The presence of multiple populations in globular clusters has been well established thanks to high-resolution spectroscopy. It is widely accepted that distinct populations are a consequence of different stellar generations: intra-cluster pollution ep
isodes are required to produce the peculiar chemistry observed in almost all clusters. Unfortunately, the progenitors responsible have left an ambiguous signature and their nature remains unresolved. To constrain the candidate polluters, we have measured lithium and aluminium abundances in more than 180 giants across three systems: NGC~1904, NGC~2808, and NGC~362. The present investigation along with our previous analysis of M12 and M5 affords us the largest database of simultaneous determinations of Li and Al abundances. Our results indicate that Li production has occurred in each of the three clusters. In NGC~362 we detected an M12-like behaviour, with first and second-generation stars sharing very similar Li abundances favouring a progenitor that is able to produce Li, such as AGB stars. Multiple progenitor types are possible in NGC~1904 and NGC~2808, as they possess both an intermediate population comparable in lithium to the first generation stars and also an extreme population, that is enriched in Al but depleted in Li. A simple dilution model fails in reproducing this complex pattern. Finally, the internal Li variation seems to suggest that the production efficiency of this element is a function of the clusters mass and metallicity - low-mass or relatively metal-rich clusters are more adept at producing Li.
We present stellar parameters and abundances of 11 elements (Li, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, and Zn) of 13 F6-K2 main-sequence stars in the young groups AB Doradus, Carina Near, and Ursa Major. The exoplanet-host star iota Horologii is also a
nalysed. The three young associations have lithium abundance consistent with their age. All other elements show solar abundances. The three groups are characterised by a small scatter in all abundances, with mean [Fe/H] values of 0.10 (sigma=0.03), 0.08 (sigma=0.05), and 0.01 (sigma=0.03) dex for AB Doradus, Carina Near, and Ursa Major, respectively. The distribution of elemental abundances appears congruent with the chemical pattern of the Galactic thin disc in the solar vicinity, as found for other young groups. This means that the metallicity distribution of nearby young stars, targets of direct-imaging planet-search surveys, is different from that of old, field solar-type stars, i.e. the typical targets of radial velocity surveys. The young planet-host star iota Horologii shows a lithium abundance lower than that found for the young association members. It is found to have a slightly super-solar iron abundance ([Fe/H]=0.16+-0.09), while all [X/Fe] ratios are similar to the solar values. Its elemental abundances are close to those of the Hyades cluster derived from the literature, which seems to reinforce the idea of a possible common origin with the primordial cluster.
Recent surveys confirm early results about a deficiency or even absence of CN-strong stars on the asymptotic giant branch (AGB) of globular clusters (GCs), although with quite large cluster-to-cluster variations. In general, this is at odds with the
distribution of CN band strengths among first ascent red giant branch (RGB) stars. Norris et al. proposed that the lack of CN-strong stars in some clusters is a consequence of a smaller mass of these stars that cannot evolve through the full AGB phase. In this short paper we found that the relative frequency of AGB stars can change by a factor of two between different clusters. We also find a very good correlation between the minimum mass of stars along the horizontal branch (Gratton et al. 2010) and the relative frequency of AGB stars, with a further dependence on metallicity. We conclude that indeed the stars with the smallest mass on the HB cannot evolve through the full AGB phase, being AGB-manque. These stars likely had large He and N content, and large O-depletion. We then argue that there should not be AGB stars with extreme O depletion, and few of them with a moderate one.
Determining the metal content of low-mass members of young associations provides a tool that addresses different issues, such as triggered star formation or the link between the metal-rich nature of planet-host stars and the early phases of planet fo
rmation. The Orion complex is a well known example of possible triggered star formation and is known to host a rich variety of proto-planetary disks around its low-mass stars. Available metallicity measurements yield discrepant results. We analyzed FLAMES/UVES and Giraffe spectra of low-mass members of three groups/clusters belonging to the Orion association. Our goal is the homogeneous determination of the metallicity of the sample stars, which allows us to look for [Fe/H] differences between the three regions and for the possible presence of metal-rich stars. Nine members of the ONC and one star each in the $lambda$ Ori cluster and OB1b subgroup were analyzed. After the veiling determination, we retrieved the metallicity by means of equivalent widths and/or spectral synthesis using MOOG. We obtain an average metallicity for the ONC [Fe/H]=-0.01pm 0.04. No metal-rich stars were detected and the dispersion within our sample is consistent with measurement uncertainties. The metallicity of the $lambda$ Ori member is also solar, while the OB1b star has an [Fe/H] significantly below the ONC average. If confirmed by additional [Fe/H] determinations in the OB1b subgroup, this result would support the triggered star formation and the self-enrichment scenario for the Orion complex.
