The modern generation of electronic detectors, such as the CCD, have made improved photometry possible, especially at magnitudes near photographic plate limits and at wavelengths extending to the near infrared. Vigorous efforts should now be made to extend measurements to longer wavelengths since VandenBerg and Bell (1985) have recently calculated BVRI synthetic isochrones. Consequently, we have embarked on a program of CCD BVRI photometry for determining the ages of globular clusters.
From BVRI CCD frames obtained with the 1.54 Danish telescope at ESO-La Silla we have at this moment completed the reductions of the following 5 globular clusters: NGC 104 (47 Tuc), NGC 2298, NGC 5139 ( 0) Cen), NGC 6121 (M4), and NGC 6362. For these clusters, we have derived ages all close to 17x10^0y. Providing strong evidence that the globular cluster system is coeval, and that the epoch of the galactic contraction was short.
The influence of binaries on the evolution of globular clusters is studied numerically using the Monte Carlo method. It is assumed that initially the stellar systems are composed of single stars only and binaries are born /as a result of three-body encounters/ during the evolution of the clusters. The life of each hard binary in the cluster is studied individually. It is shown that the first binaries appear long before core collapse is completed, and then a population of a few hard binaries remains in the cluster during its whole life. Practically all energetic binary-single star interactions take place in the deep, internal parts of the core, populated mostly by the heaviest stars of the cluster. The binary-single star interactions become a source of energy which stops the collapse of the core and causes expansion and gradual disintegration of the whole cluster during the post-collapse phase.
Preliminary results of observations of 11 globular clusters made with the aid of a narrow long slit are presented. The photometric profiles were recorded directly in the operational store of a computer with the telescope stopped om iits motion about the polar axis. The photometric profile obtained were compared with King´s models and with the generalized sychrone model. The finite length and width of the slit were considered. The theoretical brightness distribution agrees well with observation in the central regions of the clusters at R < 3´- 5´. The radii of cores Rc and the effective radii Re were determined. Large-scale fluctuations of density, possible caused by bright stars, or by fluctuations of the abundant galactic background, were observed in clusters M12, M13 and NGC 6712.
The evolution of globular clusters under dissipation and dynamical friction is considered. It is shown that a gravothermal catastrophe in the cluster core appears before the cluster will be completely destroyed under dissipation, or will fall into the Galactic centre under dynamical friction. The objects which are formed in the cluster-core contraction process /massive black holes of close binaries/ also fall into the centre of the Galaxy, or populate its bulge.