Are the inner regions of the Galaxy younger, older or the same age as the outer halo? We have undertaken a study of globular clusters which lie within 4–5 kpc of the Galactic center. Here we present results for three of these clusters: NGC 6723, NGC 6352 and NGC 5927. We have constructed cluster color-magnitude diagrams from which we have determined their ages using the magnitude difference between the horizontal branch and main-sequence turnoff following the procedure of Carney, Storm & Jones (1992, CSJ). We find that 47 Tuc, NGC 6352 and NGC 6723 are coeval to within the errors, while NGC 5927 appears younger. The figure below is a reproduction of Figure 20 of CSJ with our clusters added.

Despite enormous effort put into the membership determination of M67, we do not know very well its peripheral members. Since the Bonn double astrograph as well as Pulkovo normal astrograph plates cover nearly 1°.5 × 1°.5 on the sky we have combined newly derived astrometric data from both instruments. Nearly 2,000 stars were measured down to the plate limit B ≈ 16.5. The proper–motion standard error for well-measured stars is ±0.3 mas/yr. For the membership probability solution we selected only 1363 stars, all brighter than V ≈ 15.0, with good proper motions. The membership solution yielded 446 cluster members showing convincing discrimination between the cluster and field stars. The spatial distribution of peripheral cluster members seems to be asymmetric, although, it does not indicate that the tidal radius of the cluster has been reached.

The Caspec échelle spectrograph at the ESO 3.6m telescope was used to obtain high resolution spectra for Arp 1145, and the star 2 of the metal-rich cluster Terzan 1. Arp 1145 was selected from Pickles & van der Kruit (1990). The star Tz1-2 was selected from Terzan 1 BVRI photometry carried out by Ortolani, Bica & Barbuy (1993) New HST CMDs show that Terzan 1 appears to be located nearby the Galactic center.

The central 2×3 arcmin2 region of M4 has been observed as part of a programme to find blue stragglers in globular clusters. A preliminary analysis has been carried out of 58 V frames and 65 I frames obtained on two separate occasions with an RCA CCD on the 1.0m telescope at Sutherland.

We reanalyzed the observational material of high resolution, high signal-to-noise spectra for a sample of 27 halo stars. The data were collected with the Coudé Echelle Spectrometer (CES) fed by the 1.4m Coudé Auxiliary Telescope (CAT) at the European Southern Observatory (La Silla, Chile). Data reduction are the same as described in a previous paper (Zhao and Magain, 1991). However, the non-linearity present in the data was corrected by using an empirical fitting formula (Gosset and Magain, 1993). The atmospheric parameters of these program stars have been determined. Effective temperatures were derived from b – y and V – K color indices by using the calibration of Magain. Surface gravities were determined by forcing the Fell lines to indicate the same abundance as the high excitation FeI lines. Metallicities were derived from Strömgren m1 indices. The abundances of a number of heavy elements, namely, strontium, yttrium, zirconium, barium, lanthanum, cerium and europium, are deduced on the basis of a new data reduction. The main results are: (1) The elements of the first peak, strontium–yttrium–zirconium, show the odd–even effect: strontium and zirconium are less deficient than yttrium in halo stars. (2) The yttrium abundance is constant for all stars with [Fe/H] > −2.5. (3) [Ba/Fe] values are 0.25 dex higher than solar for [Fe/H] > −1.8. (4) The barium overdeficiency increases with decreasing metallicity when [Fe/H] < – 1.8. (5) Lanthanum and cerium are overdeficient with respect to iron. (6) Europium is overabundant for −1.0 > [Fe/H] > −2.0.

Numerous blue halo stars have been discovered during the past decade (e.g. the Palomar-Green Survey). Many are horizontal branch type, being HBA, HBB, sdB, or sdO star. The sdB stars (Teff between ≈ 18 000 and ≈ 30 000 K) are the endproducts of evolution in the red-giant phase. This means that the spatial distribution of the sdB stars can be used to get insight in the population nature and in their spatial origin.

Zinn & Lee (1994, in prep.) have shown that the halo globular clusters with Rgc < 6 kpc are dominated by clusters with relatively blue horizontal branches for their metal abundance, which they interpret as a sign of their old relative ages. Of these “Old Halo” clusters having −1.7 < [Fe/H] < −0.8 dex, they find a net rotation about the galactic center of Vrot = 59 ± 22 km s−1, and a line-of-sight velocity dispersion of σlos = 62 ± 10 km s−1.

From measurements of Tautenburg Schmidt plates with the APM facility in Cambridge we obtained absolute proper motions of the Galactic globular clusters M 3 and M 92 directly with respect to large numbers of background galaxies (Scholz et al. 1993, 1994). We have extended our work to the dSphs in Draco and Ursa Minor (Scholz & Irwin 1994) and to other Galactic globular clusters using Tautenburg, Palomar and UK Schmidt plates. Combining our absolute proper motion of a cluster with its known radial velocity and distance (using common parameters of the solar motion) we derive the cluster orbit in the Galaxy (cf. Odenkirchen & Brosche 1992).

We have studied a sample of 26 globular clusters for which so far absolute proper motions exist in the literature. The proper motions were combined with distances and radial velocities for a determination of the space motion of the clusters. Using different galactic potentials (see Dauphole & Colin 1994 and references therein) we calculated the orbits of the globular clusters and their time averaged eccentricities, total energies, and apo- and perigalactic distances. The relation of the orbital quantities to the metallicities of the globular clusters has been studied. Preliminary results of this study were presented in Geffert et al. (1993).

We have investigated the V, B – V “clump” morphology of the globular cluster NGC 6553 (Ortolani et al. 1990, OBB90) through synthetic horizontal branch (SHB) models. Catelan's (1993) computations were extended to more metal-rich compositions, following Sweigart (1987) and Castellani et al. (1991), and transposed to the observational plane on the basis of VandenBerg's (1992) colour transformations and bolometric corrections. Observational scatter has also been added. In general, the SHB models are very clumpy, unlike the observed feature, which seems extended and peculiarly tilted. However, for particular combinations of helium abundance, metallicity, and mean mass on the HB, tilted models result, being however significantly less sloped and wider than observed. The NGC 6553 field is differentially reddened by ΔE(B – V) ≈ 0.06 (OBB90), which has been modelled, but which implies a CMD scatter which is smaller than the one originating from evolution away from the zero-age HB alone. We have also investigated the age of the cluster (ΔV method) and location of the red giant branch “bump,” in comparison with 47 Tuc. Since the helium and α-elements abundances are not known for NGC 6553, three chemical evolution scenarios have been considered, following the method of de Freitas Pacheco (1993). Details can be found elsewhere (Catelan et al. 1994).

Deep WFPC2 images in wide bands centered at 606 and 802 nm were taken with the HST 5.6 arcminutes from the center of the galactic globular cluster NGC 6397. The images were used to accurately position ~ 2120 stars detected in the field on a color magnitude diagram down to a limiting magnitude m814 ≃ mI ≃ 26 determined reliably and solely by counting statistics. A white dwarf sequence and a rich, narrow cluster main sequence are detected for the first time, the latter stretching from m814 = 18.5 to m814 = 24.0 where it becomes indistinguishable from the field population. Two changes of slope of the main sequence at m814 ≃ 20 and m814 ≃ 22.5 are evident. The corresponding luminosity function increases slowly from M814 ≃ 6.5 to 8.5 as expected from ground based observations but then drops sharply from there down to the measurement limit. The corresponding mass function obtained by using the only presently available mass-luminosity function for the cluster's metallicity rises to a plateau between ~ 0.25 and~ 0.15 M⊙, but drops towards the expected mass limit of the normal hydrogen burning main sequence at about 0.1 M⊙. This result is in clear contrast to that obtained from the ground and implies either a substantial modification of the cluster's initial mass function due to dynamical evolution in its lifetime, or that very low mass stars are not produced in any dynamically significant amount by clusters of this type. The white dwarf sequence is in reasonable agreement with a cooling sequence of models of mass 0.5 M⊙ at the canonical distance of NGC 6397 with a scatter that is most likely due to photometric errors, but may also reflect real differences in mass or chemical composition.

The principal aim of this work is to map the stellar distribution of a large sample of galactic globular clusters from the central regions to the outer envelope (beyond the tidal radius for an estimate of the foreground/background contamination) with a good statistical sampling of stars in the different branches of the color-magnitude diagram and with different masses. These new data will be used to investigate the dynamical evolution of stellar systems embedded in the gravitational field of our Galaxy, and, eventually, to set constraints on the mass distribution of the Milky Way. In this context, star counts have been carried out on V and I CCD frames of the rich, low concentration galactic globular cluster M55. The frames cover 35% of the cluster, from the center to 1.3 times the tidal radius (with total coverage inside 1rc). From V=14 (i.e. the horizontal branch level) to a limiting magnitude V=22 (MV = 7.9), a total of 36800 stars have been measured. A population of blue stragglers (BS) has been identified, but, at variance with other clusters of similar core concentration, the BS of M55 are only marginally more concentrated toward the center. No population gradient has been identified in M55. A luminosity function down to V = 21.3 has been obtained, after applying completeness and field star contamination correction to the star counts. The mass function is very flat (xglobal ≤ −0.5), as it was expected for this cluster located close to the galactic center and to the galactic disk. A single mass King model fitted to the radial star counts gives a core radius rc = 143″ and a tidal radius rt = 970″, ~ 10% greater than previously estimated.

Baade's Window (BW) has long been observed because of its low absorption and its position near the galactic centre. These characteristics permit the observation of many stars which are presumably members of the galactic bulge; although it is not possible to exclude contamination of this field by stars belonging to the galactic disc. Geometric arguments as well as galactic models allow to see that most of the stars are located far away from the solar neighbourhood. Based on this fact alone, many astronomers have assumed that the entire stellar population observed in BW consists of bulge stars.

A V, B- V composite colour-magnitude diagram, based upon CCD photometry from V~ 12 on the red giant branch to V~ 25 on the main-sequence has been derived for the globular cluster M4. A distance to the cluster of (m – M)v = 12.84 ± 0.19 is determined and the best match to theoretical isochrones is for the case [Fe/H]=−1.27 and an age of 16±1 Gyr. A differential age comparison with NGC 362 shows that M4 is approximately 1.7 Gyr older.

CCD observations have been carried on 4 fields in the outer disk and one in the halo of M31 on the 5m Hale telescope, and reduced using the Starman stellar photometry package (Penny, 1992). CMDs for all fields show the brightest 3 magnitudes of the Red Giant Branch. AGB luminosity functions were constructed for each field and corrected for incompletness. Full details are given in Morris et al (1994).

The Pegasus dwarf galaxy (DDO 216) is a resolved irregular galaxy. We present a study of stars in this galaxy based on BV RI CCD photometry obtained using the Palomar 1.5m telescope. The color-magnitude diagrams show (a) a dominant red giant branch (RGB) population, (b) a small number of asymptotic giant branch (AGB) population above the tip of the RGB (TRGB), and (c) a sparse popultion of massive young stars including the brightest red supergiants. The mean metallicity of the RGB has been estimated from the color of the RGB at MI = −3.5 mag: [Fe/H] = −1.5 ± 0.2 dex. The distance to this galaxy has been measured using the I-magnitude of the TRGB: (m – M)0 = 25.13 ± 0.11 mag (d = 1060 ± 50 kpc) (see Lee et al. 1993). This value is significantly smaller than the Cepheid distance estimate by Hoessel et al. (1990), (m – M)0 = 26.22±0.20 (d = 1750±160 kpc).

We have investigated the dynamical state of the disks of a set of 9 spiral galaxies fainter than MB = −18 and with Hubble types Scd or later for which rotation curves are available in the literature. The rotation curve of each galaxy is decomposed in disk and dark halo contributions in order to determine the mass distributions of both components. The velocity dispersion of dwarf spirals is not known, but we use the vertical scale heights of the disks assuming vertical hydrostatic equilibrium to derive estimates of the velocity dispersions. For this purpose we have performed a statistical flattening analysis of faint dwarf spirals in the ESO-Uppsala catalogue. We find that the intrinsic ratio of vertical to radial scalelengths of these types of galaxies is z0/h = 0.2 corresponding to an intrinsic flattening of q0 = 0.14.

The evolution of stars on the AGB has been explained as episodic helium burning and neutron capture nucleosynthesis in the stellar interior, followed by the mixing of a portion of the processed material into the envelope of a star. The simple stellar evolutionary scheme M–MS–S–SC–N had been accepted. However in recent years extensive observations of AGB stars have shown that evolution of the AGB is more complicated than painted in such a simple picture.

In order to extend the available abundance information in the Magellanic Clouds, and particularly the elemental ratios, we have undertaken a homogenous sudy of supergiants stars in both Clouds using high resolution spectroscopy. We compare the abundance ratios obtained for nine LMC F-supergiants (Hill et al., 1994) with those for three SMC similar stars (Spite et al., 1989).

The complex effects that determine the shape of an observed Colour Magnitude Diagram (CMD) are best disentangled through numerical simulation. We make synthetic CMDs by randomly extracting stars from theoretical stellar evolution tracks using a series of adopted initial conditions, including an Initial Mass Function. Utilizing reliable error estimates on our photometry provided by the program DoPHOT we apply a Maximum Likelihood technique to quantitatively determine which of the numerous different possible models is the most probable match to the data. From these comparisons we obtain a better understanding of how star formation proceeds in the relatively simple environments provided by Dwarf galaxies.