouds and the Galaxy. The origin of such features as the Magellanic Stream, the inter-Cloud Bridge, the Wing and large extension in depth of the SMC has come to be interpreted in the context of the tidal interactions among the members of the LMC-SMC-Galaxy triple system. The inclusion of gas-dynamical effects and star formation in the latest models has added further refinements to this picture and confirmed the enhancement of the star formation rate in the SMC as a result of the recent LMC-SMC encounter.