We discuss the integrated colours, kinematics, formation, dynamical evolution and initial mass functions of the young globular star clusters in the Large Magellanic Cloud (LMC). Because these clusters are so young, they offer us insights, unobtainable from the old globular clusters in our Galaxy, into the formation and early dynamical evolution of globular clusters.

A sample of Large Magellanic Clouds (LMC) and Small Magellanic Clouds (SMC) clusters for which ages have been directly determined from main sequence turnoff photometry has been compiled. According to this sample, the LMC and SMC cluster age distributions are very different. The LMC contains a large population of 1 to 3 Gyr old clusters as well as a small number of clusters that appear to be as old as the Galactic halo globular clusters. Surprisingly however, only a single cluster is known with an age in the interval between 3 Gyr and the age, taken as 15 Gyr, of the oldest clusters. The SMC age distribution, on the other hand, is much broader. It extends back to approximately 12 Gyr but there appear to be no SMC clusters as old as the oldest in the LMC. The sample of clusters is also used to discuss the age-abundance relations for both galaxies. Little can be learned for the LMC but it appears that the chemical evolution of the SMC differed in form from that experienced in the solar neighbourhood. The first results of an imaging survey designed to find LMC clusters with ages exceeding 3 Gyr are also described.

The massive star clusters of the Large Magellanic Cloud (LMC) are ideal laboratories for the study of the dynamical evolution of rich stellar systems. Not only do they contain large numbers of stars but, unlike the Galactic globular clusters, LMC clusters span a large range in age. Here we describe a continuing project to determine the temporal evolution of the mass-to-light (M/L) ratio of LMC clusters and present some preliminary results.

We present the age distribution function for Large Magellanic Cloud (LMC) clusters obtained from a relationship between their integrated U BV colours and age. We discuss further the results by Chiosi et al. (1988) on the nature of the bimodal distribution of the (B - V) colours for LMC clusters. Their conclusion that bimodality in the colour stems from the combined effect of the age distribution function and the rate at which clusters change colour with age, is revisited. The result of our analysis shows that the age distribution is the sole agent and that a real age gap is present. Finally, we draw some conclusions about the efficiency of cluster formation and disruption in the LMC.

The 843 MHz radio survey of the Magellanic Clouds with the Molonglo Observatory Synthesis Telescope (MOST) has provided continuum images with a resolution of about 45 arcsec for many HII regions. By comparing these radio data with H-alpha data regions of non-thermal emission may be found within HII regions.

New identifications of the Hα-emission-line objects in the Small Magellanic Cloud (SMC) have been made with the Curtis Schmidt telescope at Cerro Tololo Inter-American Observatory (CTIO).

A colour-magnitude diagram (CMD) of the region containing the intermediate-age SMC globular cluster NGC 152 was published recently (Melcher & Richtler 1989). A particularly interesting feature of this CMD is the “clump” of He-core burning stars, which are predominantly field stars. A selection of stars near the cluster centre leads to the CMD shown in Figure 1. The vertical extension of the clump (explainable by the evolution of stars younger than 1 Gyr) is replaced by a “tilted horizontal branch” (we use this expression for lack of a better one). The age of NGC 152 is about 1.3 Gyr and the reddening is small; the metallicity is unknown but less than −0.6 dex, which is the mean metallicity of the young SMC population. The tilted HB can be reproduced in CMD simulations using the method developed by Vallenari et al. (1990), and thus can be considered as a normal feature of star clusters like NGC 152. It is evident also in other intermediate-age MC clusters like Kron 3 (Rich et al. 1984).

High-precision radial velocity measurements have been obtained for 62 stars in the young LMC cluster NGC 1866 using the Las Campanas 2.5m with échelle spectrograph. The mass-weighted mean-square velocity dispersion is σ2 = 6.5 ± 1.3 km2 s−2. The mass of the cluster M(r < 20) = 8.1 ± 1.6 × 104M⊙, implying a M/L of 0.20 ± 0.04 in solar units.

Four candidate protostars have been identified, with luminosities of 1-5×'l04L⊙ and masses of 10-20M⊙, in a magnitude-limited near-infrared survey of the 30-Dor complex. Each is associated with a dense knot in the nebular arcs. We suggest that both the knots and the associated star formation result from the compression of interacting arcs of mass-loss winds from hot massive stars in the central cluster and other nearby clusters. This mode of star formation appears to be highly efficient. In the 30-Dor region there is a clear spatial separation of the young blue stars and older red stars, strengthening the evidence for a multiple starburst in the region.

Images with subarcsec spatial resolution in the light of near-infrared atomic (Bry) and molecular hydrogen H2 (S(1) v=1-0) emission lines were obtained for some extended, pointlike objects in the Large Magellanic Cloud (LMC) for the first time. We used the Max-Planck-Institut für extraterrestrische Physik (MPE) near-infrared array spectrometer FAST (image scale 0.8”/pix, spectral resolving power 950) at the ESO/MPI 2.2m telescope, La Silla. We present some results on the 30-Dor complex and N159A5.

Using U BV CCD photometry, the stellar content of HII regions and young star clusters in the Magellanic Clouds has been studied: (1) the reddenings have been determined, and ages of OB associations and young star clusters have been measured; (2) the stellar initial mass functions have been determined by using the main-sequence luminosity functions; and (3) U BV CCD surface photometry of nine young star clusters has been obtained and their structural properties investigated.

The aim of our project is to study the star-formation history in open clusters and field stars in two regions on either side of the bar of the Large Magellanic Cloud (LMC). In a forthcoming paper we shall describe the observations and the characteristics of the clusters. Here, we summarise the results of the BV photometry of three of the cluster fields: LW 55 (4h46.m6, −73°30'), HS 96 (5h03.m4, −65°57') and SL 196 (5h03.m6, −65°54', epoch 1950). They were all observed with an RCA CCD at the 2.2-m telescope at La Silla.

The projected velocity dispersion in the core of the Large Magellanic Cloud (LMC) intermediate-age globular cluster NGC 1978 is deduced from integrated light spectra. A numerical cross-correlation technique gives a projected velocity dispersion σp(core) = 5.8±1.2 km s−1. Multimass anisotropic King-Michie dynamical models are applied to the observational constraints given by the surface brightness profile and the above central projected velocity dispersion. Depending on the model, the values obtained for the total mass of the cluster range from 0.36 to 1.44 106M⊙, corresponding to mass-to-light ratios M/LV ranging from 1.2 to 4.2 (M/LV)⊙, values typical of galactic globular clusters.

The observed central velocity dispersion of a stellar system is dependent on the mass distribution and the velocity distribution function. For the past several years a program has been undertaken to determine central velocity dispersions of LMC and SMC clusters for comparison with galactic clusters. The mass-to-light ratio (M/L) estimates so obtained should be considerably more accurate than those obtained by tidal arguments (Chun 1978, Elson & Freeman 1985).

Accurate radial velocities (mean error = 1.3 km s−1) have been obtained for a sample of K-type giants with the CTIO 4m telescope and échelle spectrograph with CCD detector. All of the stars observed were within two core radii of the cluster centre. Multiple observations at several epochs (1984 and 1989) were used to determine the velocity errors.

The central M/L in solar units has been estimated from single component isotropic King models (King 1966), with the assumption that the distribution of mass follows that of the light. Observed values for the total integrated light and core radius were taken from the literature (in particular, from Chun 1978, van den Bergh 1981, Mateo 1987).

In an attempt to investigate the large scale structure and dynamics of the old population of the LMC, we have obtained high precision radial velocities for three extremely outlying (10°-15° from the LMC center) globular clusters. Our results agree well with the results from Freeman et al. (1983) that the clusters move in a disk like system. Depending on the assumptions used we can put a lower limit to the LMC mass of about 0.5-2.5×1010M⊙

Merging of stellar systems is investigated by means of N-body simulations. We discuss the synchronization instability to trigger sudden merging, the origin of the ellipticity in the merger remnants, the distribution of stars in the halo, and the survival of the colour gradient of stars against the violent relaxation of the merging process.

We present the photometry of two clusters NGC 2164 and NGC 1850 located in the Large Magellanic Cloud (LMC). The ages are determined taking into account the presence either of convective overshoot or of semiconvection in the stellar models. The experimental luminosity functions are compared with the theoretical models.

The young globular clusters in the Magellanic Clouds offer a good number statistic and a reasonably wide mass interval which are required for the derivation of any statistically reliable slope of the Initial Mass Function (IMF). Elson et al. (1989) and Mateo (1988) are amongst those few who utilized this potential first. These authors, however, arrive at different conclusions. Elson et al. find quite flat mass function slopes in comparison with the values given by Mateo. Here we present IMF slopes based on B, V CCD photometry for four young LMC clusters, NGC 1711, 2004, 2164 and 2214 and discuss the effects on them of cluster metallicity and of uncertainties in the incompleteness of the data.

Based on Einstein IPC data, we have completed a census of X-ray emission from and around OB associations in the LMC. In addition to an apparent correlation of young, X-ray bright supernova remnants with recent star formation regions, we detect diffuse X-ray emission from over two dozen other associations; luminosities in the 0.16–3.5 keV band range from ˜ 3 × 1034 (the detection threshold) to ˜ 1036erg s−1. The mean X-ray luminosity of the ˜ 50 undetected associations is ˜ 1034erg s−1 and the emission from all associations contributes ˜ 4% to the total diffuse X-ray emission from the galaxy. Implications of this survey for ISM bubble evolution is discussed.

We present CCD observations of several faint regions of active star formation in the Magellanic Clouds. For the five regions for which we were able to obtain photometric data we have extended the luminosity function (LF) two orders of magnitude below the previous faint limit of 1037 erg s−1 (1). Our preliminary results indicate that the LF turns over at 1036 erg s−1 for the LMC and 1036.5 erg s−1 for the SMC. It is also apparent that much of the Ha emission fainter than 1036 erg s−1 is diffuse or filamentary in nature.