Globular clusters

A few comments can be drawn from the abundance results presented in Figure 1. The abundances obtained for the red giants in the globular cluster iv Cen-tauri seem to indicate the existence of a sharp decline in the [F/O] ratios as the metallicity approaches the lowest observed oxygen abundance in this globular... 

Abstract. A review is presented on abundance determinations in stars of the Galactic bulge, both in the field and in globular clusters. Previous low-resolution spectroscopy results are revised. Recent high resolution and high S/N spectroscopy results based on Keck-Hires, Gemini-Phoenix and VLT-UVES data are presented. Finally, recent analyses of FLAMES data are discussed. 

The metallicity distribution of globular clusters in the Galaxy has a metal-rich peak at [Fe/H] -0.5 and a metal-poor peak at [Fe/H] -1.6 (e.g. Cote 1999), where most of the metal-rich ones are bulge clusters. Metallicities for samples of field stars were derived by McWilliam Rich (1994, hereafter MR94), Sadler et al. (1996), Ramirez et al. (2000). Zoccali et al. (2003) presented the... 

Fig. 2. [O/Fe] vs. [Fe/H] for bulge globular clusters in a range of metallicities, and including 47 Tuc for comparison...

Among the sample of outer halo stars being investigated are Keck I HIRES observations of four globular clusters with [Fe/H] -2. Information regarding these clusters and comparison objects is presented in Table 1. 

In addition to results from this study, Table 1 includes two of the relatively more metal-rich globular clusters associated with the Sgr dSph. There appears to be little in common between the two metallicity groups in their < a>-abundances relative to iron. Abundances reported so far for in situ Sgr dSph field stars of comparable metallicities [4] are in accord with those of its metal-rich clusters. 

C. Sneden, I. I. Ivans, J. P. Fulbright Globular Clusters and Halo Field Stars . In Origin and Evolution of the Elements Volume 4, Carnegie Observatories Astrophysics Series, ed. by A. McWilliam, M. Rauch (Cambridge, 2004)... 

Chemical Abundance Inhomogeneities in Globular Cluster Stars... 

Fig. 1. The range of [C/Fe] (left panel) and [N/Fe] (right panel) is shown as a function of metallicity ([Fe/H]) for the globular clusters from our work on M71, M5, M13, and M15 as well as for 47 Tuc (from Briley et al 2004a). Large samples of stars, mostly subgiants, were used in each case. Each GC is represented by a horizontal line. The characteristic field star ratio, from Carretta, Gratton Sneden (2000) for C and from Henry, Edmunds Koppen (2000) for N, are indicated by vertical arrows in each panel.

Most of the stars of our sample have been selected from the H K BPS survey ( Beers, Preston Shectman [1], First, stars were selected from the weakness of their H H lines for the Balmer lines intensity on prism-objective Schmidt telescope plates. Then, the candidate stars were observed with a slit spectrograph in order to have a quantitative estimate of their metallicity. The survey has operated on about 7000 square degrees of the sky, mostly on the polar caps. It has supply a vast amount of metal-poor stars, with hundreds of them more metal-poor than the most metal-poor globular clusters. We selected from this sample stars with metallicities estimated to have [Fe/H] < -2.7. The actual metallicity histogram is given for the sample on fig. 1. 

Heavy Elements and Chemical Enrichment in Globular Clusters... 

Spectroscopic observations of globular clusters (GCs) have revealed star-to-star inhomogeneities in the light metals that are not observed in field stars. These light metal anomalies could be interpreted with a self-pollution scenario. But what about heavier (Z > 30) elements Do they also show abundance anomalies Up to now, no model has been developed for the synthesis of n-capture elements in GCs, and the self-pollution models do not explain the origin of their metallicity. In 1988, Truran suggested a test for the self-enrichment scenario [4], which could possibly explain the metallicity and the heavy metal abundances in GCs if self-enrichment occurred in GCs, even the most metal-rich clusters would show both high [a/Fe] ratios and r-process dominated heavy elements patterns, which characterize massive star ejecta as it is seen in the most metal-poor stars. 

Reid stars eJAM04 BUROO. FUL00 "MAS01.03 Globular clusters SG A TO Others... 

The sample has been cleaned of 5 suspected binaries and of 6 stars with a 215sample contains 217 stars. The RV distribution is shown in Figure 1. The associated errors are smaller than 0.45 km.s-1, with a mean error value of 150 m.s-1. 

Chemical Abundances of Three Metal-Poor Globular Clusters in the Inner Halo... 

Abstract. The observations of light elements (Lithium and Beryllium) in Globular Cluster (GC) stars are reviewed. Light element observations in GC are very powerful tracers of mixing processes in the stellar interior and shed new light on the GC formation history. 

Globular clusters are quite distant and their turnoff (TO) stars are intrinsically relatively faint. Following the advent of state-of-the-art instrumentation in 4m class telescopes, the first Li observations were carried on in GC stars, while with the advent of 8m class telescopes a quality jump occurred high quality spectra can now be obtained for the TO stars of the closest clusters, comparable to that available for field stars. In spite of this advancement, only a handful of published refereed papers have been devoted to the study of Li in globular cluster stars, and only one to beryllium. Based upon the wealth of information made available as a result of this data, I will present new findings concerning stellar mixing, primordial Li production and GC formation. 

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