We are deriving BV color-magnitude diagrams of star clusters in two selected regions in the SMC. These zones, characterized by the presence of a high density of star clusters, are centered at the 1981 coordinates for region 1: (RA: 1h, Dec −73°08′), and for region 2: (RA: 1h 10m.33, Dec −73°00′). See Figure 1 for their identification relative to the SMC.

The International Ultraviolet Explorer (IUE) has been used by me since January 1979 to observe globular clusters in the LMC, under various IUE programs in collaboration with Art Code. A first report was presented at the NASA 2nd IUE conference in 1980 (de Boer 1981a). A comparison of the UV colors for 11 MC clusters with the colors of galactic globular clusters was presented during IAU Colloquium 68 (de Boer 1981b), in a review which accumulates also all references to literature on far-UV photometry of galactic globular clusters. Using the VILSPA data base Cacciari et al (1982) repeated the comparison. The spectra of three clusters with good signal were presented by Code (1982). Data for a few other clusters were reported by Cacciari and Fusi-Pecci (1981) and by Cassatella and Geyer (1982; and this symposium).

The young populous star clusters give evidence for the ‘explosive’ star formation in the Magellanic Clouds which took place in the time interval 5·106 yrs to < 108 yrs agoe. They are also key objects for the understanding of the formation of massive stellar clusters, because they are still situated close to their ‘birthplace’ in the parent galaxy and are dynamically not relaxed (Geyer et al. 1979). Their HRD-morphology shows most of the member stars in the upper Main Sequence range with only a few massive yellow and red supergiants. The lower massive stars are still in the pre-main-sequence evolution phase (‘T-Tauri state’), which cannot be observed at the MC's distances. Thus in the uv-spectral range the blue stars with (B-V) < 0.1 on the upper MS contribute to the uv-fluxes. In the optical spectral regions the bright ‘blue’ globular clusters seem not be embedded in remanent interstellar matter, though neighbouring loose stellar aggregates of similar age are in many cases surrounded by dense HII-regions. This rises the questions wether the starformation process in such massive clusters was so efficient that no remanent matter was left over, or was this material blown away by the uv-radiation of the numerous OB-member stars?

The globular clusters NGC 1786 in LMC and NGC 121 and 330 in SMC have been observed in UV with IUE, both in the long and short wavelength range, in the low dispersion mode. The spectra show stellar component(s) superimposed on the cluster contributions.

We have studied high a low resolution IUE spectra of O and B stars in the LMC cluster NGC 2100, the SMC cluster NGC 330, and the young Galactic cluster NGC 6530. Temperatures and luminosities were determined. In the LMC and SMC clusters the most luminous stars are evolved stars on the “horizontal” supergiant branch, while in NGC 6530 the stars are all still on the main sequence.

Extinction laws were determined. They confirm the known differences between LMC and galactic extinctions.

No mass loss was detected for the evolved B stars in the LMC and SMC clusters, while the high luminosity stars in NGC 6530 show P Cygni profiles.

Following Larson and Tinsley the integrated colours of the MCs from the UV to the red can be used to obtain the ratio of the present rate of star formation to the total amount of stars formed. Other tracers of recent star formation (number of bright stars, of supernova remnants, Hα emission, etc…) will be used to determine the present rate of star formation and to obtain some information on the initial mass function. The recent (t < a few 107 years) history of star formation in the MCs will then be discussed. Finally, it is found that the ratio present rate/total amount of stars ever formed is of the order of 0.1 Gyr−1 for both Clouds, implying a rather uniform average rate of star formation if the Cloud ages are the order of 1010 years. The results will be confronted with the metallicity-age relation and the age distribution of stars and clusters.

One of the most fundamental questions we might ask about galaxies is, Do all galaxies have the same age? A less general question, and one which we can surely succeed in answering is, Are the Magellanic Clouds (MCs) the same age as the Galaxy? We must also make clear what is meant by the same age if, in fact, star forming activities in these systems have proceeded along different timescales. The age of a system can be masked if the strongest star-forming epoch was not coincident with the initial epoch. Deep colour-magnitude diagrams (CMDs) and luminosity functions (LFs) have had to wait until the advent of large southern telescopes, sensitive emulsions and detectors, and accurate methods of measuring crowded images.

Nearly all places in the LMC where ring nebulae or shell structures in the neutral or ionized interstellar medium are observed, an OB association and/or WR-stars can be located (Braunsfurth, Feitzinger, 1983). Several mechanisms have been propsoed to generate shell or bubble structures: stellar winds, supernovae explosions, evolving HII regions, sequential starformation, collapsing hydrogen clouds interacting with stellar winds and radiation pressure. Ordered motions resulting in a shell or bubble structure are the result of almost any point like energy injection into the interstellar medium. Therefore all the mechanisms result in similar morphological structures, thus similar shapes can have heterogeneous origins.

From far-UV to visible integrated photometry of the Magellanic Clouds we give an estimate of the past star formation parameters. Most of our results can be applied to Irregular galaxies.

Methods used in pattern recognition and cluster analysis are applied to investigate the spatial distribution of OB associations and emission regions in the LMC. For our analysis we used the catalogue of associations of Lucke and Hodge (1970) and the catalogue of emission regions of Davies et al. (1976).

According to the stochastic self propagating star formation theory (SSPSF, Gerola and Seiden, 1978), the star formation process in galaxies changes from a fluctuating but continuous mode to a bursting one, when the size of the system becomes relatively small (R ≤ 3 Kpc). Then, due to its size, the LMC should be a system undergoing fluctuating but continuous star formation activity, whereas the SMC should be in the region between continuous and bursting modes (Gerola et al. 1980). In order to look better inside this problem a model of chemical evolution of the two Clouds, which takes into account the stochastic star formation rate, has been built. For the SMC both the continuous and the bursting modes of star formation have been considered. As a result we find that the different chemical histories of the two Clouds may be related to the fact that SMC has undergone several bursts of star formation (between 50 and 60), while a continuous star formation activity was present in LMC.

Star counts in a number of fields near the Large Magellanic Cloud have shown a maximum extension of about 10° for the faint stars. The luminosity function in the outer regions of the LMC is consistent with an intermediate age population.

An area in the LMC situated 1.2 degrees from the centre of the Bar has been studied with the ESO 3.6 m telescope using electronography and photoelectric measurements for calibration. Coordinates for 1950.0 are 5h20m, −71°. Six exposures have been used, with exposure times ranging from 8 to 90 min. Typical seeing was 1.5 arcseconds FWHM. This investigation is a continuation of our earlier study with the ESO 1.5 m telescope (Lindgren et al., 1980).

A colour magnitude diagram of a field in the south-west periphery of the SMC reveals a population similar to that obtained earlier in another field, with an age of 3 × 109 years. The present field is from the SMC centre, more than a degree more distant than the first one. The similarity in stellar content between the two emphasises the widespread nature of this population.

A search for faint stars (to in B) in a bright part of the Magellanic Stream designated MSI by Mathewson (1976), carried out from automatic scans of UKST photographs by means of the COSMOS machine gives a negative result as far as the main HI cloud is concerned, but reveals a small surplus of images in a patch 1 degree away from the main HI concentration.

Observations of the Large Magellanic Cloud obtained with the 10-channel ultraviolet photometer of the OAO-2 are presented. The aperture was circular and 10 arcmin in diameter whereas the wavelength coverage was from 4250 to 1430Å. A total of 50 fields has been measured. Using photometric criteria, the data fall into three groups which are also spatially separated. The different characteristics are easily understood in terms of population and reddening differences, but only if the previously reported MLMC extinction law” (Koornneef and Code 1981; Nandy et al. 1980) is adopted.

Why are the kinematics and dynamics of the Magellanic Clouds worth studying ? Some of the reasons are:

1. 1. The Clouds are the closest examples of Magellanic systems. These asymmetric systems give some interesting dynamical problems. Because the Clouds are so close, a unique amount of information can be obtained on the kinematics of objects of all ages. This should be very helpful for understanding the dynamics.

2. 2. The Clouds and the Galaxy are interacting. This produces complex kinematics of the gas in and between the Clouds, and also the Magellanic Stream. Again, very detailed information can be derived. We would like to know enough about the gas dynamics of interacting galaxies, to be able to explain the kinematics produced by this interaction.

3. 3. The interaction will affect the star formation and chemical evolution in the Clouds. As new results are obtained on the star formation history and the chemical evolution, it is important to follow in parallel the dynamical history of the system, to see if the dynamics, star formation and chemical evolution can be tied together.

A brief survey is made of recent 21-cm and optical observations of the Magellanic Stream(MS). The space orientation of the Magellanic Clouds is touched upon in relation to modelling the MS. After summarizing a variety of models for the MS, we show that if our Galaxy is massive with a huge dark halo, a tidal model is most suitable for reproducing its characteristic structure and high-negative radial velocity. Past orbits of the Large and the Small Magellanic Cloud (LMC and SMC) are determined uniquely for the last 2×109 yr, if we postulate that the LMC and SMC are bound together for 1010 yr: Highly-noncircular motion of the SMC around the LMC could give a clue to understand some peculiar features associated with the Magellanic Clouds.

The global distribution of HI in the Magellanic System is shown in Figure 1. The gas covers some 1500 square degrees of sky and has a mass of 1.8 × 109 M⊙. There are four main components: the LMC, the SMC, the inter-Cloud region and the Magellanic Stream. The integrated HI of the first three components is mapped in Figure 2 with the Parkes 64-m radio telescope which has a resolution of 15 arc min. The previous surveys of McGee and Milton (1966), Hindman (1967), Mathewson et al. (1979) have been combined with a recent survey by Mathewson et al. (1983) of the outer regions of the System to give this large-scale picture of the gas distribution. The last two surveys were made with a velocity resolution of 4.12 km s−1 and a minimum detectable signal of 0.2 K. The long spurs extending from the LMC and SMC and the bridge joining the two galaxies with prominent spurs pointing to the Magellanic Stream are all compelling evidence for tidal interaction between the LMC and SMC (Mathewson 1976a, Murai and Fujimoto 1980). The detailed velocity field of the HI is given in Mathewson et al. (1983). Its large-scale features are shown in Figure 5 of Mathewson et al. (1979) which indicate that the radial velocities of the inter-Cloud region form a velocity continuum with those of the LMC and SMC. This plus the continuity of the general velocity gradient across the entire Magellanic System strongly suggest that the two galaxies are bound.