Recent observational results for dwarf spheroidal galaxies are reviewed and discussed. In particular, the differences in stellar populations between dwarf spheroidal galaxies and globular clusters are highlighted. It seems most probable that the origin and evolution of dwarf spheroidal galaxies was very different from that of globular clusters.

Information is currently available for globular cluster systems in almost 50 galaxies from the Milky Way to the Coma Cluster. The observed features of these systems are reviewed, with emphasis on (a) their total populations (specific frequencies), (b) spatial structures compared with the underlying halo light, (c) photometric characteristics (luminosity function and metallicity). The combined evidence suggests strongly that globular clusters are likely to have formed in a rather sharply defined epoch clearly before the bulk of the halo field stars, and that this epoch was more active in E galaxies, especially those in rich environments. Finally, the special role of the supergiant E's at the centers of rich galaxy clusters is reviewed.

We review early and recent photometric studies of the M87 globular cluster system. We also describe recent high quality spectroscopic studies that have been used both to measure the metallicities of M87 globular clusters and to determine the mass of M87's halo.

Globular clusters have a sufficiently distinct character that we can treat the system of globular clusters, as a distinct object which has a size, mass and angular momentum, but also, an internal density distribution, velocity distribution, and, in general, a detailed interior structure. Shapley, of course, pioneered in the effort to model, that is to describe, the existing state of the system from our vantage point. At the present time we probably have an inventory of clusters which is largely complete, and for the majority of the identified systems we have good knowledge (cf for example Webbink, 1985) of positions in the galaxy, one component of galactic velocity and a sufficiently detailed picture of the interior dynamical state to characterize each cluster by a luminosity and two radii: a core radius rc where the surface density has fallen to half the central value, and a tidal radius rt determined by a fit to the King (1966) truncated isothermal profiles, which is thought to represent the radius beyond which the tidal force due to the galaxy effectively exceeds the force due to the clusters own gravity.

The influence of tidal heating on the evolution of globular clusters (GC's) in circular orbits about the Galactic center is studied. Giant Molecular Clouds (GMC's) stretch a globular cluster in a direction transverse to its orbit through the disk. The variation in acceleration with height in the disk compresses the cluster in a longititudinal direction. Numerical and analytic calculations of heating and mass loss for GC's, represented by King models, show that disk heating dominates. We apply the results to calculate GC evolution prior to core collapse or tidal disruption using a three parameter (energy, mass, and tidal radius) sequence of King models. The changes in the parameters are calculated for tidal perturbations, relaxation and evaporation. Clusters close to the Galactic center (less than 3 kpc) undergo core collapse in a Hubble time. The effect of tidal perturbations on energy and mass loss of the cluster is strongest between 3 and 5 kpc where it can substantially effect the evolution of the cluster. Here, depending upon their initial concentration, clusters are either tidally heated and dissolved, or forced towards a gravothermal catastrophe in times that are a fraction of a Hubble time. These inner regions of the Galaxy should be fertile territory for the search for post-collapsed clusters.

The investigation of globular cluster swapping in clusters of galaxies has resulted in some interesting theoretical findings and, at the same time, it offers a promising field for observers. Numerical simulations of galaxy clusters where the galaxies have swarms of test particles around them showed that, in addition to tidal stripping, tidal accretion plays an important role in the dynamical evolution of clusters of galaxies; it also turns out that, even in clusters where the gravitational field is dominated by a massive background, the galaxy-galaxy attraction cannot be ignored when estimating the outcome of collisions. Cluster swapping is just an example of tidal accretion and, taking the globulars as probes of halo material, it might offer an opportunity to observe some consequences of that effect; besides, although the difficulties look formidable at present, the study of globulars lost through tidal stripping is a possibility that should not be neglected. Tidal stripping and accretion processes are very sensitive to the ratio of galactic mass to total mass, so that observations related to the cluster swapping phenomena may provide a new means to investigate the missing mass problem.

A primary motivation for studying globular clusters is that, as the oldest known galactic fossils, they trace the earliest stages of galactic evolution; indeed, they may hold the key to understanding galaxy formation. Thus it is clearly of great importance to learn how to read the fossil record. To do this, we need to understand something about how the globular clusters themselves formed. Were they the first bound objects to form, or did they form in larger pre-existing systems of which they are just small surviving fragments? If the latter, what were the prehistoric cluster-forming systems like? And how did they manage to produce objects like globular clusters?

The purpose of this article is to review some recent attempts to understand the origin of globular clusters. To put this in perspective, it may help to recall the analogous problem of the origin of galaxies. This splits into two parts. First, given a proto-galaxy with a specified mass and radius, how does it collapse, form stars and settle into a state of dynamical equilibrium? Richard Larson explored these topics in an important series of numerical simulations in the 1970s. Progress in this area brings into sharper focus a second set of questions that really has precedence over the first. Why did proto-galaxies have properties like the initial conditions in the collapse calculations and what distinguishes galaxies from structures on much larger and much smaller scales? Similar questions face us when we consider the origin of globular clusters. First, how did stars form in a proto-cluster, what was the efficiency, the initial mass function and so forth? It is appropriate that Larson has discussed these topics in the preceding article but here we are mainly concerned with the second kind of question: What is special about objects with masses of order 105-106 M⊙ and dimensions of a few tens of parsecs?

Much of what we know about the structure, dynamics, and evolution of globular clusters derives from their observed density profiles, and their interpretations. In this review, I will briefly describe the problems and techniques specific to the surface photometry of globular clusters, show some new results, and offer suggestions for future ground-based work.

X-ray binaries in globular clusters provide a powerful tool for the exploration of the evolution of compact binaries and their host globular clusters. Recent x-ray and optical studies of these systems have yielded long-sought binary periods and fundamental properties for two sources (in NGC 6624 and M 15). It appears that tidal capture formation of compact binaries in globular clusters can proceed by several different routes and lead to exotic systems such as the white dwarf-neutron star binary with an 11-minute period recently discovered in NGC 6624. Combined with previously reported long-term periods for several globular cluster (and field) x-ray sources, this suggests again that many of these systems may in fact be hierarchical triple systems. The prospects for forming these in the dense cores of clusters undergoing core collapse is discussed, and searches for color gradients in the cores of globular clusters showing cusps in their central surface brightness distribution are presented. A program to test for the high central density of binaries (and triples) expected in cusp clusters by searching for diffuse line emission from their constituent cataclysmic variables is briefly described. Finally, the case for globular cluster disruption and the formation of galactic x-ray burst source is reviewed in light of recent developments.

Density profiles of most globular clusters are well fitted by a King (1966) model. The evolution of a King model in the tidal gravitational field of the Galaxy is first discussed. If the concentration parameter c (= log(rt/rc)) is small enough, the evolution is nearly along the King model sequence and c becomes larger. When c becomes large enough (about 2.1), gravothermal instability sets in. The basic properties of gravothermal instability is next discussed. The stability criterion and its interpretation are given. Globular clusters consist of stars with disparate masses, so that finally the evolution of multi-component clusters is discussed. Acceleration of evolution in multi-component clusters and equipartition of the kinetic energies among components are discussed, and conclusions and future problems are given.

As our understanding of core collapse in globular clusters has improved through detailed computer simulations, attention has naturally turned to dynamical evolution of globular clusters after core collapse. The results of recent simulations of post-collapse cluster evolution are reviewed. An assessment is given of progress towards the goal of developing astrophysically realistic models that cover all phases of globular cluster evolution. A focus of this review is the stability of the post-collapse expansion phase to the large amplitude core oscillations first observed in the simulations of Sugimoto and Bettwieser and now confirmed by several other studies. The implications of core oscillations for the observation of post-collapse clusters are discussed.

We present a procedure which allows to predict the dissolution times of star clusters in a simple way. The dissolution time of a cluster depends mainly on its total mass, its median radius and its galactic environment (galactic tidal field and passing massive objects). As an example, we discuss the lifetimes of LMC clusters. Finally, we show that massive black holes, which have been proposed as the major constituent of the dark coronae of galaxies, are very effective in destroying globular clusters.

The source for intracluster matter is seen in various mass loss processes ongoing within clusters and is supported by the theoretical need for mass loss to explain the morphology of cluster colormagnitude diagrams. A variety of techniques ranging from X-ray to radio wavelengths have been employed to search for such matter but with few exceptions has not been found. The amount of material expected to collect between cleansing passages through the galactic plane has variously been estimated at between ∼ 102 and ∼ 103 M⊙. In contrast, observed upper limits for many clusters are well below these values, often > 1 M⊙. The few detections are at levels of ≲10−2 M⊙.

This review will consist of two parts: (a) a brief description of a new method to determine Vo, the circular speed of the local standard of rest, and which, of course, plays a fundamental role in the mass distribution of the Galaxy, and (b) a review of the globular clusters as tracers of the mass distribution in the Galaxy.

So much has been learned already, during these last four days, about globulars that I shall start by addressing the second part of my topic first: the primordial chemical composition. Then I shall review the abundance of the primordial elements in globulars, or more generally in Population II. Actually if the globulars are the oldest stars ever observed in the Universe one could hope that the subject is over and that there is no need to speak about elements synthesized in stellar interiors for globulars. Unfortunately these rascals show always some amount of stellar nucleosynthesis products and this may very well be the central problem raised by their chemical composition. We shall discuss in turn the amount of the stellar synthesized elements in globulars and then the clues given by the pecularities of the abundance ratios, which may help in understanding their origin. The last section summarized the present knowledge of the subject.

Globular clusters (GC) have been regarded among the most obvious targets for the Hubble Space Telescope since the very first conception of this project, and some observational programs have been exemplified in publications concerning the future use of HST (e.g. Westphal 1982 and Macchetto 1982, in the “Patras Book”, Bahcall 1985, see also the 1985 Report of the STScI working group on Stars and Star Clusters).

The high angular resolution of the Hubble Space Telescope will provide opportunities for many fundamental observations of globular clusters, most of which have been extensively discussed in the literature. We have therefore chosen to devote our time (and pages) to a presentation of what HST observations may reveal about some aspects of galactic globular clusters. To avoid infringing upon programs that others may propose, we have limited ourselves to simulations of observations that are part of our Guaranteed Time Observations. [The complete catalog of GTO observations has published by the Space Telescope Science Institute and is available upon request.]

This was a really exciting conference! The main problem in summarizing it is that so many new and important results were presented, making it impossible to mention each one individually. In reviewing this conference I shall first discuss new results, then problem areas revealed by papers and during discussions and finally desiderata and trends for future work.

This exhibit featured facsimiles of some letters that Shapley exchanged with George Ellery Hale, Henry Norris Russell, and Heber Doust Curtis from 1917 when he was at Mount Wilson working on globular clusters to 1921 when he became Director of Harvard College Observatory.