The possible existence of binary clusters in our Galaxy (h and x Persei, Ocl 556) has been argued in the past, but it has never been a well established fact either in our Galaxy, or in external systems. An early speculation on the problem by Innanen et al (1972) has predicted a considerable degree of stability for binary clusters in low nuclear density galaxies, like the LMC.

A program of investigation of globular clusters' structural parameters in nearby galaxies has been initiated at the Rozhen National Observatory, Bulgaria (Spassova and Staneva 1984). Here we report on the projected ellipticities of 88 bright globular clusters in M 31, obtained on plates taken with the 2 m Ritchey-Chretien telescope at Rozhen (16 m focal length, 12″89/mm plate scale over a 1° × 1° field).

Several dynamical theories have been developed in order to approach the dynamical evolution of stellar systems and explain the observational data. The observed density profiles of the clusters can be a valuable source of information towards the understanding of their dynamical properties. King in a series of papers has connected the established theories with the observed profiles in clusters of our own Galaxy (King, 1962, 1966; etc.). Density profiles can be obtained by means of star counts and/or by means of photometric photometry. So far the observations for clusters in our Galaxy and the MCs appear to fit well the so called King models and provide information of their tidal radii, total masses and concentration parameters (Kontizas, 1984).

Spectral classification of stars in SMC clusters provide useful information on the evolutionary history of this galaxy and permit us to test the theory of stellar evolution.

This small cluster is situated in the western region of the SMC at α = 0h 26m 13s, ε = −73°, 1′, 20″ (1950) and has been chosen for study in the initial post-launch period of the Hubble Space Telescope. This preliminary study was made using data obtained using a CCD camera on the SAAO 1 m telescope in October 1984.

We present Washington system photoelectric photometry for stars in three young LMC clusters: NGC 1850, NGC 1866, and NGC 2164. We derive metal abundances [A/H] of −0.3, −0.4, and −0.6, respectively.

A new technique for determining accurate abundances in distant giants - Washington CCD photometry - has been applied to the intermediate-age LMC globular cluster NGC 2213. An abundance of −0.40 ± 0.15 was found from the analysis of 42 giants with V < 20, using data obtained with the 1.5 m telescope. Combined with published main-sequence photometry, the derived abundance indicates a true LMC distance modulus of 18.2 ± 0.2. A likely CN strong giant near the tip of the giant branch is identified. Abundances are also derived for a sample of 27 field giants. Results indicate that one could determine both the age and abundance of Magellanic Cloud clusters with high accuracy from Washington photometry using the 4 m in less than one hour of observing time per cluster.

We report the results of deep CCD photometry of two overlapping fields in the Draco dwarf spheroidal galaxy. We find (B-V)o,g = m0.69, indicating a mean [Fe/H] = −2.0. The width of the giant branch below the horizontal branch is somewhat wider than our observational errors permit, from which we infer there is a spread in metallicities amongst the Draco giants, up to 0.8 dex, perhaps. Draco is found to contain numerous blue stragglers, like almost all other loosely bound halo systems. The number of such stars more massive than about 1.2 M⊙ is roughly consistent with the number of anomalous cepheids discovered previously. It is not clear whether the blue stragglers represent a large number of mass transfer binaries or an intermediate age population, or both. A younger population component would help explain the galaxy's red horizontal branch stars in spite of its low mean metallicity. Signs of a younger population are seen in the color magnitude diagram for the entire sample, and especially from the higher quality data from the smaller area observed in the overlap of the two fields.

The present study is concerned with the examination of properties of stars in the core of the Fornax dwarf spheroidal galaxy. Previous studies have shown that Fornax has a very diverse stellar population. Four of the globular clusters associated with Fornax were found to have metallicities significantly lower than the mean metallicity of the field population of the galaxy (Buonanno et al. 1985); these clusters point out an older, metal-poor population. Also, there are a number of luminous carbon stars, which are indicative of a much younger population (see Mould and Aaronson 1986). Studies of the field population of Fornax (Demers, Kunkel, and Hardy, 1979; Buonanno et al., 1985) have shown a dispersion in metallicity. We have measured a large sample of giant branch stars, enabling a good determination of mean properties of the Fornax stellar population, as well as allowing a comparison of stars as a function of distance from the center of Fornax.

Although close binaries are believed to be of importance in the dynamical evolution of globular clusters, searches for such binaries have produced mostly negative results, aside from x-ray sources. Two dwarf novae which are possible cluster members are known (Margon and Downes 1983) and two classical nova candidates have been found. The crowded field around the nova observed in 1860 close to the center of M80 makes ground-based recovery of that star impossible with present techniques. Here we report on our attempt to recover the star which erupted in 1938 about 30″ (0.8 core radii) from the center of M14.

We have taken UBVRI photoelectric photometry and CORAVEL radial velocities for 6 field RR Lyraes, i.e. SW And, YZ Cap, SW Dra, SS For, RV Phe and V440 Sgr, with the purpose of applying the Baade-Wesselink (B-W) method and determining their absolute magnitudes. The present improvements with respect to previous applications of the method are: a) the use of the (V-I) color, which shows the smallest sensitivity to gravity and metal abundance in the color-visual surface brightness plane. b) the use of a new grid of model atmospheres by Buser and Kurucz (1986), which include an improved treatment of opacity and convection. They provide a complete set of models for the relevant values of effective temperatures, gravities and metal abundances, thus avoiding the need of inaccurate interpolations or extrapolations.

Of all the different methods employed to estimate the mean absolute magnitude of RR Lyrae variables, only an analysis of the Baade-Wesselink type can determine this quantity directly. The distance to a globular cluster can therefore be measured by determining <MV>RR for that cluster instead of being forced to assume that <MV>RR is the same as that of the nearby field variables. This is important in that the field stars may have a different luminosity than cluster variables. In addition, since <MV>RR should depend on the composition (especially helium) and history of mass loss of these stars, this quantity may vary from cluster to cluster.

Thirteen double-mode RR Lyrae (RRd) stars, with mean magnitudes c = 18.30 ± 0.10 and <V>c = 17.80 ± 0.15, have been identified in the variable-rich Oosterhoff type I globular cluster IC 4499. The stars have surprisingly uniform properties, and are considerably different from RRd stars found in Oo II systems. The mean first-overtone period (Fig.1) is <P1>=0.357d ± 0.005d (cf. <P1>=0.40d for Oo II RRd stars), and the mean ratio of the first-overtone period to the fundamental period is <P1/P0>= 0.7443 ± 0.0002. The mean double-mode pulsation mass for the 13 stars, using the King Ia (Y=0.279, Z=0.001) mass calibration, is 0.535 ± 0.003 M⊙. Such an average mass is 0.11 M⊙ smaller (i.e. ~17% smaller) than that for RRd stars found in Oo II systems, and possibly ~0.01 M⊙smaller than the mean mass for the two RRd stars in M3 (it is important to note that the zero point of these mass determinations is uncertain by at least 15%). The metal abundances for the RRd stars, and for the system of RR Lyrae stars as a whole, are found to be consistent with <[Fe/H]>=-1.38 ± 0.20, determined from δS spectroscopy. In the Peterson diagram (Fig.2), all known RRd stars now divide (apparently by mass) into two groups (split according to Oosterhoff type). With a reddening of EB-V=0.26 ± 0.03, the cluster distance modulus is (m-M)o=16.23m ± 0.23m.

Three Galactic globular clusters of moderate metallicity, (−0.7 > [Fe/H] > −0.9), have been searched for variable stars. NGC 6388 and NGC 6569 appear to contain RR Lyrae variables as members; NGC 6652 does not. NGC 6388 and NGC 6569 thus appear to have bluer horizontal branches than normally found at their metallicity.

It came as a great surprise that many dwarf elliptical galaxies of very low surface brightness in the Virgo Cluster have conspicuous bright star-like nuclei (Reaves 1983, Binggeli, Sandage and Tammann 1985). These nuclei are at least a factor of 10 more luminous than the brightest globular clusters in the Local Group and comparable only to the very brightest globulars surrounding M87. They contain a considerable fraction (1 to 20%) of the total light of the parent galaxy (Binggeli, priv. commun.). Their physical nature and origin are a matter of debate (Zinnecker et al. 1985, van den Bergh 1985, Norman 1986, Zinnecker 1986) but optical spectroscopy for 3 objects indicates a stellar composition with a range similar to globular clusters (Bothun et al. 1985). It has been suggested that a central nucleus is formed when off-center bound star clusters migrate to the center as a consequence of dynamical friction (Norman 1986). Support for such a scenario comes from CCD observations of IC 3475 which reveal numerous knots near the center of this dwarf irregular galaxy (Vigroux et al. 1986). These knots have the same color as the parent galaxy and are interpreted as intermediate age star clusters.

Long exposures with the 4-Shooter at the Cassegrain focus of the 200-inch telescope at Palomar Observatory have been obtained for M87 (and two other giant ellipticals in Virgo). Ellipse fitting with a code specially developed to reject point sources has been carried out to determine the surface brightness in various bandpasses of the underlying galaxy. The color gradients in the galaxy are quite small over the entire regime between 2 and 350 arc-sec from the nucleus of M87. Also I find that there is no difference between the ellipse parameters (position angle and eccentricity) derived in the various colors, i.e. the isochromes and the isophotes coincide. Details of the study of the halo of M87 are described in a paper submitted to the Astronomical Journal.

We have observed the central distribution of globular clusters in M 87. The core radius of the cluster system is an order of magnitude larger than that of the underlying galaxy.

We present a photometric (U band) investigation of the globular clusters in the central region of M87 from deep calibrated photographic and electronographic material, obtained with the CFH telescope. The aim of this work is to complete previous photometric studies at longer wavelengths (Grillmair et al., 1986; Lauer and Kormendy, 1986).

We have used the Canada-France-Hawaii Telescope on Mauna Kea to obtain two deep CCD exposures in the central region of the Coma cluster, and we have used the new images to detect globular clusters in the central giant galaxy NGC 4874. One exposure with a total integration time of 2 hours lies in the halo of the giant galaxy. A second (comparison) exposure of the same integration time was taken within the cluster core but well away from any other bright galaxy. Our analysis, which includes both photometry and image classification with the automated routines called FOCAS, extends to a limiting B magnitude of 26.25. Image classification is a necessary part of this study because at the faintest limiting magnitudes globular clusters are easily confused with the rich population of faint background galaxies. We have been particularly successful in sorting stellar objects from galaxies because the image quality on our images is quite good: FWHM ~ 0.6 arcsec. The data were taken with the fast autoguiding instrument called ISIS (Thompson and Ryerson 1984)