1,721,123 research outputs found
Near-Infrared Properties of 24 Globular Clusters in the Galactic Bulge
No full textWe present near-IR color-magnitude diagrams and physical parameters for a sample of 24 Galactic globular clusters toward the bulge. In this paper we discuss the properties of 12 new clusters (out of the 24) in addition to those previously studied and published by our group. The compilation includes measurements of the cluster reddening, distance, photometric metallicity, horizontal branch red clump, and red giant branch morphological (e.g., mean ridgelines) and evolutionary (e.g., bump and tip) features. The compilation is available in electronic form on the World Wide Web, and it will be updated regularly
Near-infrared photometry of four metal-rich bulge globular clusters: NGC 6304, 6569, 6637 and 6638
No full textWe present high-quality near-infrared (near-IR) photometry of four bulge metal-rich globular clusters, namely NGC 6304, 6569, 6637 and 6638. By using the observed colour-magnitude diagrams we derived photometric estimates of the cluster reddening and distance. We performed a detailed analysis of the red giant branch (RGB), presenting a complete description of its morphologic parameters and evolutionary features (bump and tip). Photometric estimates of the cluster metallicity were obtained using the updated data set (published by our group) linking metal abundance to a variety of near-IR indices measured along the RGB. The detection of the RGB bump and tip is also presented and briefly discusse
Red giant branch in near-infrared colour-magnitude diagrams - II. The luminosity of the bump and the tip
No full textWe present new empirical calibrations of the red giant branch (RGB) bump and tip based on a homogeneous near-infrared data base of 24 Galactic globular clusters. The luminosities of the RGB bump and tip in the J, H and K bands and their dependence on the cluster metallicity have been studied, yielding empirical relationships. By using recent transformations between the observational and theoretical planes, we also derived similar calibrations in terms of bolometric luminosity. Direct comparisons between updated theoretical models and observations show an excellent agreement. The empirical calibration of the RGB tip luminosity in the near-infrared passbands presented here is a fundamental tool to derive distances to galaxies far beyond the Local Group, in view of using the new ground-based adaptive optics facilities and, in the near future, the James Webb Space Telescope
Near-infrared properties of 12 globular clusters towards the inner bulge of the Galaxy
No full textWe present near-infrared colour-magnitude diagrams and physical parameters for a sample of 12 galactic globular clusters located towards the inner bulge region. For each cluster we provide measurements of the reddening, distance and photometric metallicity and of the luminosity of the horizontal branch red clump and the red giant branch bump and tip. The sample discussed here, together with that presented in Valenti, Ferraro & Origlia (2007), represents the largest homogeneous catalogue of bulge globular clusters (comprising ~80 per cent of the entire bulge cluster population) ever studied
Near-infrared photometry and spectroscopy of NGC 6539 and UKS 1: two intermediate metallicity bulge globular clusters
No full textUsing the `son of ISAAC' (Infrared Spectrometer And Array Camera) imager at the European Southern Observatory New Technology Telescope and the near-infrared spectrographs on Keck II, we have obtained J, K images and echelle spectra covering the range 1.5-1.8mum for the intermediate metallicity bulge globular clusters NGC 6539 and UKS 1. We find [Fe/H]=-0.76 and -0.78, respectively, and an average alpha-enhancement of ~+0.44 and ~+0.31 dex, consistent with previous measurements of metal-rich bulge clusters, and favouring the scenario of rapid chemical enrichment. We also measure very low 12C/13C ~ 4.5 +/- 1 isotopic ratios in both clusters, suggesting that extra-mixing mechanisms due to cool bottom processing are at work during evolution along the red giant branch. Finally, we measure accurate radial velocities of =+31 +/- 4 and =+57 +/- 6 km s-1 and velocity dispersions of ~8 and ~11 km s-1 for NGC 6539 and UKS 1, respectivel
Looking Outside the Galaxy: The Discovery of Chemical Anomalies in Three Old Large Magellanic Cloud Clusters
No full textBy using the multifiber spectrograph FLAMES mounted at the ESO-VLT, we have obtained high-resolution spectra for 18 giant stars, belonging to three old globular clusters of the Large Magellanic Cloud (namely NGC 1786, 2210, and 2257). While stars in each cluster showed quite homogeneous iron content, within a few cents of dex (the mean values being [Fe/H]= -1.75 ± 0.01 dex, -1.65 ± 0.02 dex and -1.95 ± 0.02 dex for NGC 1786, 2210, and 2257, respectively), we have detected significant inhomogeneities for the [Na/Fe], [Al/Fe], [O/Fe], and [Mg/Fe] abundance ratios, with evidence of [O/Fe] versus [Na/Fe] and [Mg/Fe] versus [Al/Fe] anticorrelations. The trends detected nicely agree with those observed in Galactic Globular Clusters, suggesting that such abundance anomalies are ubiquitous features of old stellar systems and they do not depend on the parent galaxy environment. In NGC 1786 we also detected two extreme O-poor, Na-rich stars. This is the first time that a firm signature of extreme chemical abundance anomalies has been found in an extragalactic stellar cluster
The Globular Cluster NGC 1978 in the Large Magellanic Cloud
No full textWe have used deep, high-resolution Hubble Space Telescope ACS observations to image the cluster NGC 1978 in the Large Magellanic Cloud. This high-quality photometric data set allowed us to confirm the high ellipticity (?~0.30+/-0.02) of this stellar system. The derived color-magnitude diagram allowed a detailed study of the main evolutionary sequences; in particular, we have detected the so-called bump along the red giant branch (at V555=19.10+/-0.10). This is the first detection of this feature in an intermediate-age cluster. Moreover, the morphology of the evolutionary sequence and the population ratios have been compared with the expectations of different theoretical models (namely, BaSTI, Pisa Evolutionary Library [PEL], and Padua) in order to quantify the effect of convective overshooting. The best agreement (in terms of both morphology and star counts) has been found within the PEL isochrone, with Z=0.008 (consistent with the most recent determination of the cluster metallicity, [M/H]=-0.37 dex) and a mild overshooting efficiency (?os=0.1). By adopting this theoretical set an age of ?=1.9+/-0.1 Gyr has been obtained
The Chemical Composition of Red Giant Stars in Four Intermediate-Age Clusters of the Large Magellanic Cloud
No full textThis paper presents the chemical abundance analysis of a sample of 27 red giant stars located in four populous intermediate-age globular clusters in the Large Magellanic Cloud, namely NGC 1651, 1783, 1978, and 2173. This analysis is based on high-resolution (R~ 47,000) spectra obtained with the UVES@VLT spectrograph. For each cluster we derived up to 20 abundance ratios sampling the main chemical elemental groups, namely light odd-Z, α, iron-peak, and neutron-capture elements. All the analyzed abundance patterns behave similarly in the four clusters and also show negligible star-to-star scatter within each cluster. We find [Fe/H] = 0.30 ± 0.03, 0.35 ± 0.02, 0.38 ± 0.02, and 0.51 ± 0.03 dex for NGC 1651, 1783, 1978, and 2173, respectively. The measurement of light odd-Z nuclei gives slightly subsolar [Na/Fe] and a more significant [Al/Fe] depletion (~ 0.50 dex). The [α/Fe] abundance ratios are nearly solar, while the iron-peak elements well trace those of the iron. S-process elements behave in a peculiar way: light s-elements give subsolar [Y/Fe] and [Zr/Fe] abundance ratios, while heavy s-elements give enhanced [Ba/Fe], [La/Fe], and [Nd/Fe] with respect to the solar values. Also, the [Eu/Fe] abundance ratio turns out to be enhanced (~0.4 dex)
High-Resolution Infrared Spectroscopy of the Old Open Cluster NGC 6791
No full textWe report abundance analysis for six M giant members of the old open cluster NGC 6791, based on infrared spectroscopy (1.5-1.8 mum) at R=25,000, using the NIRSPEC spectrograph at the Keck II telescope. We find the iron abundance =+0.35+/-0.02, confirming the supersolar metallicity of this cluster as derived from optical medium-high resolution spectroscopy. We also measure C, O, and other alpha-element abundances, finding a roughly solar value of [alpha/Fe] and =-0.35. Our approach constrains [O/Fe] especially well, on the basis of the measurement of a number of OH lines near 1.6 mum we find [O/Fe]=-0.07+/-0.03. The solar value of [alpha/Fe] is in contrast to the composition of similar stars in the Galactic bulge. We also find a low value of 12C/13C~10, confirming the presence of extramixing processes during the red giant phase of evolution, up to supersolar metallicities
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