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We present orbit analysis for a sample of eight inner bulge globular clusters, together with one reference halo object. We used proper motion values derived from long time base CCD data. Orbits are integrated in both an axisymmetric model and a model including the Galactic bar potential. The inclusion of the bar proved to be essential for the description of the dynamical behaviour of the clusters. We use the Monte Carlo scheme to construct the initial conditions for each cluster, taking into account the uncertainties in the kinematical data and distances. The sample clusters show typically maximum height to the Galactic plane below 1.5 kpc, and develop rather eccentric orbits. Seven of the bulge sample clusters share the orbital properties of the bar/bulge, having perigalactic and apogalatic distances, and maximum vertical excursion from the Galactic plane inside the bar region. NGC 6540 instead shows a completely different orbital behaviour, having a dynamical signature of the thick disc. Both prograde and prograde–retrograde orbits with respect to the direction of the Galactic rotation were revealed, which might characterise a chaotic behaviour.
A view of the Galactic bulge by means of their globular clusters is fundamental for a deep understanding of its formation and evolution. Connections between the globular cluster and field star properties in terms of kinematics, orbits, chemical abundances, and ages should shed light on different stellar population components. Based on spatial distribution and metallicity, we define a probable best list of bulge clusters, containing 43 entries. Future work on newly discovered objects, mostly from the VVV survey, is suggested. These candidates might alleviate the issue of missing clusters on the far side of the bulge. We discuss the reddening law affecting the cluster distances towards the centre of the Galaxy, and conclude that the most suitable total-to-selective absorption value appears to be RV=3.2, in agreement with recent analyses. An update of elemental abundances for bulge clusters is provided.
Very few abundance analyses of individual stars in metal-poor globular clusters in the galactic bulge are available. The main purpose of this study is to derive abundances in individual stars of such clusters, in order to establish their abundance pattern, trying to characterize the oldest bulge stellar populations.
Open cluster remnants (OCRs) are fundamental objects to investigate open cluster dissolution processes (e.g., Bica et al. 2001; Carraro 2002; Pavani et al. 2003; Carraro et al. 2007; Pavani & Bica 2007). They are defined as poorly populated concentrations of stars, with enough members to show evolutionary sequences in colour–magnitude diagrams (CMDs) as a result of the dynamical evolution of an initially more massive physical system. An OCR is intrinsically poorly populated, which makes its differentiation from field-star fluctuations difficult. Among the possible approaches to establish the nature of OCRs, we adopted CMD analysis combined with a robust statistical tool applied to 2mass data. In addition, photometry is the main information source available for possible OCRs (POCRs). We developed a statistical diagnostic tool to analyse the CMDs of POCRs and verify them as physical systems, explore membership probabilityies taking into account field contamination and derive age, distance and reddening values in a self-consistent way. We present the results of our analysis of 88 POCRs that are part of a larger sample that is widely distributed across the sky, with a significant density contrast of bright stars compared to the Galactic field. The 88 objects are projected onto low-density Galactic fields, at relatively high latitudes (|b| > 15°). Studies of larger POCR samples will provide a better understanding of OCR properties and constraints for theoretical models, including new insights into the evolution of open clusters and their dissolution rates. The results of this ongoing survey will provide a general picture of these fossil stellar systems and their connection to Galactic-disk evolution.
We present flux-calibrated integrated spectra in the optical spectral range of Galactic open clusters (GOCs) and Magellanic Cloud (MC) stellar clusters (SCs) obtained at CASLEO (Argentina). The SC parameters were derived using the equivalent-width (EW) method and the template-matching procedure by comparing the line strengths and continuum distribution of the cluster spectra with those of template spectra with known parameters. MC cluster reddening values were also estimated by interpolation between the available extinction maps. The derived ages for the GOCs range from 3 Myr to 4 Gyr, while those of the MC SCs vary from 3 Myr to 7 Gyr. E(B−V) colour-excess values in the MCs appear to be all lower than 0.17 mag, while those of the GOCs range from 0.00 to 2.40 mag. The present data led us to upgrade the spectral libraries of reference spectra or templates of solar and MC metallicities.
A detailed abundance analysis of four giants in the metal-rich bulge globular cluster NGC 6553 is carried out, based on optical high resolution échelle spectra obtained with UVES at the ESO VLT-UT2 Kueyen telescope. A mean radial heliocentric velocity of −1.86 km s−1 is found. Stellar parameters are derived from spectroscopic data based on Fe I and Fe II lines. Enhanced abundance ratios for the α-elements Mg and Si with respect to Ca and Ti are obtained. The odd-Z elements are typically solar. A solar value for the r-process element Eu ([Eu/Fe] = +0.05 ±0.06) was also found.
The properties of the globular clusters located within 20° × 20° of the Galactic Center are discussed. In particular their spatial distribution, metallicities and ages are presented and discussed in the context of different scenarios of bulge formation.
The knowledge of age and spatial distribution of stars in the Galactic bulge require observational constraints to establish whether its stellar population is very old (Larson 1990) or is a younger, disk-like component (Raha et al. 1992), and if its shape is spherical or extended, or perhaps a bar (Blitz & Spergel 1991). Yet other possibilities are a flattened bulge or a disk-like system (Zinn 1985; Armandroff 1989; Ortolani et al. 1993; Minniti 1995).
Globular clusters in the Galactic bulge form a flattened system, extending from the Galactic center to about 4.5 kpc from the Sun (Barbuy et al. 1997). A study of abundance ratios in these clusters is very important for a more complete understanding of the bulge formation. In this work we present a spectroscopic analysis of individual stars in NGC 6553. This cluster is a key one because it is located at d⊙ ≍ 5.1 kpc, therefore relatively close to us, and at the same time it is representative of the Galactic bulge stellar population: (a) Ortolani et al. (1995) showed that NGC 6553 and NGC 6528 show very similar Colour-Magnitude Diagrams (CMDs), and NGC 6528 is located at d⊙ ≍ 7.83 kpc, very close to the Galactic center; (b) the stellar populations of the Baade Window is also very similar to that of NGC 6553 and NGC 6528 as Ortolani et al. (1995) have shown by comparing their luminosity functions.
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.
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).
We have obtained CCD BVRI colour-magnitude diagrams for a series of disk globular clusters, improving parameters and detecting a new one: Lyngå 7. Using the magnitude difference between turn-off and horizontal branch Δ(TO-HB) as an age discriminator, and their spatial distribution we compare old disk open clusters, young halo globular clusters, and metal-rich disk globular clusters, obtaining clues to the Galaxy formation process.
CCD échelle spectra in the wavelength range λλ 478 – 580 nm, were obtained at the 3.6m telescope at ESO for the star III-17 of the metal-rich globular cluster NGC 6553. This cluster was chosen because it is a relatively close bulge globular cluster, and it presented the possibility to be among the most metal-rich ones in the Galaxy.
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