As an introduction to the symposium the related problems of the distances, structures and chemical compositions of the Magellanic Clouds are reviewed.

It is traditional to begin a review on the subject of the Magellanic Clouds with a discussion of the distance of the Clouds. Feast did this in his introductory remarks to the meeting, and I shall not resist the temptation to reflect a little on this subject. At the Tubingen meeting we gave some thought to a new controversy between a (short) distance modulus of 18.2 for the LMC and the more traditional (Long) distance of 18.7. The short distance was primarily the result of main sequence fitting to LMC clusters resulting from new CCD photometry. A consensus has arisen since that time, and is represented at this meeting by results presented by Walker and Caldwell, and earlier by Reid and Strugnell (1986) and recently by Jacoby et al. (1990), that the best value of (m-M)o is 18.45±0.15 for the LMC (which is also the average of the short and long values). This is obtained, however, by given low weight to (firstly) recent work on the absolute magnitude of RR Lyrae stars based on the Baade-Wesselink technique and (secondly) the aforementioned main sequence fitting results

A vast amount of observational data concerning the structure and kinematics of the Magellanic Clouds is now available. Many basic quantities (e.g. distances and geometry) are, however, not yet sufficiently well determined. Interactions between the Small Magellanic Cloud (SMC), the Large Magellanic Cloud (LMC) and our Galaxy have dominated the evolution of the Clouds, causing bursts of star formation which, together with stochastic self-propagating star formation, produced the observed structures. In the youngest generation in the LMC it is seen as an intricate pattern imitating a fragmented spiral structure. In the SMC much of the fragmentation is along the line of sight complicating the reconstruction of its history. The violent events in the past are also recognizable in complex velocity patterns which make the analysis of the kinematics of the Clouds difficult.

The relations between the distributions of interstellar gas and young stars in the central parts of the SMC are discussed, based on their distributions over the sky, radial velocities and distances. There are large differences between stars and gas. The existence of two main complexes is confirmed. There is no strong evidence for a distance in depth between these complexes larger than about 10 kpc, although Cepheid observations suggest a large total depth in some regions. Further, more accurate observations of Cepheids, especially of their mean radial velocities, are required for a better understanding of the structure of the SMC.

New radio continuum surveys of the Large and the Small Magellanic Cloud have been completed recently at four frequencies, using the Parkes 64-m telescope. Here we shall discuss briefly the overall radio morphology of the Clouds at different frequencies and discuss the detected linear polarization. A preliminary integrated radio continuum spectrum of the Large Magellanic Cloud is also presented. Various aspects of future studies will be outlined.

We report the results of a comprehensive reanalysis of the X-ray imaging data for the Large Magellanic Cloud obtained with the Einstein Observatory. A map covering 37 deg2 of the Cloud is presented. The total 0.15–3.5 keV luminosity is ˜ 5 × 1038erg s--1, two thirds of which can be attributed to the 105 identified discrete emitters and the remainder of which arise from the coronal component of the interstellar medium at temperatures from ˜ 2 to ˜ 10 × 106K. The energy balance for this hot ISM and the morphology of specific regions such as 30 Doradus and LMC-2 are briefly discussed.

Molecular gas is a major constituent of the interstellar medium of all late-type galaxies. Virtually all of it is in the form of cold molecular hydrogen (H2) which today cannot be observed directly. However, the tracer molecule carbon monoxide (CO) (relative abundance 10−5) is easily detected. For the Magellanic Clouds (MCs), CO studies are of specific importance. The Clouds are rich in HI, and if we can establish the presence of significant amounts of H2 as well, this will influence our estimates of the global rate of star formation and its history. Complexes of presently quiescent molecular gas may betray regions primed for star formation, but not yet in action. Detailed studies of the HI, HII and H2 and young star content may provide estimates of star formation efficiences on scales of a kiloparsec.

Surface distribution contour maps of the HB/clump population and the < 1 Gyr main sequence population for the outer regions of the Small Magellanic Cloud (SMC) are presented. Aspects of the stellar population synthesis, large-scale structure and evolutionary history of the SMC halo are discussed.

The structure of the Large Magellanic Cloud (LMC) has posed many questions and has led to many controversial discussions. Although classified as an 'irregular', repeated claims have been made suggesting that the LMC has spiral structure. Furthermore, this 'spiral' structure seems to originate in the 30-Doradus nebula which, as a result, was sometimes referred to as the 'nucleus' of the LMC. We summarize the recent data on the LMC and re-examine the HI data to point out that possibly different rotation centres exist for different components.

The dust content of the Magellanic Clouds can be studied using optical, ultraviolet, infrared and, indirectly, radio wavelength data. All recent studies show that the dust content is lower than that of the Milky Way Galaxy for both Clouds and that the optical properties of the dust are different. At ultraviolet wavelengths, the 2165 Å “bump” in the extinction curve is significantly smaller than in the Galaxy (this now appears NOT to be a consequence of the lower heavy element abundances) and the far ultraviolet (shortward of ˜2000 Å) extinction is greater than in the Galaxy (this IS likely to be a consequence of the lower heavy element abundances). New optical data on background galaxies suggest that the total extinction in the central parts of both the LMC and the SMC is approximately 1.5 magnitudes. High local extinction values are derived from uv and optical observations of star-forming regions, where a spatial correlation with CO detections is sometimes, but not always, found.

Here we discuss current observational data on, and the distribution of, neutral hydrogen in the Large Magellanic Cloud (LMC).

We introduce an as yet unpublished set of OAO-II observations of stellar associations in the Large Magellanic Cloud (LMC). Cross-correlation of the photometric characteristics of these fields with the infrared fluxes at these same positions obtained by the IRAS satellite provides information on the local stellar population, the amounts of interstellar extinction and thermal dust emission.

Initially, carbon stars have been searched for through their CN bands in the near infrared. However, C stars can also be identified efficiently by the C2 Swan bands in the blue-green spectral region. Schmidt telescopes with objective-prisms have been used intensively for the detection of C stars. More recently, transmission gratings at the prime foci of large telescopes have made possible deeper surveys at limiting magnitudes that insure carbon star detection in the Magellanic Clouds (MCs) with a reasonable degree of completeness; completeness is even better in the regions where both observational techniques have been used. Statistical studies are now possible. The C star surface distribution and global kinematics derived from radial velocity measurements of selected C stars, when compared to those of other objects, show that the field Small Magellanic Cloud (SMC) C stars are not a young population, in agreement with studies of C stars in SMC clusters.

Velocities have been measured for 74 CH stars in the direction of the Large Magellanic Cloud (LMC). These have been used to study the kinematics of the oldest stellar population. Velocities of these objects appear to reflect two distinct subgroups - one associated with the old globular cluster population and a second with the LMC disk.

A recently completed study of the kinematics of Long-Period (or red) Variables (LPVs) in the LMC by Hughes et al. (1990) has shown that those with short periods (100 to 225 days) have spheroidal kinematics (high velocity dispersion and low rotational velocity about the LMC). This is the first evidence of the LMC's possessing a spheroidal population. The spheroid is flattened (with axial ratio c/a ˜0.3 to 0.5), and is not much thicker than the intermediate age disk. The velocity distribution of the old LPVs indicates that the mass of the LMC is ˜ 6.2 ± 1.5 × 109M, and that of the spheroid represented by the old LPVs is ˜2 % of the LMC's total mass. If these old LPVs are members of the LMC's disk, then their velocity dispersion implies that they have an age of ˜10 Gyr. The LPVs with intermediate periods (225 to 450 days) are members of the LMC's rotating disk population, with an age ˜4 Gyr derived from their velocity dispersion, and similar to that of the planetary nebulae, CH stars and old cluster populations.

The Small and Large Magellanic Clouds (SMC, LMC) are of considerable interest from a kinematical viewpoint. The tidal interation of the Clouds with each other and with the Galaxy appears to have been quite significant in recent times (Murai & Fujimoto 1980). The SMC in particular appears to have been considerably disrupted by a recent close passage to the LMC (Mathewson & Ford 1984, Mathewson 1984, Mathewson et al. 1986). For the LMC Freeman et al. (1983) found that the young and old populations have significantly different rotation solutions.

Planetary Nebulae (PN) form a population with age intermediate between the HI and young clusters and the old Population II clusters. A large number of PN are known in the MCs. Sanduleak et al. (1978) compiled a list of 102 in the LMC and 28 in the SMC. Since then other authors have increased the total number known to approximately 140 in the LMC and 50 in the SMC.