High resolution échelle spectra were obtained with the FEROS spectrograph at the 1.5m ESO telescope for 35 nearby bulge-like stars. From Hipparcos data it appears that the turn-off of this population indicates an age of 10–11 Gyr (Grenon 2000).

Oxygen abundances are calculated using the [O I] line at 6300.3 Å. The derived results show an oxygen overabundance for most of our sample stars when compared to their disk counterparts.

We present a study of the star cluster associated with the massive Galactic HII region NGC 3603 based on near-IR broad- and narrowband observations taken with ISAAC/VLT under excellent seeing conditions (≤ 0.4″). We discuss color-color diagrams and address the impact of the high UV flux on the disk evolution of the low-mass stars.

We have imaged over an extensive field the 3.29-μm emission from the Carina Nebula. This emission arises from polycyclic aromatic hydrocarbons which are excellent tracers of photodissociation regions. The results emphasis the two very different environments of the massive star clusters of the nebula, Trumpler 14 and 16.

The Arches cluster - located only 11′ from the Galactic Center (GC) - is one of the densest and richest young star clusters in the Milky Way. With an age of only about 2 Myr, it is ideally suited to study massive cluster formation in an extreme environment. We find an IMF slope of Γ = −0.77 from 5 to 100 M⊙, in good agreement with the results from HST/NICMOS from Figer et al. (1999). The limiting factor in the dense cluster center is crowding. With the new AO systems, high resolution analysis of the dense cluster region combined with very deep infrared photometry is available. We have analysed deep H and K′ images of the cluster center obtained with the GEMINI/Hokupa'a adaptive optics system. Colour-magnitude diagrams and the IMF are constructed from these data. A comparison with isochrones yields the mass function.

Asteroseismology of multiperiodic δ Scuti stars is a powerful tool for providing estimates of distances to the stars being analyzed. Especially δ Scuti stars in clusters offer good possibilities for determining asteroseismic distances, as the stellar models are constrained by assuming common values for chemical composition, age and distance. Recently, we detected a large population of δ Scuti stars in the open cluster NGC 7062. On the basis of these results, we discuss the potential of extending the asteroseismic distance scale for δ Scuti stars to include extra-galactic stellar clusters. Especially high-amplitude δ Scuti stars, pulsating in at least 2 radial modes, offer promising possibilities for doing this.

The complicated star formation history of the most massive globular cluster in our Galaxy — ω Centauri — is seen as a presence of an asymmetric spatial distribution of two stellar populations having different ages and metallicities. The cluster hosts the largest known sample of Population II δ Sct variables, or SX Phœnicis stars, which are valuable Galactic and extragalactic distance estimators. We discuss the applicability of these variables for estimating distances to the cluster, and compare different techniques for the critical identifications of oscillation modes.

We report new, as yet unpublished HST/WFPC2 V, I photometry of 9 globular clusters in M31. These are part of a total sample of 19 clusters on M31 with well observed CMDs from HST. The clusters have the full range of horizontal branch morphologies from blue HB to red clump, but none are found with an extreme (blue only) horizontal branch. Plots of HB type vs [Fe/H] are similar to those of Galactic clusters, including a hint of second parameter clusters. Sixteen halo fields adjacent to the observed clusters included in our images have been analysed. The M31 halo metallicity distribution peaks at [Fe/H]=-0.7 dex with a tail toward low metallicity, resembling the halo of NGC 5128; metal-rich giants appear to be centrally concentrated.

We present a progress report on Washington photometry of several hundred new globular cluster (GC) candidates in M31 which were recently found from our new CCD survey of GCs. The Washington CMT1 filters that we used are very efficient to survey extragalactic GCs and to estimate the metallicity of GCs. Preliminary color-magnitude diagrams and color-color diagrams of the new GC candidates and known GCs in M31 are obtained.

Searching for globular cluster candidates in nearby galaxies such as M31 is the first step to study the characteristics of extragalactic globular cluster systems. Previous searches for M31 globular clusters were mostly based on visual inspection of photograpic plates. We have selected globular cluster candidates from a wide-field Washington CCD survey of M31, using various methods: color-magnitude diagrams, color-color diagrams, point spread function subtraction and visual inspection of the objects. The efficiency and accuracy of these methods for finding globular clusters are presented.

We present a new method for finding associations of young stars in M31 using broadband WFPC2 data from the HST data archive. Applying our identification method to 13 WFPC2 fields, covering an area of ∼60 arcmin2, has revealed 80 new candidate young star clusters in these portions of the M31 disk. Most of these clusters are small (≳5 pc) young (∼10–200 Myr) star groups located within large OB associations. We have estimated the reddening values and the ages of each candidate individually by fitting isochrones to the stellar photometry. We provide a catalogue of the candidates including rough approximations of their reddenings and ages.

We have observed the M31 globular clusters with the University of Hawaii Adaptive Optics System Hokupa'a at the Gemini North 8m telescope on Mauna Kea. This is part of a project which aims at spatially resolving intermediate-age and old-age stellar populations in the Local Volume and beyond - possibly out to distances of the Virgo and Fornax clusters. The sparse M31 globular cluster G27 (Hubble 6) is for the first time resolved into individual stars. The tip of the red giant branch (TRGB) at K≈18.8mag yields a metallicity of Z around 0.001 solar for G27.

We have obtained HST-NICMOS observations of five of M31's most metal-rich globular clusters: G1, G170, G174, G177 & G280. For the two clusters farthest from the nucleus, G1 and G280, we statistically subtract the field population and estimate metallicities using K-(J - K) color-magnitude diagrams (CMDs). Based on the slopes of their infrared giant branches we estimate [Fe/H] = −1.22 ± 0.43 dex for G1 and −0.15 ± 0.37 dex for G280. We combine our infrared observations of G1 with two epochs of optical HST-WFPC2 F-band data and identify at least one LPV based on color and variability. The location of G1's giant branch in the K, (V - K) CMD is very similar to that of M107, indicating a somewhat higher metallicity than our purely infrared CMD; [Fe/H]= −0.9 ± 0.2 dex.

We present a photometric study of the stars in ionizing star clusters embedded in several giant H II regions of M33 (CC93, IC 142, NGC 595, MA2, NGC 604 and NGC 588). Our photometry is based on the HST-WFPC2 images of these clusters. Color-magnitude diagrams and color-color diagrams of these clusters are obtained and are used for estimating the reddenings and ages of the clusters. The luminosity functions (LFs) and initial mass functions (IMFs) of the massive stars in these clusters are also derived. The slopes of the IMFs range from Γ = −0.5 to −2.1. Interestingly, it is found that the IMFs get steeper with increasing galactocentric distance and with decreasing [O/H] abundance.

We analyse star cluster properties in the nearby spiral galaxy M33, combining our extensive HST WFPC2 photometry and ground-based follow up spectroscopy. These data show that cluster velocity dispersion increases with age. Simulations comparing synthetic disk and halo populations with observations indicate a composite disk/halo system for the old M33 clusters. The best fit fraction of 85 ± 5% halo plus 15 ± 5% disk differs from that found in the Milky Way, where ∼ 30% of the globular clusters are metal rich objects associated with the bulge and/or thick disk. Spectroscopic line indices for a halo subsample (17 objects) reveal an age spread of ∼ 5 — 7 Gyr, and little progression in metal abundance with age. This is consistent with a chaotic formation for a substantial portion of the M33 halo, and also consistent with an accretion origin for a large number of the halo clusters.

I suggest that the bulk of the “young”, second-parameter globular clusters (SPGCs) observed in the outer halo of our Galaxy and recently found in the other massive spiral of the Local Group (LG), M33, may have originated due to mass outflow from M31 and subsequent accretion of gas on the Galaxy and M33 in the early epoch.

We present deep V, I photometry of the globular cluster Terzan 7, a probable member of the globular cluster system of the Sagittarius dwarf spheroidal galaxy. The metallicity, estimated from a new method based on analytic RGB fits, agrees with previous estimates based on color-magnitude diagrams ([Fe/H]= −0.9 ± 0.1 dex). This result confirms a discrepancy between photometric and spectroscopic determinations. Using both the horizontal and vertical methods to estimate relative ages, we confirm that the age of Terzan 7 is about 70% that of 47 Tuc. A rich population of blue stragglers is found, strongly concentrated toward the center of the cluster.

We report on new B, V and I CCD photometry of the globular cluster M54 that was aimed at the study of its variable stars. With respect to the previous most recent work on M54 we have nearly doubled the number of detected variable stars: M54 can now be classified as intermediate in the Oosterhoff groups. The metallicity can be estimated for the cluster and field red giant stellar population, and for the variables.

Using VLT UVES spectra of resolving power near 23,000 we have analyzed three stars in Terzan 7, a globular cluster associated with the Sagittarius Galaxy. We find [Fe/H] = −0.61±0.1, [O/Fe] = +0.25, [α/Fe] = +0.23 dex, and an enhancement of r/s elements as compared with the Sun and Arcturus.

We present the surface photometry of star clusters in the nearby dwarf elliptical galaxies NGC 185 and NGC 205, obtained from deep HST WFPC2 F555W (V) and F814W (I) images. We have obtained surface brightness and color profiles of six star clusters in NGC 185, seven star clusters in NGC 205, and one recently discovered non-stellar object in NGC 205. The surface brightness profiles of ten star clusters are fitted well by the King model, and those of four star clusters are fitted well by the power-law. Three out of ten star clusters fitted well with King model show signs of tidal tails.

V and I images of the nearby dIrr galaxies Sextans A and Sextans B were searched for star clusters. The candidates were selected, from a sample of non-stellar objects, on the basis of their morphology, their integrated colors and magnitudes. One of the candidates in Sextans A shows a few resolved stars whose location in the color-magnitude diagram indicates the cluster is at least older than 1 Gyr.