Globular cluster stars exhibit abundance anomalies which are not shared by their field counterparts. Two global scenarii have been proposed in the past to explain these differences: The primordial enrichment scenario and the evolutionary (or intrinsic) one. Recent observations well below the bump luminosity in globular clusters have raised the weight of the primordial solution. However the stellar sources responsible for these abundance variations have not yet been indubitably identified. In this review we discuss the possible stellar culprits as well as their pros and cons.

We present preliminary results of a few observing programs conducted with the FLAMES fiber facility at VLT2 ESO telescope. These programs show the large potentiality of FLAMES for investigations of globular clusters. The programs described here concern the derivation of precise reddening and metallicity for globular clusters, and the derivation of abundances for stars on the main sequence of ω Cen. Reddenings with errors of $\Delta E(B-V)=0.005$ mag and metallicities with errors of ±0.02 dex (in a scale defined by local subdwarfs) can be obtained in very short observing time. Our results for ω Cen show that the blue main sequence is more metal-rich than the red-main sequence: this requires a large He-content for the blue main sequence.

Lithium abundance in Turnoff stars of Globular Clusters (GC) provide precious information about primordial nucleosynthesis and Globular Cluster formation. Out of the three GC so far observed in some detail, the metal poor NGC6397 shows a constant Li abundance, at the same level of the Spite' plateau; while the more metal rich NGC6752 and 47 Tuc show a beautiful Li-Na anticorrelation (the first of this kind observed in PoP II stars), suggesting the presence of gas processed by a previous generation of stars. These observations are quite puzzling: while they are qualitatively compatible with the scenario of contamination from intermediate mass AGB stars, no progenitor can quantitatively reproduce the observations. Beryllium has also been detected in NGC6397 Turnoff stars, indicating that the gas which formed the stars was exposed for about 200 Myr to the Galactic Cosmic Rays. The emerging picture seems to require that in the early Galaxy both local (SNae, AGB stars) and global (Galactic Cosmic Rays) enrichment processes were acting simultaneously in the star formation phase of the halo.

Using the 2dF multi-fibre instrument on the Anglo-Australian Telescope, moderate resolution spectra have been obtained for a large sample of stars on the main sequence and at the turnoff in the unusual globular cluster ω Cen. We investigate the behaviour of CH, CN and SrII line strength indices as a function of overall abundance for the main sequence sample. A number of stars do not follow the relations defined by the majority. These anomalous objects can be categorized into (at least) three types. (1) Carbon enhanced stars, which represent about 5% of the sample, and which are found at all metallicities. Spectrum synthesis calculations show that the atmospheres of these stars are typically enhanced in carbon by factors of between 3 and 10. (2) Nitrogen enhanced stars, revealed for [Fe/H] [ges ]–1.3 by strong CN indices, which make up ∼40% of the cluster main sequence population above this metallicity. The stars are enhanced in nitrogen by factors of up to 100. Our data, however, provide no constraints on their relative numbers at lower [Fe/H]. (3) Stars with enhancements of the s-process element Sr by factors of 30 to 60. The possible origins for these abundance anomalies are discussed.

Abundance variations in globular clusters have been observed for the light elements C, N, O, Na, Al, as well as sometimes Mg. Such variations can be understood as the result of H-burning. In particular for the globular cluster M4, anticorrelations of O with Na and Al have been established from previous studies. In this study, we discuss fluorine abundances in a sample of M4 red-giants derived from infrared high-resolution spectra obtained with Pheonix on Gemini South. Our results show that fluorine now can be added to the suite of elements that are shown to vary in M4: the abundance of 19F is found to be anti-correlated with the sodium and aluminium variations. These results provide further evidence that H-burning is indeed responsible for the observed chemical inhomegeneities. Moreover, from comparisons with stellar models, tighter constraints on the mass of the polluting star in this globular cluster are extablished.

We have derived Mn abundances for more than 200 stars in nineteen globular clusters. In addition, Mn abundance determinations have been made for a comparable number of halo field stars possessing an overlapping range of metallicities and stellar parameters. The primary data set was comprised of high resolution spectra previously-acquired at the McDonald, Lick and Keck Observatories. Additional data were obtained from several other investigators. Data were analyzed using synthetic spectra of the 6000 Å Mn I triplet. Hyperfine structure parameters were included in the synthetic spectra computations. Our analysis shows that over the metallicity range $-0.7>[Fe/H]-2.7$ field stars have a mean relative abundance of $<[Mn/Fe]>=-0.36$ identical to that of the nineteen globular clusters $<[Mn/Fe]>=-0.36$. Our Mn abundance results viewed in conjunction with the globular cluster Cu abundances of Simmerer et al. (2003) suggest the following possibilities: one, the production of these elements is highly metallicity-dependent or two, these elements were manufactured in the Galactic halo prior to formation of present-day globular clusters.

Despite its importance, the Galactic Bulge and its globular cluster (GC) system in particular, remain relatively unexplored due to high foreground extinction and severely crowded field populations. The new generation of high resolution IR spectrographs opens new and unique perspectives to obtain detailed abundances in the Bulge field and GCs. Using the NIRSPEC spectrograph at Keck II, high resolution, echelle spectra in the range 1.5–1.8 micron of bright giants in the Baade's window and other fields closer to the Galactic center as well as in a sample of 10 Bulge GCs have been obtained. We present the results of our abundance analysis of Fe, Al, 12C, 13C, O, and other α-elements, by using full spectral synthesis techniques.

We present here the first results (on NGC 2808 and NGC 6752) of a program that studies the anticorrelation between Na and O in a sample of Galactic Globular Clusters, using GIRAFFE spectra obtained with UVES@VLT.

We summarize the results of recent model computation for massive Asymptotic Giant Branch stars of low metallicity, whose winds are thought to be the matter from which second generation stars are born in Globular Clusters (GCs) showing abundance anomalies. The yields of these ejecta are highly uncertain, but our models in the range of masses 3.5–4.5M[odot ] can reasonably explain some of the chemical anomalies of Globular Cluster stars.

Accurate relative abundances of light elements (C to Ca) have been obtained in a sample of mildly metal-poor stars (Decauwer et al. 2005). Combined with the results of a previous study (Jehin et al. 1999), we find different slopes in the correlations between the different α-elements. These results can be explained by postulating that the stars exhibiting lower than average α/Fe form in low mass clouds, unable to sustain the formation of very massive stars.

Stars in globular clusters exhibit abundance patterns such as the well-known O-Na and Mg-Al anticorrelations which have no counterpart among halo stars. Whereas winds from AGB stars have been proposed as the primordial sources for these anomalies, the impact of rotation in these stars has not been studied in the GC context. To address this issue we present a model of a rotating AGB star with an initial mass of 7 M[odot ] and a metallicity Z = 10−5. We discuss the effect of rotation on the evolutionary features, and focus on the surface abundances which can be modified by rotation, dredge-up events and hot bottom burning.

As part of a program of abundance studies of old open clusters, we present an analysis of high-dispersion echelle spectra of three giant stars in the 10 Gyr old cluster Berkeley 17. Abundances were determined relative to the disk giant Arcturus. Be 17 is found to have a mean [Fe/H] = −0.10 ±0.05 (mean error). Oxygen abundances, determined from the forbidden [O I] lines, show solar abundance ratios. The α-elements Mg, Ca, and Ti also show scaled solar abundance ratios, with suggestions that the Si abundance is slightly enhanced. The odd-Z elements Na and Al are significantly enhanced relative to scaled solar abundances. These abundance patterns are similar to those in two other 8-10 Gyr old open clusters, Cr261 and NGC 6791, and suggest that the Galactic disk was enriched to solar abundance levels at very early times.

Fundamental parameters and lithium abundances, ALi, have been derived for a sample of evolved stars in the globular cluster 47 Tuc (from GIRAFFE spectra and MARCS models of atmosphere). These data sample a complete evolutionary sequence from subgiant stage to the tip of the Asymptotic Giant Branch. With this unique observational data set we have analyzed the evolution of ALi along the Red Giant Branch (RGB) using non-standard stellar evolution models, so as to explore the occurence and the efficiency of extra-mixing processes in low mass stars at the so-called Red Giant bump.

We present elemental abundance ratios for red giant stars in 9 old halo globular clusters based on the homogeneous data sample and analysis method. Our result suggests that [Si/Ti] ratios in old globular clusters decrease with Galactocentric distances, confirming the previous result by Lee & Carney (2002). We propose that contributions from different masses of the Type II suprenovae progenitors that enriched proto-globular clusters' clouds are responsible for this gradient.

We have observed seven giants in the metal-poor globular cluster M15 using Subaru/HDS. We confirmed that there are significant star-to-star variations in the neutron-capture elemental abundances. This abundance variation means there were primordial chemical inhomogeneities in the proto-globular cluster cloud of M15. This result implies that there was insufficient time for complete mixing after r-process nucleosynthesis. It suggests that the main r-process occurs probably in supernovae which explode in later stages of globular cluster formation.

We determine the carbon isotopic ratios in the atmospheres of some evolved stars in both globular clusters and the disk of our Galaxy. Analysis of 12CO and 13CO bands at 2.3 micron was carried out using fits to observed spectra of red giants and Sakurai's object (V4334 Sgr). The dependence of theoretical spectra on the various input parameters was studied in detail. The computation of model atmospheres and a detailed abundance analysis was performed in a self-consistent fashion. A special procedure for determining the best fits to observed spectra was used. We show, that globular cluster giants with [Fe/H]$\,{<}\,{-}$1.3 have a low 12C/13C = 4 ±1 abundance ratios. In the spectra of Sakurai's object (V4334 Sgr) taken between 1997-98, the 2.3 micron spectral region is veiled by hot dust emission. By fitting UKIRT spectra we determined 12C/13C = 4 ±1 for the July, 1998 spectrum. CO bands in the spectra of ultracool dwarfs are modelled as well.

We have compiled a sample of globular clusters with high-resolution abundances from the literature to compare to the chemistries of stars in the Galaxy and those in dwarf spheroidal galaxies using the [α/Fe] and light r-process element ratios. From existing kinematic data we are able to analyze the populations according to their Galactic components (bulge, thin disk, thick disk, and halo). We find that most globular clusters mimic the Galactic field population arguing for a similar chemical evolution history. Possible extragalactic globular clusters are also noted.

In the context of a large observational project on old open clusters, we employed FLAMES + UVES on VLT UT2 to collect new high resolution spectra for giant stars in 7 clusters with the aim of investigating the radial abundance distributions in the Galactic disk. The gradients of Fe, α and Fe-peak elements and their evolution with Galactic age are indeed one of the most critical constraints to the star formation history in the Galactic disk and to Galactic chemical evolution models. We present here our preliminary results on the metallicity and abundance ratios for red clump stars in the ∼1 Gyr old cluster NGC 3960, located at a Galactocentric distance $R_{gc}\sim8$ kpc.

We present results of an extensive spectroscopic survey of Subgiant stars in the stellar system ω Centauri. Using infrared CaII triplet lines we derived metallicities and radial velocities for more than 250 stars belonging to different stellar populations of the system. A small age spread (<2 Gyr) among the stellar populations of ω Cen has been estimated regardless of any choice of helium abundance. These results impose severe constraints on the time-scale of the enrichment process of this stellar system, excluding the possibility of an extended star formation period. The radial velocities analysis of the entire sample demonstrates that only the metal-intermediate populations ($-1.4<[Fe/H]<-1.0$) are kinematically cooler than the others.

Eight cool giants in the unusual globular cluster NGC 6388 have been investigated in order to derive their elemental abundances. Average relative-to-solar abundance of iron is about –0.8. We have found that oxygen abundance is reduced as compared to most stars of a similar metallicity. The reduced carbon as compared to oxygen is at the level to be expected for red giant tip stars. Abundance of the rest of investigated elements are within the expected limits for the globular cluster stars.