The way star cluster systems in galaxies are forming and survive seem to depend on the relation of the central density ρ (at half mass radius) of each cluster with its galactocentric distance Rgc. It is found that this relation takes the form of: The cluster systems of our Galaxy and of the two Magellanic Clouds, have been investigated. We have taken the cluster system of the conventional globulars of our Galaxy whereas the young and old systems of clusters in the LMC and SMC were treated separately. The radial distributions of central densities and half mass radii were found for all these systems showing a definite trend which depends on: (α) The total mass of the parent galaxy & (β) The age of the cluster system (young - old). It therefore appears that the total mass and/or the morphology of the parent galaxy plays a major role on the loci where clusters survive and form.

Preliminary results are presented for 3 southern globular clusters that have been searched via CCD photometry for new short-period variables that might be associated with blue stragglers. The clusters considered here are NGC6121, NGC3201 and NGC6809.

The morphological features of CMDs of Be 69 are better understood in terms of convective overshooting. The comparison of CMDs with the convective overshoot models (Bertelli et al. 1994) produces a good fit for a metallicity Z=0.008, age = 0.8 − 1.0 billion yr and (m-M) = 14.3, which corresponds to a distance of 2860 pc.

We present a color magnitude diagram (CMD) in the V and I bands reaching ∼ 4 magnitudes below the turn off (TO) for the galactic globular (?) cluster Pal 1. A comparison with other well-observed clusters and theoretical models suggests that Pal 1 has an age of 8±2 Gyrs, which would make it the youngest globular cluster of our Galaxy.

We present preliminary results of the analysis of a set of Hubble Space Telescope/Faint Object Camera images of the center of M15, the prototypical post-core-collapse globular cluster. We rule out, at the 95% confidence level, the 2″.2 core claimed to be detected in pre-repair HST imaging. We also measure a mass function in a field 20″ from the center.

Globular clusters (GC) of different galaxies are thought to be similar in their intrinsic nature, despite the very different environments in which they reside. This statement is mainly based on the luminosity function of GC that appear to be similar for galaxies structurally very different (Secker and Harris 1993). To support the above conclusion only few other GC parameters have been used: integrated colors and metallicity index (Harris 1991). Now, there is a growing body of GC velocity dispersions of other local group galaxies which can be used to perform a useful comparison. The tool for such a comparison is the correlation between GC total luminosity, Mv, and velocity dispersion, σ, found by Djorgovski (1991). This is one of the best non trivial correlation of GC structural parameters that can give important answers to the problems of the formation and evolution of GCs.

Although globular clusters are known to contain a population of neutron stars, the recent finding by Lyne and Lorimer (1994) that field neutron stars are formed with a mean “kick” velocity of 450 km s−1 implies that globular clusters would retain very few neutron stars. The number of neutron stars is important when discussing cluster mortality and the formation rate of millisecond pulsars.

Our recent HST/FOS spectra (Grindlay et al 1995; GC95) have spectro-scopically identified the 3 central Hα candidates (Cool et al 1995; CG95) as the probable cataclysmic variable (CV) counterparts of the the three central dim x-ray sources (Cool et al 1993; CG93) in the nearby core collapsed globular NGC 6397. Here we present the x-ray vs. optical properties of these three objects, derived from the FOS spectra presented in GC95 and the x-ray data of CG93, which strengthen the case that they are CVs and not quiescent LMXBs. Additional data and discussion are presented in the accompanying paper by Grindlay (these proceedings).

We compute the outcomes of close encounters between a binary and a single black holes including the effects of gravitational radiation reaction. All masses of individual black holes are assumed to be 1 M⊙. We found that merger of two black holes takes place during the encounters in some cases. Thus the gravitational radiation can act as a mechanism for the dissipation of energy of a cluster mainly composed of 10 M⊙ black holes which are produced by the evolution of high mass stars. The merger probability depends on many parameters in a complex way. Our preliminary calculations show that about 10% of the strong encounters (i.e., rp ∼ a) between a binary of hardness 100 and a single lead to mergers of two black holes in the stellar system of one-dimensional velocity σ = 100 km/s.

The number of compact stars such as white dwarfs, neutron stars, and black holes in globular clusters gives us information on binary formation rates and dynamical history of the clusters.

A significant depletion of red giants is observed in the central regions of post-collapsed globulars (Djorgovski et al., 1993) like M 15 (Stetson, 1991). A simple model shows that the depletion of red giants in the high-density cores of globular clusters can be understood in terms of mutual stellar collisions. Slightly outside the core stellar collisions are not frequent enough to explain the reduction in the observed number of red giants.

The bimodal nature of the horizontal branch (HB) of NGC 1851 is known since Stetson (1981). In order to better understand the properties of its HB, we collected a set of data at the ESO-NTT telescope, which provides a full coverage of the cluster area. Additional archive images from the HST-WFPC camera have been used in order to study the central region. The resulting c-m diagram (CMD) for 20500 stars is presented in Fig. 1 (left). Despite its metallicity ([Fe/H]=−1.3), NGC 1851 presents a well defined blue HB tail, besides the expected red clump. The observed CMD has been compared with the synthetic ones. The bimodal HB can be reproduced assuming that there are two stellar populations in the cluster, with an age difference of ∼ 4 Gyr, hypothesis not supported by other properties of the CMD. On the other side, if we assume that the stars in NGC 1851 are 15 Gyr old (as suggested by the difference between the HB and the TO luminosities), only a bimodal mass loss can reproduce the HB morphology: only stars with higher than standard mass loss rate are able to populate the blue-HB (BHB) tail (Fig. 1,left). There are no observational evidences for a bimodal distribution of other parameters (He, CNO, etc.).

Although many projects were aimed at identifying nearby red dwarfs, the catalogues may be complete up to a limiting distance of 5 pc only and may be reliable to 10 pc. From recent observations it is evident that their absolute visual brightness (MV) ranges from about 6 to at least 18.5 what means that an average dK0 star is at least 100,000 times brighter than red dwarfs of the latest spectral subclasses. The photon detecting efficiency of our instruments is to be increased that these can measure late dM stars from the same distance from which dK stars can be analysed now. Another solution is offered by the flare-active red dwarfs which may be 1000 times brighter during their flare ups than usually.

The kinematics of the binary systems to which supernovae(SNe) 1993J and 1994I belonged are studied. The kick velocity caused by supernova(SN) asymmetry will highly influence the fate of the system. The survival rates with assumed kick velocity distribution are discussed.

Observations of Globular Cluster ellipticity distributions related to some fundamental parameters give strong evidence for a decay of rotational energy in these systems with time. In order to study the effectiveness of angular momentum transport (or loss, resp.) a code has been written which solves the Fokker-Planck equation in (E, Jz)-space and follows the evolution from some initial conditions through core collapse (and possibly gravothermal oscillations) up to the post-collapse phase. For the purpose of comparability with N-body simulations rotating initial model configurations according to the prescriptions of Lupton & Gunn (1987) have been constructed. These models are intended to continue previous work by Goodman (1983, Fokker-Planck) and Akiyama & Sugimoto (1989, N-Body). In this contribution the derivation of the flux coefficients is given.

We investigated collisionless aspects of the early evolution of model star clusters. The effects of mass loss through stellar evolution and of a steady tidal field are modelled using N-body simulations. Our results (which depend on the assumed initial structure and the mass spectrum) agree qualitatively with those of Chernoff & Weinberg (1990), who used a Fokker-Planck model with a spherically symmetric tidal cutoff. For those systems which are disrupted, the lifetime to disruption generally exceeds that found by Chernoff & Weinberg, sometimes by as much as an order of magnitude.

In this paper, we show a new algorithm to integrate the orbits of binaries. Our new algorithm has the good properties of both symmetrized timesteps and KS regularization: (1) no secular error in either energy or angular momentum; (2) a constant number of timesteps per orbit for a binary with arbitrary eccentricity (Funato et al., 1995).

This paper describes a numerical method for following the evolution of the orbit of a perturbed binary (e.g. the inner binary of a hierarchical triple) by means of averaging.

We present results on the exchange cross section for the interaction between a hard binary and a field of single stars, for arbitrary masses. The results are based partly on extensive numerical scattering experiments, and partly on analytic estimates of the mass-dependence of the cross section. They can be used to estimate the rate of exchange in an arbitrary mixture of masses, provided that the binary is hard.

Since Lucy and Gingold & Monaghan invented smoothed particle hydrodynamics (SPH), it has been used to study a variety of astrophysical problems. A broad discussion of the method can be found in a review by Monaghan. However, the most serious disadvantage of SPH remains to be overcome: it cannot handle strong shocks accurately. Especially in three dimensional calculation, particles often penetrate each other, and there are typically large post-shock oscillations.