We recently presented (Sbordone et al., 2009a) the largest sample to date of lithium abundances in extremely metal-poor (EMP) Halo dwarf and Turn-Off (TO) stars. One of the most crucial aspects in estimating Li abundances is the Teff determination, since the Li I 670.8 nm doublet is highly temperature sensitive. In this short contribution we concentrate on the Teff determination based on Hα wings fitting, and on its sensitivity to the chosen stellar gravity.

The abundance derivation of heavy r-elements may provide a better understanding of the r-process, and the determination of several reference r-elements should allow a better determination of the star's age. The spatial ultraviolet (UV) region presents a large number of lines of heavy elements, and in some cases such as Bi, Pt, Au, detectable lines are only available in the UV. The extreme “r-process star” CS 31082-001 ([Fe/H] = −2.9) was observed in the spatial UV in order to determine abundances of the heavy elements, using STIS on board HST.

In the framework of he ESO Large Program “First Stars”, high resolution (R=45000) high S/N ratio spectra have been obtained for a sample of Extremely Metal Poor Stars (EMP stars), 35 giants and 18 turnoff stars. Among them 37 have a very low metallicity: [Fe/H]< −2.9.

We present the largest sample available to date of lithium abundances in extremely metal poor (EMP) Halo dwarfs. Four Teff estimators are used, including IRFM and Hα wings fitting against 3D hydrodynamical synthetic profiles. Lithium abundances are computed by means of 1D and 3D-hydrodynamical NLTE computations. Below [Fe/H]~−3, a strong positive correlation of A(Li) with [Fe/H] appears, not influenced by the choice of the Teff estimator. A linear fit finds a slope of about 0.30 dex in A(Li) per dex in [Fe/H], significant to 2–3 σ, and consistent within 1 σ among all the Teff estimators. The scatter in A(Li) increases significantly below [Fe/H]~−3. Above, the plateau lies at 〈A(Li)3D, NLTE〉 = 2.199 ± 0.086. If the primordial A(Li) is the one derived from standard Big Bang Nucleosynthesis (BBN), it appears difficult to envision a single depletion phenomenon producing a thin, metallicity independent plateau above [Fe/H] = −2.8, and a highly scattered, metallicity dependent distribution below.

From NLTE computations of the magnesium abundance in a sample of extremely metal-poor giants we derive [Mg/Fe]=+0.7, leading to [Al/Mg]=−0.80 and [Na/Mg]=−0.85 in the early Galaxy. The ratio [O/Mg] should be near to the solar value. Measurements of nitrogen abundances derived from the analysis of the NH band in eight more stars confirm the large scatter of the ratios [N/Fe] and [N/O] in the early Galaxy.

We have studied the lithium abundance in 18 extremely metal-poor main-sequence turnoff stars as a function of [Fe/H] and $T_{\rm eff}$, using high-quality VLT/UVES spectra. The sample covers the range $-3.3\le [{\rm Fe}/{\rm H}]\le -2.5$, with half of the stars below [Fe/H] = −3.0. $T_{\rm eff}$ is determined from H$\alpha$ line profiles as well as from B-V, V-K, J-H and J-K colours. The behaviour of A(Li) as a function of metallicity is markedly different when different temperature scales are adopted. However, even when applying standard depletion corrections, it is a robust result that the Li abundance in extremely metal poor dwarfs is far below the prediction of standard big bang nucleosynthesis using a baryonic density consistent with the WMAP data.

We present briefly some results of the ESO Large Program “First Stars"where it is shown that the abundance ratios of some light elements in theatmospheres of the extremely metal poor stars varies when the starevolves. This could be explained by a mixing with deep layers butsuch a mixing is not predicted by the theory.

High dose helium implantation followed by a suitable thermal treatment induces defects such as cavities and dislocations. Gettering efficiency of this technique for metallic impurities has been widely proved. Nevertheless, dopants, as well as point defects, interact with this defect layer. Due to the presence of vacancy type defects after helium implantation, boron diffusion can be largely influenced by such a buried layer. In this paper, we study the influence of helium induced defects on boron diffusion. The boron diffusion in presence of these defects has been analyzed as a function of different parameters such as distance between boron profile and defect layer and defect density. Our results demonstrate that the major impact known as boron enhanced diffusion can be partially or completely suppressed depending on parameters of experiments. Moreover, these results clarify the interaction of boron with extended He-induced defects.

The use of gettering techniques that can be precisely localized in the component, such as neutral element implantation, has become crucial for power device manufacturing. High-dose helium implantation in silicon with a subsequent annealing induces defects (cavities and dislocations) which are able to getter metallic impurities and interact with dopants. These interactions can become a drawback of this technique. In this work, Si wafers $\langle 111\rangle$ -oriented, p-doped with a concentration in between 6 × 1014 and 8 × 1018 B/cm3, were used. Iron contamination was performed by backside implantation (100 keV and 1012 Fe cm−2). Helium implantation was performed at 40 keV and 5 × 1016 at cm−2 at room temperature and followed by a Furnace Annealing (FA) stage. Secondary Ion Mass Spectrometry (SIMS) was used to study the dopant/metal/cavity layer system. In this paper, we will focus on the cavity layer interactions with both metals and dopant impurities. Our experimental results exhibit a large segregation of both species within the cavity layer that occurs during the annealing stage. Both species segregate simultaneously in helium-implanted samples without interacting one to the other. The number of gettering sites does not limit the trapping reactions.

High dose He implantation, followed by a thermal annealing, is a suitable technique for metal gettering. Nevertheless, a strong interaction between the dopants and the defect layer has been evidenced. This can largely influence the dopant distribution. In order to study this interaction, p and n-type samples uniformly doped were implanted with helium (40 keV, 5×1016 He+.cm-2) and furnace annealed for various times and temperatures. In this paper, we shed light on the evolution of the dopant segregation. Using isochronal treatment, we found a large dependence of the dopant gettering phenomenon upon annealing temperature. Moreover, stability of the gettered fraction is observed for isothermal annealing. This study permits also to investigate the origin of the trapping mechanism involved for both boron and phosphorus.

We present a determination of the lithium abundance from high quality spectra in an extremely metal poor star where the lithium line had not been detected.

From models of the Sun atmosphere obtained with ATLAS 9 (Kurucz 1992) it appears that the diffusion limit of the transfer equation becomes valid only at depths larger than TR ~ 10. Even with physics as consistent as possible one restores the atmosphere with an accuracy not better than ~ 40%, but with small consequences on solar calibrated models. Despite the eigenmodes have turning points located in the atmosphere, the study of the oscillations reveals differences less than 2μHz when the atmosphere is restored with various assumptions.

NEW data about dwarfs: a few more metal-poor dwarfs have been observed for lithium at the CAT + CES at La Silla (ESO). These new results, together with a few new measurements in the literature show again a constant lithium abundance, confirming the trend previously found (the plateau). Let us note however that two metal-poor dwarfs have recently been reported with a low lithium abundance. Obviously, more observations are needed.

While a number of site testing campaigns are in progress throughout the world, the dominant efforts seem to be associated with plans for very large telescopes. These plans, improved telescope technology, and the realization that astronomical observations from space will put increasing demands on ground-based observing facilities have given new impetus to site identification and to the optimum utilization of existing sites. A most excellent review of the factors involved in site identification is now available in the Proceedings of the ESO Workshop on Site Testing for Future Large Telescopes, edited by A. Ardeberg and L. Woltjer 1981. These Proceedings and Woolf’s review (1982, Ann. Rev. Astron. Astrophys. 20 367) provide a solid background of current site evaluation factors.