This review of observations is oriented toward the problem of core collapse in globular clusters. After a brief discussion of methods of determining surface densities, recent results are cited which show that the central brightness peak seen in M15 also appears in several other clusters. The central peaks of brightness are interpreted as the result of core collapse, which theories have repeatedly predicted. If binaries stabilize the collapsed core, the cluster should follow a Hénon model. In two of the three cases tested this model is a reasonable fit. Remaining theoretical questions are listed, as are observational needs.

We describe techniques and results for obtaining radial velocities and proper motions for individual stars in globular clusters. One set of these results for the nearby northern clusters M92 and M13 are discussed in terms of new dynamical models and distance estimators.

First I will describe briefly some older work on chemical gradients in globular clusters. Then I will discuss some more recent data on the chemical and kinematical properties of 47 Tuc and Omega Cen, that leave us in little doubt about the reality of such chemical gradients.

Recent studies of the x-ray sources in globular clusters have provided important new clues for both the dynamical processes in clusters and the stellar content and evolution of globular clusters. Very deep x-ray images of several globular clusters show evidence for diffuse x-ray emission from hot gas which may be related by a simple shock model to properties of both the cluster, such as its orbit in the Galaxy, and the interstellar medium in the halo of the Galaxy. The x-ray surveys conducted with the Einstein Observatory are reviewed and the results derived for the luminosity function, masses and nature of the compact x-ray sources are discussed. The evidence for the compact binary nature of the sources is now overwhelming, but long-term x-ray variability studies previously reported may suggest that some of the systems are in fact triple systems with distant companions. Possible relationships between the initial mass function, stellar density and cluster evolution are discussed, and our arguments that the ostensibly similar compact x-ray sources in the galactic bulge are remnants of a population of globular clusters disrupted by giant molecular clouds are updated.

We present a high spatial resolution photographic study of the core of some concentrated globular clusters (F.W.H.M. of averaged star intensity profiles reaches 0″.5 on the best plates). Good plates of M 79, M 53, M 3, M 5, M 13, M 92, NGC 6397, M 15, M 2 and M 30 were obtained (Aurière and Cordoni, 1983, Astron. Astrophys. Suppl. Ser. 52, 383 and references therein). The observations are mainly obtained at the 2 m and 1 m Cassegrain telescopes of Pic-du-Midi Observatory. The high spatial resolution of our plates enables us to achieve stellar photometry, at least for the bright stars, in these overcrowded regions. Surface photometry is also obtained.

Proper motion data of M13 cluster members are very useful for the investigation of the cluster's internal dynamics. We introduce a maximum likelihood method to fit these data in terms of conventional King-Michie models.

Observations made at Las Campanas Observatory and at the Anglo-Australian Observatory have been used to determine line-of-sight velocities with an average accuracy of 3 kms−1 for 135 member stars in the globular cluster 47 Tucanae. The velocities were derived from cross-correlation techniques applied to 30 A/mm spectra obtained with digital sky-subtracting detectors. The spectra themselves have been used to analyze the cyanogen anomalies on the red giant branch in this cluster (Norris et al., 1984). When combined with the velocities published by the CORAVEL group (Mayor et al., 1983), these observations yield velocities for 212 stars with projected distances from the cluster center ranging from 3 to 68 core radii. After radial binning and analysis these observations yield the following results:

(i) The inner parts of the cluster show appreciable differential rotation with a maximum projected rotation velocity of approximately 6 kms−1 in the region 6–18 core radii. However, at larger radii the rotation declines rapidly and is essentially zero for radii greater than 30 core radii. This result is illustrated in Figure 1. To within the errors of the determinations, the position angle of the maximum rotation and that of the major axis of the stellar density distribution coincide.

(ii) In contrast to M3 (Gunn and Griffin 1979), “thermal equilibrium” multimass models (c.f. Da Costa and Freeman 1976) can ONLY reproduce the observed velocity dispersion values by including a substantial amount of “dark matter”; i.e. unlike M3, there is “missing mass” in 47 Tuc. In order to retain a fit to the surface brightness profile of the cluster, this “dark mass” (which provides perhaps 30 to 40 percent of the total cluster mass) cannot have a distribution much different from that of the cluster giants if it is in the form of stars and “thermal equilibrium” is maintained. In this case the obvious candidates for the dark matter are the white dwarf remnants of the stars more massive than the current turnoff mass, though many more such remnants are required than the number expected from extrapolating the present mass function. The difference between M3 and 47 Tuc in this case then implies that the 47 Tuc initial mass function had many more massive stars than did that for M3. The work of Freeman (1977), who demonstrated large IMF variations in the 8 − 1.5 solar mass range in young Magellanic Cloud clusters, provides observational support for this interpretation.

We report the preliminary results of a surface photometry survey of globular cluster cores. Two new cores with post-collapse morphology have been found, and two possible candidates. The estimated fraction of clusters with this core morphology in the Galaxy is only a few percent. Most clusters do not show a morphology similar to the predictions of the central black hole models.

Core and tidal radii of the Carina dwarf galaxy are determined by fitting King dynamical models to number count radial profiles, derived from COSMOS data. These values are compared with those of the other six known Local Group dwarf spheroidals.

CCD photometry in B and V reaching B(lim) ≃ 25 has been employed to obtain the luminosity function and color-magnitude diagram for the main sequence of 47 Tuc. For 5<Mv<10 we find that its LF is essentially flat (Δlog n/Δm~0). The CMD is successfully matched by isochrones with [Fe/H] = −0.5 and t ≃ 15 × 109y.

The dynamical study of the SMC clusters is very important for many reasons. (a) The disk “blue” clusters are more massive and older than the galactic open clusters whereas the “halo” red clusters are less massive and younger than the galactic globulars (Kontizas, Danezis, Kontizas, 1982; Kontizas and Kontizas, 1983). (b) All clusters show density profiles that fit the available theoretical models (King, 1962) giving evidence of relaxed systems, even for the young clusters with evolutionary ages 106−108yr. The relaxation mechanism has to be reconsidered for the SMC and possibly in connection to the metal abundance. (c) The ellipticities of young and old SMC clusters have shown that there is no obvious age-ellipticity dependance and that the SMC clusters are statistically more elliptical than the clusters of the LMC and our Galaxy (Frenk and Fall, 1982, Kontizas et al, 1984).

UBVR CCD surface photometry for a sample of 11 globular clusters has been obtained at the Kitt Peak National Observatory (KPNO) #1 0.9 m telescope as part of a major study of globular cluster core structure. These data are being used to test for the presence of central cusps in the surface brightness profiles', which are expected to be present in clusters which have already undergone core collapse (Cohn and Hut 1984).

Thanks to numerous and accurate radial velocity measurements obtained with CORAVEL, the rotational velocity fields, the spatial velocity dispersions from the centre to the edge and the ordered to random motions ratios are deduced for two globular clusters: ω Cen and 47 Tuc. Masses through virial theorem and M/L ratios are also given. A more comprehensive study will be published in Astron. & Astrophys.

Globular clusters are among the most difficult types of objects to observe with standard photoelectric techniques. Among factors which may contribute to measurement error are the centering of apertures in the oftentimes diffuse cores of clusters, the random distribution of bright stars near the cluster centers, and the determination of an adequate sky correction in fields badly crowded by foreground stars. These problems have been well-discussed by a number of authors (see, e.g., Hanes and Brodie 1984, and the references they cite).

We have obtained 295 new radial velocities for the 112 giants in the globular cluster M3 previously observed by Gunn and Griffin. Our velocities have a typical accuracy of 0.8 km/s per measurement and have been combined with the Gunn and Griffin data in order to search for radial velocity variations over a time span of ten years. We find no convincing evidence that any of the giants observed are spectroscopic binaries with one notable exception, von Zeipel 164, which we believe is the first spectroscopic binary to be found in a globular cluster. Modelling of the velocity variations that would be expected in our data for a variety of binary populations confirms Gunn and Griffin's conclusion that binaries with separations of less than 10 AU must occur much less frequently among the giants of M3 than among the population I field stars.

Deep Hβ narrowband and broadband images of M3 have been electronically blinked to search for cataclysmic binaries. Tests of the method on a known, faint cataclysmic enable us to set limits on the sensitivity of the technique. No bright (MB < 6) emission-line (equivalent width > 12 Å) cataclysmic binaries exist in M3 between 4 and 30 core radii from the center. Low luminosity globular X-ray sources could still be weak-lined (E.W. < 12 Å) and bright (MB ≃ +5 like some old novae) or strong-lined (E.W. ≃ 60 Å) and faint (MB > 7 like dwarf novae).

Within globular clusters, stars of similar temperatures and gravities commonly exhibit differences in the strength of the λ3883 CN band, the distribution of which is often bimodal. An archetype example of this phenomenon is NGC 6752 (Norris et al. 1981). As documented by Da Costa and Cottrell (1980), and Norris et al. (1981), the CN-rich giants in this cluster possess enhancements in nitrogen abundance by factors of 7–8 relative to the CN-poor giants. This may indicate that chemical enrichment of proto-cluster gas clouds took place as a result of the activity of massive stars, which manufactured nitrogen within their interiors and ejected it into the cluster gas while low mass stars were forming. The aim of this paper is to investigate whether the properties of NGC 6752 mentioned above might be consistent with supernova enrichment. Both the free and adiabatic expansion phases of supernova shells (Spitzer 1968) will be discussed in this context.