The distances to old stellar populations have traditionally been derived from three standard candles: the luminosity of the red-giant-branch tip, the absolute magnitudes of RR Lyrae stars, and the colour–magnitude-diagram loci of nearby subdwarfs. The distance-modulus uncertainties that are associated with these methods are still at the level of ±0.10–0.15 mag. Current stellar models are able to satisfy these age-independent constraints to well within their error bars, which are mainly owing to the uncertainties in the distances of the calibrating objects and, directly or indirectly, to chemical-abundance uncertainties. The impact of varying the physics and the assumed abundances in stellar models on the aforementioned standard candles is discussed, as is the use of the giant-branch bump luminosity to constrain the distance scale.

The primary goal of the sacy project (Search for Associations Containing Young Stars) was to identify possible associations of stars younger than the Pleiades association among optical counterparts of ROSAT X-ray-bright sources. The study of the chemical abundance in stars located in regions of stellar formation is extremely important to understand stellar nucleo-synthesis, the physical mechanisms controlling mixing in stellar interiors, and chemical enrichment in the Galaxy. The present work highights the first results of a chemical-abundance study of evolved stars identified in the sacy survey. For this, we performed a detailed spectroscopic analysis for the determination of atmospheric parameters and Li abundance for a sample of giant and subgiant stars. The observations were carried out with high resolution using the FEROS (R = 48 000) échelle spectrograph. We measured the stellar parameters (Teff, log g, vmic, [Fe/H]) from LTE analysis in the complete range of 420-1100 nm. Li abundance was derived from the region around the lithium line at 6707.78 Å for the entire sample of stars.

A few star clusters in the Magellanic Clouds exhibit composite structures in the red-clump region of their colour–magnitude diagrams. The most striking case is NGC 419 in the Small Magellanic Cloud (SMC), where the red clump is composed of a main blob as well as a distinct secondary feature. This structure is demonstrated to be real and corresponds to the simultaneous presence of stars which passed through electron degeneracy after central-hydrogen exhaustion and those that did not. This rare occurrence in a single cluster allows us to set stringent constraints on its age and on the efficiency of convective-core overshooting during main-sequence evolution. We present a more detailed analysis of NGC 419, together with a first look at other populous Large Magellanic Cloud clusters which are apparently in the same phase: NGC 1751, NGC 1783, NGC 1806, NGC 1846, NGC 1852 and NGC 1917. We also compare these Magellanic Cloud cases with their Galactic counterparts, NGC 752 and NGC 7789. We emphasise the extraordinary potential of these clusters as absolute calibration marks on the age scale of stellar populations.

I present results of a search for cataclysmic variables (CVs) and chromospherically active binaries (ABs) as counterparts to X-ray sources detected with Chandra in six Galactic globular clusters (GCs): M 4, M 28, M 30, M 71, M 80, and NGC 6752. Binary systems play a critical role in the evolution of GCs, serving as an internal energy source countering the tendency of GC cores to collapse. Theoretical studies predict dozens of CVs in the cores of some GCs (e.g., 130 for M 28, 40 for M 30). A number of such binaries are also expected outside the core radius. However, few CVs are known so far in GCs. Using the 4.1m SOAR telescope, I have found 25 stars with Hα excess in the observed clusters. Six are candidate CVs, five are candidate active binaries. The other 14 objects with Hα excess are probably foreground/background stars or extragalactic sources.

Open clusters have long been recognized as important objects to investigate aspects of Galactic structure such as the location of spiral arms, Galactic dynamics or even the chemical-abundance gradients in the Galactic disk. Great effort has been dedicated to studies of these objects throughout the past few years to determine parameters like age, distance, reddening, metallicity as well as kinematic information in a systematic and consistent manner. In this work, we present results on several open clusters selected from the DAML02 catalog that have been observed and investigated for the first time. CCD UBVRI (Johnsons–Cousins system) observations were carried out in 2009 using the 60 cm telescope of the Pico dos Dias Observatory (LNA/Brazil). The color–color and color–magnitude diagrams were analyzed for each cluster with the help of a program written by our group, which allows handling photometric and astrometric data simultaneously. We determined the fundamental parameters (reddening, distance and age) using the main-sequence fitting method, taking into account kinematic information of individual stars in the clusters. The mean proper motion and radial velocity were estimated using a set of stars selected photometrically.

The properties of the binary components of the eclipsing variables found in the 47 Tuc core region as part of a search for extrasolar planets have been re-examined following reanalysis of the image photometry and calibration. This is part of an ongoing study to find fundamental properties of stars of different metallicity in a variety of environments through eclipsing-binary analyses.

A review is given of the topics discussed during IAU Symposium 266 on star clusters, and of the major results presented. The current state of the art is discussed, together with potential prospects which may help to direct and generate future advances.

The three young, massive star clusters found in the Galactic Centre region (Young Nuclear Cluster, the Arches and Quintuplet clusters) are among the six most massive star clusters in our Galaxy, with masses similar to low-mass, extragalactic starburst clusters. The conditions for star formation in this region are extreme and likely comparable to those found in the Hii regions in starburst galaxies and tidal-interaction zones of mergers. As the inner Galactic star clusters can be resolved, they can serve as templates for extragalactic starburst clusters. With knowledge of the spectral types, masses and ages of the individual stars, their stellar population can be studied in detail, allowing derivation of their present-day mass function (PDMF). The Quintuplet cluster, with an age of about 4 Myr, is the most extended of the three clusters and also displays a lower spatial density. To determine its mass function correctly, the distinction between cluster and field stars is therefore of particular importance. We present the first determination of a proper-motion-membership sample for the Quintuplet cluster. By comparing two high-precision astrometric VLT/NACO data sets with a time baseline of 5 years, the displacement of the Quintuplet cluster relative to the field population was measured and a selection of the proper-motion cluster members could be established, from which the PDMF can be derived.

Starburst clusters are spectacular young and dense stellar systems containing copious numbers of massive O-type and Wolf–Rayet stars. These objects depict a stellar population comprising stars over the entire mass range, making them ideal objects to study cluster formation and evolution as well as to test and calibrate stellar evolutionary models. Among the Galactic spiral-arm starburst clusters, NGC 3603 Young Cluster (YC), which is located in the Carina spiral arm, is the youngest and most compact one. Galactic starburst clusters also serve as templates for extragalactic super star clusters as observed, e.g., in the Antennae galaxies. Based on two epochs (obtained 10 yr apart) of high-quality astrometric HST/WFPC2 observations, we derive individual proper motions for several hundred stars. The proper motions enable us to distinguish cluster members from field stars, and to derive a first estimate of the internal cluster dynamics. Photometry of the clean sample of cluster stars allows us to create color–magnitude diagrams (CMDs) that are not contaminated by field stars, and to compare the sequence of cluster members with different sets of theoretical isochrones and evolutionary tracks. We clearly identify a lower-mass pre-main-sequence and a higher-mass main-sequence stellar population in NGC 3603. A particular focus of our comparison with theoretical isochrones is the exact shape and extent of the pre-main-sequence/main-sequence transition region in NGC 3603 YC. The proper motions also contain dynamical information. From this, we derive a velocity dispersion, which leads to the first dynamical mass estimate of the NGC 3603 cluster. We also investigate whether or not NGC 3603 YC is virialized, and study evidence for primordial versus dynamical mass segregation. Past and future evolution of NGC 3603 YC can be studied and will tell us about the clusters ‘fate’ and its long-term survival chances.

We constructed a program that allows one to use simultaneously and interactively photometric and astrometric stellar data (proper motion) to analyse color–color and color–magnitude diagrams. With this program, we are able to determine, based on photometric membership, the distance and age as well as the mean proper motion and radial velocity of several open clusters which had very uncertain parameters in previous analyses.

We present BV photometry and the results of a search for stellar variability in the Galactic globular cluster M 69. The resulting color–magnitude diagram shows significant contamination by field stars. In our variability search we found 62 variable stars, 54 of which were new discoveries.

Globular clusters have long been considered the closest approximation to a physicist's laboratory in astrophysics, and as such a near-ideal laboratory for (low-mass) stellar evolution. However, recent observations have cast a shadow on this long-standing paradigm, suggesting the presence of multiple populations with widely different abundance patterns, and—crucially– with widely different helium abundances as well. In this review we discuss which features of the Hertzsprung–Russel diagram may be used as helium-abundance indicators, and present an overview of available constraints on the helium abundance in globular clusters.