Author name code: cayrel ADS astronomy entries on 2022-09-14 author:"Cayrel, Roger" ------------------------------------------------------------------------ Title: The 6Li/7Li isotopic ratio in the metal-poor binary CS22876-032 Authors: González Hernández, J. I.; Bonifacio, P.; Caffau, E.; Ludwig, H. -G.; Steffen, M.; Monaco, L.; Cayrel, R. Bibcode: 2019A&A...628A.111G Altcode: 2019arXiv190705109G
Aims: We present high-resolution and high-quality UVES spectroscopic data of the metal-poor double-lined spectroscopic binary CS 22876-032 ([Fe/H] approximately -3.7 dex). Our goal is to derive the 6Li/7Li isotopic ratio by analysing the Li I λ 670.8 nm doublet.
Methods: We co-added all 28 useful spectra normalised and corrected for radial velocity to the rest frame of the primary star. We fitted the Li profile with a grid of the 3D non-local thermodynamic equilibrium (NLTE) synthetic spectra to take into account the line profile asymmetries induced by stellar convection, and performed Monte Carlo simulations to evaluate the uncertainty of the fit of the Li line profile.
Results: We checked that the veiling factor does not affect the derived isotopic ratio, 6 Li/7Li, and only modifies the Li abundance, A(Li), by about 0.15 dex. The best fit of the Li profile of the primary star provides A(Li) = 2.17 ± 0.01 dex and 6 Li/7Li = 8-5+2% at 68% confidence level. In addition, we improved the Li abundance of the secondary star at A(Li) = 1.55 ± 0.04 dex, which is about 0.6 dex lower than that of the primary star.
Conclusions: The analysis of the Li profile of the primary star is consistent with no detection of 6 Li and provides an upper limit to the isotopic ratio of 6 Li/7Li < 10% at this very low metallicity, about 0.5 dex lower in metallicity than previous attempts for detection of 6 Li in extremely metal poor stars. These results do not solve or worsen the cosmological 7 Li problem, nor do they support the need for non-standard 6Li production in the early Universe.

The two averaged spectra are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/628/A111Based on observations made with the Very Large Telescope (VLT) at ESO Paranal Observatory, Chile, Programme 080.D-0333. Title: VizieR Online Data Catalog: Li in BPS CS22876-032 spectrum (Gonzalez Hernandez+, 2019) Authors: Gonzalez Hernandez, J. I.; Bonifacio, P.; Caffau, E.; Ludwig, H. -G.; Steffen, M.; Monaco, L.; Cayrel, R. Bibcode: 2019yCat..36280111G Altcode: Average co-added, rebinned spectra in the region around the LiI 670.8nm resonance line of the two stellar components of the metal-poor binary CS 22876-032 A and CS 22876-032 B. For each star, wavelength, normalised flux and flux error are given.

(2 data files). Title: TOPoS. V. Abundance ratios in a sample of very metal-poor turn-off stars Authors: François, P.; Caffau, E.; Bonifacio, P.; Spite, M.; Spite, F.; Cayrel, R.; Christlieb, N.; Gallagher, A. J.; Klessen, R.; Koch, A.; Ludwig, H. -G.; Monaco, L.; Plez, B.; Steffen, M.; Zaggia, S. Bibcode: 2018A&A...620A.187F Altcode: 2018arXiv181100035F Context. Extremely metal-poor stars are keys to understand the early evolution of our Galaxy. The ESO large programme TOPoS has been tailored to analyse a new set of metal-poor turn-off stars, whereas most of the previously known extremely metal-poor stars are giant stars.
Aims: Sixty five turn-off stars (preselected from SDSS spectra) have been observed with the X-shooter spectrograph at the ESO VLT Unit Telescope 2, to derive accurate and detailed abundances of magnesium, silicon, calcium, iron, strontium and barium.
Methods: We analysed medium-resolution spectra (R ≃ 10 000) obtained with the ESO X-shooter spectrograph and computed the abundances of several α and neutron-capture elements using standard one-dimensional local thermodynamic equilibrium (1D LTE) model atmospheres.
Results: Our results confirms the super-solar [Mg/Fe] and [Ca/Fe] ratios in metal-poor turn-off stars as observed in metal-poor giant stars. We found a significant spread of the [α/Fe] ratios with several stars showing subsolar [Ca/Fe] ratios. We could measure the abundance of strontium in 12 stars of the sample, leading to abundance ratios [Sr/Fe] around the Solar value. We detected barium in two stars of the sample. One of the stars (SDSS J114424-004658) shows both very high [Ba/Fe] and [Sr/Fe] abundance ratios (>1 dex).

Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programme ID 189.D-0165.

Equivalent widths of the Fe lines are only, and Tables A.1 and A.2 are also available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/620/A187 Title: VizieR Online Data Catalog: Very metal-poor turn-off stars abundances (Francois+, 2018) Authors: Francois, P.; Caffau, E.; Bonifacio, P.; Spite, M.; Spite, F.; Cayrel, R.; Christlieb, N.; Gallagher, A.; Klessen, R.; Koch, A.; Ludwig, H. -G.; Monaco, L.; Plez, B.; Steffen, M.; Zaggia, S. Bibcode: 2018yCat..36200187F Altcode: Sixty five turn-off stars (preselected from SDSS spectra) have been observed with the X-Shooter spectrograph at the ESO VLT Unit Telescope 2, to derive accurate and detailed abundances of magnesium, silicon, calcium, iron, strontium and barium. We analysed medium-resolution spectra (R~10000) obtained with the ESO X-Shooter spectrograph and computed the abundances of several alpha and neutron-capture elements using standard one-dimensional local thermodynamic equilibrium (1D LTE) model atmospheres.

(3 data files). Title: TOPoS. IV. Chemical abundances from high-resolution observations of seven extremely metal-poor stars Authors: Bonifacio, P.; Caffau, E.; Spite, M.; Spite, F.; Sbordone, L.; Monaco, L.; François, P.; Plez, B.; Molaro, P.; Gallagher, A. J.; Cayrel, R.; Christlieb, N.; Klessen, R. S.; Koch, A.; Ludwig, H. -G.; Steffen, M.; Zaggia, S.; Abate, C. Bibcode: 2018A&A...612A..65B Altcode: 2018arXiv180103935B Context. Extremely metal-poor (EMP) stars provide us with indirect information on the first generations of massive stars. The TOPoS survey has been designed to increase the census of these stars and to provide a chemical inventory that is as detailed as possible.
Aims: Seven of the most iron-poor stars have been observed with the UVES spectrograph at the ESO VLT Kueyen 8.2 m telescope to refine their chemical composition.
Methods: We analysed the spectra based on 1D LTE model atmospheres, but also used 3D hydrodynamical simulations of stellar atmospheres.
Results: We measured carbon in six of the seven stars: all are carbon-enhanced and belong to the low-carbon band, defined in the TOPoS II paper. We measured lithium (A(Li) = 1.9) in the most iron-poor star (SDSS J1035+0641, [Fe/H] <-5.2). We were also able to measure Li in three stars at [Fe/H] -4.0, two of which lie on the Spite plateau. We confirm that SDSS J1349+1407 is extremely rich in Mg, but not in Ca. It is also very rich in Na. Several of our stars are characterised by low α-to-iron ratios.
Conclusions: The lack of high-carbon band stars at low metallicity can be understood in terms of evolutionary timescales of binary systems. The detection of Li in SDSS J1035+0641 places a strong constraint on theories that aim at solving the cosmological lithium problem. The Li abundance of the two warmer stars at [Fe/H] -4.0 places them on the Spite plateau, while the third, cooler star, lies below. We argue that this suggests that the temperature at which Li depletion begins increases with decreasing [Fe/H]. SDSS J1349+1407 may belong to a class of Mg-rich EMP stars. We cannot assess if there is a scatter in α-to-iron ratios among the EMP stars or if there are several discrete populations. However, the existence of stars with low α-to-iron ratios is supported by our observations.

Based on observations obtained at ESO Paranal Observatory, Programmes 189.D-0165,090.D-0306, 093.D-0136, and 096.D-0468. Title: Using the CIFIST grid of CO5BOLD 3D model atmospheres to study the effects of stellar granulation on photometric colours. I. Grids of 3D corrections in the UBVRI, 2MASS, HIPPARCOS, Gaia, and SDSS systems Authors: Bonifacio, P.; Caffau, E.; Ludwig, H. -G.; Steffen, M.; Castelli, F.; Gallagher, A. J.; Kučinskas, A.; Prakapavičius, D.; Cayrel, R.; Freytag, B.; Plez, B.; Homeier, D. Bibcode: 2018A&A...611A..68B Altcode: 2017arXiv171200024B Context. The atmospheres of cool stars are temporally and spatially inhomogeneous due to the effects of convection. The influence of this inhomogeneity, referred to as granulation, on colours has never been investigated over a large range of effective temperatures and gravities. Aim. We aim to study, in a quantitative way, the impact of granulation on colours.
Methods: We use the CIFIST (Cosmological Impact of the FIrst Stars) grid of CO5BOLD (COnservative COde for the COmputation of COmpressible COnvection in a BOx of L Dimensions, L = 2, 3) hydrodynamical models to compute emerging fluxes. These in turn are used to compute theoretical colours in the UBV RI, 2MASS, HIPPARCOS, Gaia and SDSS systems. Every CO5BOLD model has a corresponding one dimensional (1D) plane-parallel LHD (Lagrangian HydroDynamics) model computed for the same atmospheric parameters, which we used to define a "3D correction" that can be applied to colours computed from fluxes computed from any 1D model atmosphere code. As an example, we illustrate these corrections applied to colours computed from ATLAS models.
Results: The 3D corrections on colours are generally small, of the order of a few hundredths of a magnitude, yet they are far from negligible. We find that ignoring granulation effects can lead to underestimation of Teff by up to 200 K and overestimation of gravity by up to 0.5 dex, when using colours as diagnostics. We have identified a major shortcoming in how scattering is treated in the current version of the CIFIST grid, which could lead to offsets of the order 0.01 mag, especially for colours involving blue and UV bands. We have investigated the Gaia and HIPPARCOS photometric systems and found that the (G - Hp), (BP - RP) diagram is immune to the effects of granulation. In addition, we point to the potential of the RVS photometry as a metallicity diagnostic.
Conclusions: Our investigation shows that the effects of granulation should not be neglected if one wants to use colours as diagnostics of the stellar parameters of F, G, K stars. A limitation is that scattering is treated as true absorption in our current computations, thus our 3D corrections are likely an upper limit to the true effect. We are already computing the next generation of the CIFIST grid, using an approximate treatment of scattering.

The appendix tables are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/611/A68 Title: VizieR Online Data Catalog: 3D correction in 5 photometric systems (Bonifacio+, 2018) Authors: Bonifacio, P.; Caffau, E.; Ludwig, H. -G.; Steffen, M.; Castelli, F.; Gallagher, A. J.; Kucinskas, A.; Prakapavicius, D.; Cayrel, R.; Freytag, B.; Plez, B.; Homeier, D. Bibcode: 2018yCat..36110068B Altcode: We have used the CIFIST grid of CO5BOLD models to investigate the effects of granulation on fluxes and colours of stars of spectral type F, G, and K.

We publish tables with 3D corrections that can be applied to colours computed from any 1D model atmosphere. For Teff>=5000K, the corrections are smooth enough, as a function of atmospheric parameters, that it is possible to interpolate the corrections between grid points; thus the coarseness of the CIFIST grid should not be a major limitation. However at the cool end there are still far too few models to allow a reliable interpolation.

(20 data files). Title: Using CO5BOLD models to predict the effects of granulation on colours . Authors: Bonifacio, P.; Caffau, E.; Ludwig, H. -G.; Steffen, M.; Castelli, F.; Gallagher, A. J.; Prakapavičius, D.; Kučinskas, A.; Cayrel, R.; Freytag, B.; Plez, B.; Homeier, D. Bibcode: 2017MmSAI..88...90B Altcode: In order to investigate the effects of granulation on fluxes and colours, we computed the emerging fluxes from the models in the CO5BOLD grid with metallicities [M/H]=0.0,-1.0,-2.0 and -3.0. These fluxes have been used to compute colours in different photometric systems. We explain here how our computations have been performed and provide some results. Title: TOPoS. III. An ultra iron-poor multiple CEMP system Authors: Caffau, E.; Bonifacio, P.; Spite, M.; Spite, F.; Monaco, L.; Sbordone, L.; François, P.; Gallagher, A. J.; Plez, B.; Zaggia, S.; Ludwig, H. -G.; Cayrel, R.; Koch, A.; Steffen, M.; Salvadori, S.; Klessen, R.; Glover, S.; Christlieb, N. Bibcode: 2016A&A...595L...6C Altcode: 2016arXiv161004106C
Aims: One of the primary objectives of the TOPoS survey is to search for the most metal-poor stars. Our search has led to the discovery of one of the most iron-poor objects known, SDSS J092912.32+023817.0. This object is a multiple system, in which two components are clearly detected in the spectrum.
Methods: We have analysed 16 high-resolution spectra obtained using the UVES spectrograph at the ESO 8.2 m VLT telescope to measure radial velocities and determine the chemical composition of the system.
Results: Cross correlation of the spectra with a synthetic template yields a double-peaked cross-correlation function (CCF) for eight spectra, and in one case there is evidence for the presence of a third peak. Chemical analysis of the spectrum obtained by averaging all the spectra for which the CCF showed a single peak found that the iron abundance is [Fe/H] = -4.97. The system is also carbon enhanced with [C/Fe] = +3.91 (A(C) = 7.44). From the permitted oxygen triplet we determined an upper limit for oxygen of [O/Fe] < +3.52 such that C/O > 1.3. We are also able to provide more stringent upper limits on the Sr and Ba abundances ([Sr/Fe] < +0.70, and [Ba/Fe] < +1.46, respectively).

Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 094.D-0488 and 096.D-0616. Title: HST/STIS abundances in the uranium rich metal poor star CS 31082-001: Constraints on the r-Process Authors: Siqueira-Mello, C.; Spite, M.; Barbuy, B.; Spite, F.; Caffau, E.; Hill, V.; Wanajo, S.; Primas, F.; Plez, B.; Cayrel, R.; Andersen, J.; Nordström, B.; Sneden, C.; Beers, T. C.; Bonifacio, P.; François, P.; Molaro, P. Bibcode: 2016JPhCS.665a2056S Altcode: As a brief revision, the origin of heavy elements and the role of abundances in extremely metal-poor (EMP) stars are presented. Heavy element abundances in the EMP uranium-rich star CS 31082-001 based mainly on near-UV spectra from STIS/HST are presented. These results should be useful for a better characterisation of the neutron exposure(s) that produced the r-process elements in this star, as well as a guide for improving nuclear data and astrophysical site modelling, given that the new element abundances not available in previous works (Ge, Mo, Lu, Ta, W, Re, Pt, Au, and Bi) make CS 31082-001 the most completely well studied r-II object, with a total of 37 detections of n-capture elements. Title: The photospheric solar oxygen project. IV. 3D-NLTE investigation of the 777 nm triplet lines Authors: Steffen, M.; Prakapavičius, D.; Caffau, E.; Ludwig, H. -G.; Bonifacio, P.; Cayrel, R.; Kučinskas, A.; Livingston, W. C. Bibcode: 2015A&A...583A..57S Altcode: 2015arXiv150803487S Context. The solar photospheric oxygen abundance is still widely debated. Adopting the solar chemical composition based on the "low" oxygen abundance, as determined with the use of three-dimensional (3D) hydrodynamical model atmospheres, results in a well-known mismatch between theoretical solar models and helioseismic measurements that is so far unresolved.
Aims: We carry out an independent redetermination of the solar oxygen abundance by investigating the center-to-limb variation of the O i IR triplet lines at 777 nm in different sets of spectra.
Methods: The high-resolution and high signal-to-noise solar center-to-limb spectra are analyzed with the help of detailed synthetic line profiles based on 3D hydrodynamical CO5BOLD model atmospheres and 3D non-LTE line formation calculations with NLTE3D. The idea is to exploit the information contained in the observations at different limb angles to simultaneously derive the oxygen abundance, A(O), and the scaling factor SH that describes the cross-sections for inelastic collisions with neutral hydrogen relative to the classical Drawin formula. Using the same codes and methods, we compare our 3D results with those obtained from the semi-empirical Holweger-Müller model atmosphere as well as from different one-dimensional (1D) reference models.
Results: With the CO5BOLD 3D solar model, the best fit of the center-to-limb variation of the triplet lines is obtained when the collisions by neutral hydrogen atoms are assumed to be efficient, i.e., when the scaling factor SH is between 1.2 and 1.8, depending on the choice of the observed spectrum and the triplet component used in the analysis. The line profile fits achieved with standard 1D model atmospheres (with fixed microturbulence, independent of disk position μ) are clearly of inferior quality compared to the 3D case, and give the best match to the observations when ignoring collisions with neutral hydrogen (SH = 0). The results derived with the Holweger-Müller model are intermediate between 3D and standard 1D.
Conclusions: The analysis of various observations of the triplet lines with different methods yields oxygen abundance values (on a logarithmic scale where A(H) = 12) that fall in the range 8.74 <A(O) < 8.78, and our best estimate of the 3D non-LTE solar oxygen abundance is A(O) = 8.76 ± 0.02. All 1D non-LTE models give much lower oxygen abundances, by up to -0.15 dex. This is mainly a consequence of the assumption of a μ-independent microturbulence. An independent determination of the relevant collisional cross-sections is essential to substantially improve the accuracy of the oxygen abundance derived from the O i IR triplet.

Appendices E and F are available in electronic form at http://www.aanda.org Title: TOPoS . II. On the bimodality of carbon abundance in CEMP stars Implications on the early chemical evolution of galaxies Authors: Bonifacio, P.; Caffau, E.; Spite, M.; Limongi, M.; Chieffi, A.; Klessen, R. S.; François, P.; Molaro, P.; Ludwig, H. -G.; Zaggia, S.; Spite, F.; Plez, B.; Cayrel, R.; Christlieb, N.; Clark, P. C.; Glover, S. C. O.; Hammer, F.; Koch, A.; Monaco, L.; Sbordone, L.; Steffen, M. Bibcode: 2015A&A...579A..28B Altcode: 2015arXiv150405963B Context. In the course of the Turn Off Primordial Stars (TOPoS) survey, aimed at discovering the lowest metallicity stars, we have found several carbon-enhanced metal-poor (CEMP) stars. These stars are very common among the stars of extremely low metallicity and provide important clues to the star formation processes. We here present our analysis of six CEMP stars.
Aims: We want to provide the most complete chemical inventory for these six stars in order to constrain the nucleosynthesis processes responsible for the abundance patterns.
Methods: We analyse both X-Shooter and UVES spectra acquired at the VLT. We used a traditional abundance analysis based on OSMARCS 1D local thermodynamic equilibrium (LTE) model atmospheres and the turbospectrum line formation code.
Results: Calcium and carbon are the only elements that can be measured in all six stars. The range is -5.0 ≤ [Ca/H] <-2.1 and 7.12 ≤ A(C) ≤ 8.65. For star SDSS J1742+2531 we were able to detect three Fe i lines from which we deduced [Fe/H] = -4.80, from four Ca ii lines we derived [Ca/H] = -4.56, and from synthesis of the G-band we derived A(C) = 7.26. For SDSS J1035+0641 we were not able to detect any iron lines, yet we could place a robust (3σ) upper limit of [Fe/H] < -5.0 and measure the Ca abundance, with [Ca/H] = -5.0, and carbon, A(C) = 6.90, suggesting that this star could be even more metal-poor than SDSS J1742+2531. This makes these two stars the seventh and eighth stars known so far with [Fe/H] < -4.5, usually termed ultra-iron-poor (UIP) stars. No lithium is detected in the spectrum of SDSS J1742+2531 or SDSS J1035+0641, which implies a robust upper limit of A(Li) < 1.8 for both stars.
Conclusions: Our measured carbon abundances confirm the bimodal distribution of carbon in CEMP stars, identifying a high-carbon band and a low-carbon band. We propose an interpretation of this bimodality according to which the stars on the high-carbon band are the result of mass transfer from an AGB companion, while the stars on the low-carbon band are genuine fossil records of a gas cloud that has also been enriched by a faint supernova (SN) providing carbon and the lighter elements. The abundance pattern of the UIP stars shows a large star-to-star scatter in the [X/Ca] ratios for all elements up to aluminium (up to 1 dex), but this scatter drops for heavier elements and is at most of the order of a factor of two. We propose that this can be explained if these stars are formed from gas that has been chemically enriched by several SNe, that produce the roughly constant [X/Ca] ratios for the heavier elements, and in some cases the gas has also been polluted by the ejecta of a faint SN that contributes the lighter elements in variable amounts. The absence of lithium in four of the five known unevolved UIP stars can be explained by a dominant role of fragmentation in the formation of these stars. This would result either in a destruction of lithium in the pre-main-sequence phase, through rotational mixing or to a lack of late accretion from a reservoir of fresh gas. The phenomenon should have varying degrees of efficiency.

Based on observations obtained at ESO Paranal Observatory, programme 091.D-0288, 091.D-0305, 189.D-0165.Appendix A is available in electronic form at http://www.aanda.orgTables 4 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/579/A28 Title: VizieR Online Data Catalog: Abundances of 3 CEMP stars (Bonifacio+, 2015) Authors: Bonifacio, P.; Caffau, E.; Spite, M.; Limongi, M.; Chieffi, A.; Klessen, R. S.; Francois, P.; Molaro, P.; Ludwig, H. -G.; Zaggia, S.; Spite, F.; Plez, B.; Cayrel, R.; Christlieb, N.; Clark, P. C.; Glover, S. C. O.; Hammer, F.; Koch, A.; Monaco, L.; Sbordone, L.; Steffen, M. Bibcode: 2015yCat..35790028B Altcode: We analyse both X-Shooter and UVES spectra acquired at the VLT. We used a traditional abundance analysis based on OSMARCS 1D Local Thermodynamic Equilibrium (LTE) model atmospheres and the TURBOSPECTRUM line formation code.

(2 data files). Title: High-resolution abundance analysis of very metal-poor r-I stars Authors: Siqueira Mello, C.; Hill, V.; Barbuy, B.; Spite, M.; Spite, F.; Beers, T. C.; Caffau, E.; Bonifacio, P.; Cayrel, R.; François, P.; Schatz, H.; Wanajo, S. Bibcode: 2014A&A...565A..93S Altcode: 2014arXiv1404.0234S Context. Moderately r-process-enriched stars (r-I; +0.3 ≤ [Eu/Fe] ≤ +1.0) are at least four times as common as those that are greatly enriched in r-process elements (r-II; [Eu/Fe] > +1.0), and the abundances in their atmospheres are important tools for obtaining a better understanding of the nucleosynthesis processes responsible for the origin of the elements beyond the iron peak.
Aims: The main aim of this work is to derive abundances for a sample of seven metal-poor stars with -3.4 ≤ [Fe/H] ≤ -2.4 classified as r-I stars, to understand the role of these stars for constraining the astrophysical nucleosynthesis event(s) that is (are) responsible for the production of the r-process, and to investigate whether they differ, in any significant way, from the r-II stars.
Methods: We carried out a detailed abundance analysis based on high-resolution spectra obtained with the VLT/UVES spectrograph, using spectra in the wavelength ranges 3400-4500 Å, 6800-8200 Å, and 8700-10 000 Å, with resolving power R ~ 40 000 (blue arm) and R ~ 55 000 (red arm). The OSMARCS LTE 1D model atmosphere grid was employed, along with the spectrum synthesis code Turbospectrum.
Results: We have derived abundances of the light elements Li, C, and N, the α-elements Mg, Si, S, Ca, and Ti, the odd-Z elements Al, K, and Sc, the iron-peak elements V, Cr, Mn, Fe, Co, and Ni, and the trans-iron elements from the first peak (Sr, Y, Zr, Mo, Ru, and Pd), the second peak (Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb), the third peak (Os and Ir, as upper limits), and the actinides (Th) regions. The results are compared with values for these elements for r-II and "normal" very and extremely metal-poor stars reported in the literature, ages based on radioactive chronometry are explored using different models, and a number of conclusions about the r-process and the r-I stars are presented. Hydrodynamical models were used for some elements, and general behaviors for the 3D corrections were presented. Although the abundance ratios of the second r-process peak elements (usually associated with the main r-process) are nearly identical for r-I and r-II stars, the first r-process peak abundance ratios (probably associated with the weak r-process) are more enhanced in r-I stars than in r-II stars, suggesting that differing nucleosynthesis pathways were followed by stars belonging to these two different classifications.

Observations obtained with the VLT, at the European Southern Observatory, Paranal, Chile, under proposal 080.D-0194(A) (PI:V. Hill).Appendix A is available in electronic form at http://www.aanda.org Title: r-Process abundances in metal-poor Galactic halo stars Authors: Siqueira-Mello, C.; Barbuy, B.; Spite, M.; Spite, F.; Caffau, E.; Hill, V.; Wanajo, S.; François, P.; Bonifacio, P.; Cayrel, R. Bibcode: 2014MmSAI..85..232S Altcode: The site of the r-process is not completely defined, and several models try to explain the origin of the trans-Fe elements. Observed abundances are the best clues to bring some light to this multiplicity of possible mechanisms, and the extremely metal-poor (EMP) Galactic halo stars have a special role in this problem. In this contribution we present the solution of a long-standing problem about the origin of the heavy elements in the metal-poor halo subgiant star HD 140283, and its correlation with the Truran's theory. Next, we describe the results obtained with the EMP r-II star CS 31082-001 in the frame of the ESO Large Program ``First Stars''. Using STIS/HST observations we provide abundances for elements never presented before in this stars, making CS 31082-001 the most complete r-II object studied, with a total of 37 detections of neutron-capture elements. Finally, we present the results obtained from a sample of seven r-I stars, showing how those objects can help us solving the heavy elements problem. Conclusions are also described. Title: Barbier, Daniel Authors: Cayrel, Roger Bibcode: 2014bea..book..160C Altcode: No abstract at ADS Title: Chalonge, Daniel Authors: Cayrel, Roger Bibcode: 2014bea..book..398C Altcode: No abstract at ADS Title: The first generations of stars Authors: Caffau, E.; Gallagher, A.; Bonifacio, P.; Cayrel, R.; Christlieb, N.; Clark, P. C.; Francois, P.; Glover, S.; Klessen, R. S.; Koch, A.; Ludwig, H. G.; Monaco, L.; Plez, B.; Sbordone, L.; Spite, M.; Spite, F.; Steffen, M.; Zaggia, S. Bibcode: 2014nic..confE..53C Altcode: 2014PoS...204E..53C No abstract at ADS Title: TOPoS: chemical study of extremely metal-poor stars. Authors: Caffau, E.; Sbordone, L.; Bonifacio, P.; Cayrel, R.; Christlieb, N.; Clark, P.; François, P.; Glover, S.; Klessen, R.; Koch, A.; Ludwig, H. -G.; Monaco, L.; Plez, B.; Spite, F.; Spite, M.; Steffen, M.; Zaggia, S. Bibcode: 2014MmSAI..85..222C Altcode: The extremely metal-poor (EMP) stars hold in their atmospheres the fossil record of the chemical composition of the early phases of the Galactic evolution. The chemical analysis of such objects provides important constraints on these early phases. EMP stars are very rare objects; to dig them out, large amounts of data have to be processed. With an automatic procedure, we analysed objects with colours of Turn-Off stars from the Sloan Digital Sky Survey to select a sample of good candidate EMP stars. In the latest years, we observed a sample of these candidates with X-Shooter and UVES, and we have an ongoing ESO large programme to use these spectrographs to observe EMP stars. I will report here the results on metallicity and Strontium abundance.

Based on observations obtained at ESO Paranal Observatory, programme 189.D-0165(A) Title: 6Li/7Li isotopic ratio in the most metal-poor binary CS22876-032 Authors: Gonzalez-Hernandez, J.; Caffau, E.; Ludwig, H. G.; Bonifacio, P.; Steffen, M.; Monaco, L.; Cayrel, R. Bibcode: 2014nic..confE..23G Altcode: 2014PoS...204E..23G No abstract at ADS Title: High-Resolution Abundance Analysis of Very Metal-Poor R-I Stars Authors: Siqueira Mello, C.; Hill, V.; Barbuy, B.; Spite, M.; Spite, F.; Beers, T.; Caffau, E.; Bonifacio, P.; Cayrel, R.; Francois, P.; Schatz, H.; Wanajo, S. Bibcode: 2014nic..confE.157S Altcode: 2014PoS...204E.157S No abstract at ADS Title: X-shooter GTO: evidence for a population of extremely metal-poor, alpha-poor stars Authors: Caffau, E.; Bonifacio, P.; François, P.; Sbordone, L.; Spite, M.; Monaco, L.; Plez, B.; Spite, F.; Zaggia, S.; Ludwig, H. -G.; Cayrel, R.; Molaro, P.; Randich, S.; Hammer, F.; Hill, V. Bibcode: 2013A&A...560A..15C Altcode: 2013arXiv1309.4913C Context. The extremely metal-poor stars are the direct descendants of the first generation stars. They carry the chemical signature of the pristine Universe at the time they formed, shortly after the Big Bang.
Aims: We aim to derive information about extremely metal-poor stars from their observed spectra.
Methods: Four extremely metal-poor stars were selected from the Sloan Digital Sky Survey (SDSS) and observed during the guaranteed observing time of X-shooter. The X-shooter spectra were analysed using an automatic code, MyGIsFOS, which is based on a traditional analysis method. It makes use of a synthetic grid computed from one-dimensional, plane-parallel, hydrostatic model atmospheres.
Results: The low metallicity derived from the SDSS spectra is confirmed here. Two kinds of stars are found. Two stars are confirmed to be extremely metal-poor, with no evidence of any enhancement in carbon. The two other stars are strongly enhanced in carbon. We could not derive iron abundance for one of them, while [Ca/H] is below -4.5. Two of the stars are members of the rare population of extremely metal-poor stars low in alpha elements.

Based on observations obtained at ESO Paranal Observatory, GTO programme 089.D-0039. Title: TOPoS. I. Survey design and analysis of the first sample Authors: Caffau, E.; Bonifacio, P.; Sbordone, L.; François, P.; Monaco, L.; Spite, M.; Plez, B.; Cayrel, R.; Christlieb, N.; Clark, P.; Glover, S.; Klessen, R.; Koch, A.; Ludwig, H. -G.; Spite, F.; Steffen, M.; Zaggia, S. Bibcode: 2013A&A...560A..71C Altcode: 2013arXiv1310.6963C Context. The metal-weak tail of the metallicity distribution function (MDF) of the Galactic Halo stars contains crucial information on the formation mode of the first generation of stars. To determine this observationally, it is necessary to observe large numbers of extremely metal-poor stars.
Aims: We present here the Turn-Off Primordial Stars survey (TOPoS) that is conducted as an ESO Large Programme at the VLT. This project has four main goals: (i) to understand the formation of low-mass stars in a low-metallicity gas: determine the metal-weak tail of the halo MDF below [M/H] = -3.5; in particular, we aim at determining the critical metallicity, that is the lowest metallicity sufficient for the formation of low-mass stars; (ii) to determine in extremely metal-poor stars the relative abundances of the elements that are the signature of the massive first stars; (iii) to determine the trend of the lithium abundance at the time when the Galaxy formed; and (iv) to derive the fraction of C-enhanced extremely metal-poor stars with respect to normal extremely metal-poor stars. The large number of stars observed in the SDSS provides a good sample of candidate stars at extremely low metallicity.
Methods: Candidates with turn-off colours down to magnitude g = 20 were selected from the low-resolution spectra of SDSS by means of an automated procedure. X-Shooter has the potential of performing the necessary follow-up spectroscopy, providing accurate metallicities and abundance ratios for several key elements for these stars.
Results: We present here the stellar parameters of the first set of stars. The nineteen stars range in iron abundance between -4.1 and -2.9 dex relative to the Sun. Two stars have a high radial velocity and, according to our estimate of their kinematics, appear to be marginally bound to the Galaxy and are possibly accreted from another galaxy.

Based on observations obtained at ESO Paranal Observatory, GTO programme 189.D-0165(A). Title: First stars. XVI. HST/STIS abundances of heavy elements in the uranium-rich metal-poor star CS 31082-001 Authors: Siqueira Mello, C.; Spite, M.; Barbuy, B.; Spite, F.; Caffau, E.; Hill, V.; Wanajo, S.; Primas, F.; Plez, B.; Cayrel, R.; Andersen, J.; Nordström, B.; Sneden, C.; Beers, T. C.; Bonifacio, P.; François, P.; Molaro, P. Bibcode: 2013A&A...550A.122S Altcode: 2012arXiv1212.0211S Context. The origin and site(s) of the r-process nucleosynthesis is(are) still not known with certainty, but complete, detailed r-element abundances offer our best clues. The few extremely metal-poor (EMP) stars with large r-element excesses allow us to study the r-process signatures in great detail, with minimal interference from later stages of Galactic evolution. CS 31082-001 is an outstanding example of the information that can be gathered from these exceptional stars.
Aims: Here we aim to complement our previous abundance determinations for third-peak r-process elements with new and improved results for elements of the first and second r-process peaks from near-UV HST/STIS and optical UVES spectra. These results should provide new insight into the nucleosynthesis of the elements beyond iron.
Methods: The spectra were analyzed by a consistent approach based on an OSMARCS LTE model atmosphere and the Turbospectrum spectrum synthesis code to derive abundances of heavy elements in CS 31082-001, and using updated oscillator strengths from the recent literature. Synthetic spectra were computed for all lines of the elements of interest to check for proper line intensities and possible blends in these crowded spectra. Our new abundances were combined with the best previous results to provide reliable mean abundances for the first and second-peak r-process elements.
Results: We present new abundances for 23 neutron-capture elements, 6 of which - Ge, Mo, Lu, Ta, W, and Re - have not been reported before. This makes CS 31082-001 the most completely studied r-II star, with abundances for a total of 37 neutron-capture elements. We also present the first NLTE+3D abundance of lead in this star, further constraining the nature of the r-process.

Based on observations made with the NASA/ESA Hubble Space Telescope (HST) through the Space Telescope Science Institute, operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555; and with the ESO Very Large Telescope at Paranal Observatory, Chile; Progr. ID 165.N-0276.Appendix A is available in electronic form at http://www.aanda.org Title: Oxygen spectral line synthesis: 3D non-LTE with CO5BOLD hydrodynamical model atmospheres. Authors: Prakapavičius, D.; Steffen, M.; Kučinskas, A.; Ludwig, H. -G.; Freytag, B.; Caffau, E.; Cayrel, R. Bibcode: 2013MSAIS..24..111P Altcode: 2013arXiv1303.2016P In this work we present first results of our current project aimed at combining the 3D hydrodynamical stellar atmosphere approach with non-LTE (NLTE) spectral line synthesis for a number of key chemical species. We carried out a full 3D-NLTE spectrum synthesis of the oxygen IR 777 nm triplet, using a modified and improved version of our NLTE3D package to calculate departure coefficients for the atomic levels of oxygen in a CO5BOLD 3D hydrodynamical solar model atmosphere. Spectral line synthesis was subsequently performed with the Linfor3D code. In agreement with previous studies, we find that the lines of the oxygen triplet produce deeper cores under NLTE conditions, due to the diminished line source function in the line forming region. This means that the solar oxygen IR 777 nm lines should be stronger in NLTE, leading to negative 3D NLTE-LTE abundance corrections. Qualitatively this result would support previous claims for a relatively low solar oxygen abundance. Finally, we outline several further steps that need to be taken in order to improve the physical realism and numerical accuracy of our current 3D-NLTE calculations. Title: r-process abundances in the EMP star CS 31082-001 using STIS/HST Authors: Siqueira-Mello, C., Jr.; Spite, M.; Barbuy, B.; Spite, F.; Caffau, E.; Hill, V.; Wanajo, S.; Primas, F.; Plez, B.; Cayrel, R.; Andersen, J.; Nordström, B.; Sneden, C.; Beers, T. C.; Bonifacio, P.; François, P.; Molaro, P. Bibcode: 2012sf2a.conf..129S Altcode: We present a brief revision of the origin of heavy elements and the role of abundances in extremely metal-poor (EMP) stars, in providing improved constraints on the nature of the early nucleosynthesis mechanisms. Heavy element abundances in the EMP uranium-rich star CS 31082-001 based mainly on near-UV spectra from STIS/HST are presented. With new abundances for 9 n-elements not available in previous works (Ge, Mo, Lu, Ta, W, Re, Pt, Au, and Bi) this work makes CS 31082-001 the most completely well studied r-II object, with a total of 37 detections of n-capture elements. These results should be useful for a better characterisation of the neutron exposure(s) that produced the r-process elements in this star, as well as a guide for improving nuclear data and astrophysical site modelling. Title: A primordial star in the heart of the Lion Authors: Caffau, E.; Bonifacio, P.; François, P.; Spite, M.; Spite, F.; Zaggia, S.; Ludwig, H. -G.; Steffen, M.; Mashonkina, L.; Monaco, L.; Sbordone, L.; Molaro, P.; Cayrel, R.; Plez, B.; Hill, V.; Hammer, F.; Randich, S. Bibcode: 2012A&A...542A..51C Altcode: 2012arXiv1203.2607C Context. The discovery and chemical analysis of extremely metal-poor stars permit a better understanding of the star formation of the first generation of stars and of the Universe emerging from the Big Bang.
Aims: We report the study of a primordial star situated in the centre of the constellation Leo (SDSS J102915+172927).
Methods: The star, selected from the low-resolution spectrum of the Sloan Digital Sky Survey, was observed at intermediate (with X-Shooter at VLT) and at high spectral resolution (with UVES at VLT). The stellar parameters were derived from the photometry. The standard spectroscopic analysis based on 1D ATLAS models was completed by applying 3D and non-LTE corrections.
Results: An iron abundance of [Fe/H ] = -4.89 makes SDSS J102915+172927 one of the lowest [Fe/H] stars known. However, the absence of measurable C and N enhancements indicates that it has the lowest metallicity, Z ≤ 7.40 × 10-7 (metal-mass fraction), ever detected. No oxygen measurement was possible.
Conclusions: The discovery of SDSS J102915+172927 highlights that low-mass star formation occurred at metallicities lower than previously assumed. Even lower metallicity stars may yet be discovered, with a chemical composition closer to the composition of the primordial gas and of the first supernovae.

Based on observations obtained at ESO Paranal Observatory, GTO programme 086.D-0094 and programme 286.D-5045. Title: NLTE determination of the calcium abundance and 3D corrections in extremely metal-poor stars Authors: Spite, M.; Andrievsky, S. M.; Spite, F.; Caffau, E.; Korotin, S. A.; Bonifacio, P.; Ludwig, H. -G.; François, P.; Cayrel, R. Bibcode: 2012A&A...541A.143S Altcode: 2012arXiv1204.1139S Context. Calcium is a key element for constraining the models of chemical enrichment of the Galaxy.
Aims: Extremely metal-poor stars contain the fossil records of the chemical composition of the early Galaxy and it is important to compare Ca abundance with abundances of other light elements, that are supposed to be synthesized in the same stellar evolution phases.
Methods: The NLTE profiles of the calcium lines were computed in a sample of 53 extremely metal-poor stars with a modified version of the program MULTI, which allows a very good description of the radiation field.
Results: With our new model atom we are able to reconcile the abundance of Ca deduced from the Ca I and Ca II lines in Procyon. This abundance is found to be solar. We find that [Ca/Fe] = 0.50±0.09 in the early Galaxy, a value slightly higher than the previous LTE estimations. The scatter of the ratios [X/Ca] is generally smaller than the scatter of the ratio [X/Mg] where X is a "light metal" (O, Na, Mg, Al, S, and K) with the exception of Al. These scatters cannot be explained by error of measurements, except for oxygen. Surprisingly, the scatter of [X/Fe] is always equal to, or even smaller than, the scatter around the mean value of [X/Ca]. We note that at low metallicity, the wavelength of the Ca I resonance line is shifted relative to the (weaker) subordinate lines, a signature of the effect of convection. The Ca abundance deduced from the Ca I resonance line (422.7 nm) is found to be systematically smaller at very low metallicity than the abundance deduced from the subordinate lines. Our computations of the effects of convection (3D effects) are not able to explain this difference. A fully consistent 3D NLTE model atmosphere and line formation scheme would be necessary to fully capture the physics of the stellar atmosphere.

Based on observations obtained with the ESO Very Large Telescope at Paranal Observatory, Chile (Large Programme "First Stars", ID 165.N-0276(A); P.I.: R. Cayrel).The NLTE corrections of the Ca lines are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/541/A143 Title: VizieR Online Data Catalog: NLTE Corrections of the Ca lines (Spite+, 2012) Authors: Spite, M.; Andrievsky, S. M.; Spite, F.; Caffau, E.; Korotin, S. A.; Bonifacio, P.; Ludwig, H. -G.; Francois, P.; Cayrel, R. Bibcode: 2012yCat..35410143S Altcode: 2012yCat..35419143S The NLTE corrections were computed for 51 CaI lines and 16 CaII lines for a grid of models with different metallicities from [Fe/H]=0.0 to [Fe/H]=-3. These corrections must be added to the LTE value of [Ca/H], they were computed only if the equivalent width of the Ca line was stronger than 3mÅ. In the tables the model is given in the form (Teff, logg, [Fe/H], [Ca/Fe]) where Teff is the effective temperature, and logg the logarithm of the surface gravity)

(5 data files). Title: 6Li detection in metal-poor stars: can 3D model atmospheres solve the second lithium problem? Authors: Steffen, M.; Cayrel, R.; Caffau, E.; Bonifacio, P.; Ludwig, H. -G.; Spite, M. Bibcode: 2012MSAIS..22..152S Altcode: 2012arXiv1206.2239S The presence of 6Li in the atmospheres of metal-poor halo stars is usually inferred from the detection of a subtle extra depression in the red wing of the 7Li doublet line at 670.8 nm. However, as pointed out recently by \cite{Cayrel2007}, the intrinsic line asymmetry caused by convective flows in the photospheres of cool stars is almost indistinguishable from the asymmetry produced by a weak 6Li blend on a (presumed) symmetric 7Li profile. Previous determinations of the 6Li/ 7Li isotopic ratio based on 1D model atmospheres, ignoring the convection-induced line asymmetry, must therefore be considered as upper limits. By comparing synthetic 1D LTE and 3D non-LTE line profiles of the iLi 670.8 nm feature, we quantify the differential effect of the convective line asymmetry on the derived 6Li abundance as a function of effective temperature, gravity, and metallicity. As expected, we find that the asymmetry effect systematically reduces the resulting 6Li/7Li ratios. Depending on the stellar parameters, the 3D-1D offset in 6Li/7Li ranges between -0.005 and -0.020. When this purely theoretical correction is taken into account for the \cite{A2006} sample of stars, the number of significant 6Li detections decreases from 9 to 5 (2sigma criterion), or from 5 to 2 (3sigma criterion).

We also present preliminary results of a re-analysis of high-resolution, high S/N spectra of individual metal-poor turn-off stars, to see whether the second Lithium problem actually disappears when accounting properly for convection and non-LTE line formation in 3D stellar atmospheres. Out of 8 stars, HD 84937 seems to be the only significant (2sigma ) detection of 6Li. In view of our results, the existence of a 6Li plateau appears questionable. Title: Preliminary determination of the Non-LTE Calcium abundance in a sample of extremely metal-poor stars* Authors: Spite, M.; Spite, F.; Bonifacio, P.; Caffau, E.; Andrievsky, S.; Korotin, S.; Cayrel, R.; François, P. Bibcode: 2011sf2a.conf..353S Altcode: The abundance ratios of the elements found in the extremely metal-poor stars (EMP) are a test of the yields predicted by the models of supernovae. For precise comparisons, it is of course preferable to avoid the approximation of LTE. The difference of LTE and NLTE profiles is displayed for three strong lines. The NLTE abundances of Ca are derived from the profiles of about 15 Ca I lines in the EMP giants and about 10 lines in the turnoff stars. The improved abundance trends are consistent with a [Ca/Fe] ratio constant vs. [Fe/H], and with a [Ca/Mg] ratio slightly declining when [Mg/H] increases. Also [Ca/Mg] presents a scatter larger than [Ca/Fe]. As far as the comparison with sulfur (another alpha elment) is concerned we find that [S/Ca] presents a scatter smaller than [S/Mg]. Title: The Hα Balmer line as an effective temperature criterion Authors: Cayrel, R.; van't Veer-Menneret, C.; Allard, N. F.; Stehlé, C. Bibcode: 2011sf2a.conf..267C Altcode: For eleven stars with an accurate effective temperature derived from their apparent angular diameter we determine the effective temperature of the Kurucz Atlas9 model that provides the best fit of the computed theoretical Hα profile (using the recent theoretical advances) with the corresponding observed profile, extracted from the S4N spectroscopic database. The two sets of effective temperatures have a significant offset, but are tightly correlated, with a correlation coefficient of 0.9976. The regression straight line of T_{eff}(direct) versus T_{eff}(Hα) enables us to reach the true effective temperature from the spectroscopic observation of the Hα profile, with an rms error of only 30 K. This provides a way of obtaining the true effective temperature of a reddened star. Title: X-shooter Finds an Extremely Primitive Star Authors: Caffau, E.; Bonifacio, P.; François, P.; Sbordone, L.; Monaco, L.; Spite, M.; Spite, F.; Ludwig, H. -G.; Cayrel, R.; Zaggia, S.; Hammer, F.; Randich, S.; Molaro, P.; Hill, V. Bibcode: 2011Msngr.146...28C Altcode: Low-mass extremely metal-poor (EMP) stars hold the fossil record of the chemical composition of the early phases of the Universe in their atmospheres. Chemical analysis of such objects provides important constraints on these early phases. EMP stars are rather rare objects: to dig them out, large amounts of data have to be considered. We have analysed stars from the Sloan Digital Sky Survey using an automatic procedure and selected a sample of good candidate EMP stars, which we observed with the spectrographs X-shooter and UVES. We could confirm the low metallicity of our sample of stars, and we succeeded in finding a record metal-poor star. Title: X-Shooter GTO: chemical analysis of a sample of EMP candidates Authors: Caffau, E.; Bonifacio, P.; François, P.; Spite, M.; Spite, F.; Zaggia, S.; Ludwig, H. -G.; Monaco, L.; Sbordone, L.; Cayrel, R.; Hammer, F.; Randich, S.; Hill, V.; Molaro, P. Bibcode: 2011A&A...534A...4C Altcode: 2011arXiv1109.0992C Context. Extremely metal-poor stars (EMP) are very rare objects that hold in their atmospheres the fossil record of the chemical composition of the early phases of Galactic evolution. Finding these objects and determining their chemical composition provides important constraints on these early phases.
Aims: Using a carefully designed selection method, we chose a sample of candidate EMP stars from the low resolution spectra of the Sloan Digital Sky Survey and observed them with X-Shooter at the VLT to confirm their metallicities and determine abundances for as many elements as possible.
Methods: The X-Shooter spectra are analysed by means of one-dimensional, plane-parallel, hydrostatic model atmospheres. Corrections for the granulation effects are computed using CO5BOLD hydrodynamical simulations.
Results: All the candidates are confirmed to be EMP stars, proving the efficiency of our selection method within about 0.5 dex. The chemical composition of this sample is compatible with those of brighter samples, suggesting that the stars in the Galactic halo are well mixed.
Conclusions: These observations show that it is feasible to observe, in a limited amount of time, a large sample of about one hundred stars among EMP candidates selected from the SDSS. Such a size of sample will allow us, in particular, to confirm or refute the existence of a vertical drop in the Galactic halo metallicity distribution function around [Fe/H] ~ -3.5.

Based on observations obtained at ESO Paranal Observatory, GTO programme 086.D-0094. Title: First stars. XV. Third-peak r-process element and actinide abundances in the uranium-rich star CS31082-001 Authors: Barbuy, B.; Spite, M.; Hill, V.; Primas, F.; Plez, B.; Cayrel, R.; Spite, F.; Wanajo, S.; Siqueira Mello, C.; Andersen, J.; Nordström, B.; Beers, T. C.; Bonifacio, P.; François, P.; Molaro, P. Bibcode: 2011A&A...534A..60B Altcode: Context. A small fraction of extremely metal-poor (EMP) stars exhibit moderate to extreme excesses of heavy neutron-capture elements produced in the r-process. The production site(s) of these elements in the early Galaxy remain(s) unclear, as is the reason for their occasional enhancement in the otherwise regular pattern of abundances of elements up to the iron peak. The detailed abundance pattern of the heaviest elements in EMP stars provides insight into their origin and role in the chemical enrichment of the early Galaxy and in radioactive nucleochronology.
Aims: The EMP giant star CS 31082-001 ([Fe/H] ~ -2.9) exhibits an extreme enhancement of neutron-capture elements ([r/Fe] ~ +1.7) with U and Th enhanced by a further ~+0.7 dex, and a minimum of blending by molecular lines such as CH or CN. A rich inventory of r-process element abundances was established previously from optical spectra. Here we aim to supplement these data with abundances from near-UV spectroscopy of the third-peak neutron-capture elements, which are crucial for understanding the synthesis of the heaviest elements.
Methods: Near-UV spectra from HST/STIS were analysed with LTE model atmospheres and spectrum synthesis calculations to derive new abundances of Os, Ir, Pt, Au, Bi and Pb in CS 31082-001.
Results: Together with earlier data, the resulting abundance pattern for the r-process elements provides improved constraints on the nature of the r-process. The observed U and Th abundances and the initial production ratio place CS 31082-001 as one of the oldest stars in the Galaxy, consistent with its extreme metal deficiency. Comparison with the heaviest stable reference elements and with the daughter nuclides Pb and Bi provides a consistency check on this age determination. Finally, the existence of such r-element rich stars indicate that the early chemical evolution of the Galaxy was localised and inhomogeneous.

Based on observations made with the NASA/ESA Hubble Space Telescope (HST) through the Space Telescope Science Institute, operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555; and with the ESO Very Large Telescope at Paranal Observatory, Chile; Progr. ID 165.N-0276. Title: An extremely primitive star in the Galactic halo Authors: Caffau, Elisabetta; Bonifacio, Piercarlo; François, Patrick; Sbordone, Luca; Monaco, Lorenzo; Spite, Monique; Spite, François; Ludwig, Hans-G.; Cayrel, Roger; Zaggia, Simone; Hammer, François; Randich, Sofia; Molaro, Paolo; Hill, Vanessa Bibcode: 2011Natur.477...67C Altcode: 2012arXiv1203.2612C The early Universe had a chemical composition consisting of hydrogen, helium and traces of lithium; almost all other elements were subsequently created in stars and supernovae. The mass fraction of elements more massive than helium, Z, is known as `metallicity'. A number of very metal-poor stars has been found, some of which have a low iron abundance but are rich in carbon, nitrogen and oxygen. For theoretical reasons and because of an observed absence of stars with Z<1.5×10-5, it has been suggested that low-mass stars cannot form from the primitive interstellar medium until it has been enriched above a critical value of Z, estimated to lie in the range 1.5×10-8 to 1.5×10-6 (ref. 8), although competing theories claiming the contrary do exist. (We use `low-mass' here to mean a stellar mass of less than 0.8 solar masses, the stars that survive to the present day.) Here we report the chemical composition of a star in the Galactic halo with a very low Z (<=6.9×10-7, which is 4.5×10-5 times that of the Sun) and a chemical pattern typical of classical extremely metal-poor stars--that is, without enrichment of carbon, nitrogen and oxygen. This shows that low-mass stars can be formed at very low metallicity, that is, below the critical value of Z. Lithium is not detected, suggesting a low-metallicity extension of the previously observed trend in lithium depletion. Such lithium depletion implies that the stellar material must have experienced temperatures above two million kelvin in its history, given that this is necessary to destroy lithium. Title: The Hα Balmer line as an effective temperature criterion. I. Calibration using 1D model stellar atmospheres Authors: Cayrel, R.; van't Veer-Menneret, C.; Allard, N. F.; Stehlé, C. Bibcode: 2011A&A...531A..83C Altcode:
Aims: We attempt to derive the true effective temperature of a star from the spectroscopic observation of its Hα Balmer line profile.
Methods: The method is possible thanks to advances in two respects. First there have been progresses in the theoretical treatment of the broadening mechanisms of Hα. Second, there has been a rapid increase in the number of stars with an apparent diameter measured with an accuracy of the order of 1 percent, enabling us to obtain an accurate effective temperature Teff for a dozen of stars using the direct method by means of combining the apparent diameter and the bolometric flux.
Results: For the eleven stars with an accurate effective temperature derived from their apparent angular diameter we determined the effective temperature of the Kurucz Atlas9 model that provides the best fit of the computed theoretical Hα profile (using the recent theoretical advances) with the corresponding observed profile, extracted from the S4N spectroscopic database. The two sets of effective temperatures have a significant offset, but are tightly correlated, with a correlation coefficient of 0.9976. The regression straight line of Teff(direct) versus Teff(Hα) enables us to reach the true effective temperature from the spectroscopic observation of the Hα profile, with an rms error of only 30 K. This provides a way of obtaining the true effective temperature of a reddened star.
Conclusions: We succeeded in obtaining empirically the true stellar effective temperature from Hα profile using Kurucz's Atlas9 grid of 1D model atmospheres. Full understanding of the difference between Teff(direct) and Teff(Hα) would require a 3D approach, with radiative hydrodynamical models, which will be the subject of a future paper. Title: NLTE strontium abundance in a sample of extremely metal poor stars and the Sr/Ba ratio in the early Galaxy Authors: Andrievsky, S. M.; Spite, F.; Korotin, S. A.; François, P.; Spite, M.; Bonifacio, P.; Cayrel, R.; Hill, V. Bibcode: 2011A&A...530A.105A Altcode: 2011arXiv1104.0476A Context. Heavy element abundances in extremely metal-poor stars provide strong constraints on the processes of forming these elements in the first stars.
Aims: We attempt to determine precise abundances of strontium in a homogeneous sample of extremely metal-poor stars.
Methods: The abundance of strontium in 54 very or extremely metal-poor stars, was redetermined by abandoning the local thermodynamic equilibrium (LTE) hypothesis, and fitting non-LTE (NLTE) profiles to the observed spectral lines. The corrected Sr abundances and previously obtained NLTE Ba abundances are compared to the predictions of several hypothetical formation processes for the lighter neutron-capture elements.
Results: Our NLTE abundances confirm the previously determined huge scatter of the strontium abundance in low metallicity stars. This scatter is also found (and is even larger) at very low metallicities (i.e. early in the chemical evolution). The Sr abundance in the extremely metal-poor (EMP) stars is compatible with the main r-process involved in other processes (or by variations of the r-process), as we briefly discuss. Title: Lines of heavy elements and Feiiin the UV of CS 31082-001 Authors: Barbuy, B.; Siqueira Mello, C., Jr.; Spite, M.; Spite, F.; Bonifacio, P.; Hill, V.; Primas, F.; Plez, B.; Cayrel, R.; François, P.; Sneden, C.; Beers, T. C.; Andersen, J.; Nordström, B.; Molaro, P. Bibcode: 2011CaJPh..89..357B Altcode: No abstract at ADS Title: First stars. XIV. Sulfur abundances in extremely metal-poor stars Authors: Spite, M.; Caffau, E.; Andrievsky, S. M.; Korotin, S. A.; Depagne, E.; Spite, F.; Bonifacio, P.; Ludwig, H. -G.; Cayrel, R.; François, P.; Hill, V.; Plez, B.; Andersen, J.; Barbuy, B.; Beers, T. C.; Molaro, P.; Nordström, B.; Primas, F. Bibcode: 2011A&A...528A...9S Altcode: 2010arXiv1012.4358S Context. Precise S abundances are important in the study of the early chemical evolution of the Galaxy. In particular the site of the formation remains uncertain because, at low metallicity, the trend of this α-element versus [Fe/H] remains unclear. Moreover, although sulfur is not bound significantly in dust grains in the ISM, it seems to behave differently in DLAs and old metal-poor stars.
Aims: We attempt a precise measurement of the S abundance in a sample of extremely metal-poor stars observed with the ESO VLT equipped with UVES, taking into account NLTE and 3D effects.
Methods: The NLTE profiles of the lines of multiplet 1 of S I were computed with a version of the program MULTI, including opacity sources from ATLAS9 and based on a new model atom for S. These profiles were fitted to the observed spectra.
Results: We find that sulfur in EMP stars behaves like the other α-elements, with [S/Fe] remaining approximately constant below [Fe/H] = -3. However, [S/Mg] seems to decrease slightly with increasing [Mg/H]. The overall abundance patterns of O, Na, Mg, Al, S, and K are most closely matched by the SN model yields by Heger & Woosley. The [S/Zn] ratio in EMP stars is solar, as also found in DLAs. We derive an upper limit to the sulfur abundance [S/Fe] < +0.5 for the ultra metal-poor star CS 22949-037. This, along with a previously reported measurement of zinc, argues against the conjecture that the light-element abundance pattern of this star (and by analogy, the hyper iron-poor stars HE 0107-5240 and HE 1327-2326) would be due to dust depletion.

Based on observations obtained with the ESO Very Large Telescope at Paranal (Large Programme "First Stars", ID 165, N-0276, P.I.: Cayrel. Title: Extremely metal-poor stars in SDSS fields Authors: Bonifacio, P.; Caffau, E.; François, P.; Sbordone, L.; Ludwig, H. -G.; Spite, M.; Molaro, P.; Spite, F.; Cayrel, R.; Hammer, F.; Hill, V.; Nonino, M.; Randich, S.; Stelzer, B.; Zaggia, S. Bibcode: 2011AN....332..251B Altcode: 2011arXiv1101.3139B Some insight on the first generation of stars can be obtained from the chemical composition of their direct descendants, extremely metal-poor stars (EMP), with metallicity less than or equal to 1/1000 of the solar metallicity. Such stars are exceedingly rare, the most successful surveys, for this purpose, have so far provided only about 100 stars with 1/1 000 the solar metallicity and 4 stars with about 1/10 000 of the solar metallicity. The Sloan Digital Sky Survey has the potential to provide a large number of candidates of extremely low metallicity. X-shooter has the unique capability of performing the necessary follow-up spectroscopy providing accurate metallicities and abundance ratios for several elements (Mg, Al, Ca, Ti, Cr, Sr, ...) for EMP candidates. We here report on the results for the first two stars observed in the course of our Franco-Italian X-shooter GTO. The two stars were targeted to be of metallicity around -3.0, the analysis of the X-shooter spectra showed them to be of metallicity around -2.0, but with a low α to iron ratio, which explains the underestimate of the metallicity from the SDSS spectra. The efficiency of X-shooter allows an in situ study of the outer halo, for the two stars studied here we estimate distances of 3.9 and 9.1 kpc, these are likely the most distant dwarf stars studied in detail to date.

Based on spectra obtained with X-shooter at the 8.2-m Kueyen ESO telescope, GTO programmes 085.D-0194 and 086.D.0094. Title: First stars. XIII. Two extremely metal-poor RR Lyrae stars Authors: Hansen, C. J.; Nordström, B.; Bonifacio, P.; Spite, M.; Andersen, J.; Beers, T. C.; Cayrel, R.; Spite, F.; Molaro, P.; Barbuy, B.; Depagne, E.; François, P.; Hill, V.; Plez, B.; Sivarani, T. Bibcode: 2011A&A...527A..65H Altcode: 2011arXiv1101.2207H Context. The chemical composition of extremely metal-poor stars (EMP stars; [Fe/H] < ~ -3) is a unique tracer of early nucleosynthesis in the Galaxy. As such stars are rare, we wish to find classes of luminous stars which can be studied at high spectral resolution.
Aims: We aim to determine the detailed chemical composition of the two EMP stars CS 30317-056 and CS 22881-039, originally thought to be red horizontal-branch (RHB) stars, and compare it to earlier results for EMP stars as well as to nucleosynthesis yields from various supernova (SN) models. In the analysis, we discovered that our targets are in fact the two most metal-poor RR Lyrae stars known.
Methods: Our detailed abundance analysis, taking into account the variability of the stars, is based on VLT/UVES spectra (R ≃ 43 000) and 1D LTE OSMARCS model atmospheres and synthetic spectra. For comparison with SN models we also estimate NLTE corrections for a number of elements.
Results: We derive LTE abundances for the 16 elements O, Na, Mg, Al, Si, S, Ca, Sc, Ti, Cr, Mn, Fe, Co, Ni, Sr and Ba, in good agreement with earlier values for EMP dwarf, giant and RHB stars. Li and C are not detected in either star. NLTE abundance corrections are newly calculated for O and Mg and taken from the literature for other elements. The resulting abundance pattern is best matched by model yields for supernova explosions with high energy and/or significant asphericity effects.
Conclusions: Our results indicate that, except for Li and C, the surface composition of EMP RR Lyr stars is not significantly affected by mass loss, mixing or diffusion processes; hence, EMP RR Lyr stars should also be useful tracers of the chemical evolution of the early Galactic halo. The observed abundance ratios indicate that these stars were born from an ISM polluted by energetic, massive (25-40 M⊙) and /or aspherical supernovae, but the NLTE corrections for Sc and certain other elements do play a role in the choice of model.

Based on observations made with the ESO Very Large Telescope at Paranal Observatory, Chile (Large Programme "First Stars", ID 165.N-0276(A); P.I. R. Cayrel).Table 5 and Appendix A are only available in electronic form at http://www.aanda.org Title: Probing the Galactic thick disc vertical properties and interfaces Authors: Katz, D.; Soubiran, C.; Cayrel, R.; Barbuy, B.; Friel, E.; Bienaymé, O.; Perrin, M. -N. Bibcode: 2011A&A...525A..90K Altcode:
Aims: This work investigates the properties (metallicity and kinematics) and interfaces of the Galactic thick disc as a function of height above the Galactic plane. The main aim is to study the thick disc in a place where it is the main component of the sample.
Methods: We take advantage of former astrometric work in two fields of several square degrees in which accurate proper motions were measured down to V-magnitudes of 18.5 in two directions, one near the north galactic pole and the other at a galactic latitude of 46° and galactic longitude near 0°. Spectroscopic observations have been acquired in these two fields for a total of about 400 stars down to magnitude 18.0, at spectral resolutions of 3.5 to 6.25 Å. The spectra have been analysed with the code ETOILE, comparing the target stellar spectra with a grid of 1400 reference stellar spectra. This comparison allowed us to derive the parameters effective temperature, gravity, [Fe/H] and absolute magnitude for each target star.
Results: The Metallicity Distribution Function (MDF) of the thin-thick-disc-halo system is derived for several height intervals between 0 and 5 kpc above the Galactic plane. The MDFs show a decrease of the ratio of the thin to thick disc stars between the first and second kilo-parsec. This is consistent with the classical modelling of the vertical density profile of the disc with 2 populations with different scale heights. A vertical metallicity gradient, ∂[Fe/H]/∂z = -0.068 ± 0.009 dex kpc-1, is observed in the thick disc. It is discussed in terms of scenarios of formation of the thick disc.

Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii and at the T193cm telescope, Observatoire de Haute-Provence, France.Full Tables A.1-A.3, B.1-B.3 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/525/A90 Title: The metal-poor end of the Spite plateau. I. Stellar parameters, metallicities, and lithium abundances Authors: Sbordone, L.; Bonifacio, P.; Caffau, E.; Ludwig, H. -G.; Behara, N. T.; González Hernández, J. I.; Steffen, M.; Cayrel, R.; Freytag, B.; van't Veer, C.; Molaro, P.; Plez, B.; Sivarani, T.; Spite, M.; Spite, F.; Beers, T. C.; Christlieb, N.; François, P.; Hill, V. Bibcode: 2010A&A...522A..26S Altcode: 2010arXiv1003.4510S Context. The primordial nature of the Spite plateau is at odds with the WMAP satellite measurements, implying a primordial Li production at least three times higher than observed. It has also been suggested that A(Li) might exhibit a positive correlation with metallicity below [Fe/H] ~ -2.5. Previous samples studied comprised few stars below [Fe/H] = -3.
Aims: We present VLT-UVES Li abundances of 28 halo dwarf stars between [Fe/H] = -2.5 and -3.5, ten of which have [Fe/H] <-3.
Methods: We determined stellar parameters and abundances using four different Teff scales. The direct infrared flux method was applied to infrared photometry. Hα wings were fitted with two synthetic grids computed by means of 1D LTE atmosphere models, assuming two different self-broadening theories. A grid of Hα profiles was finally computed by means of 3D hydrodynamical atmosphere models. The Li i doublet at 670.8 nm has been used to measure A(Li) by means of 3D hydrodynamical NLTE spectral syntheses. An analytical fit of A(Li)3D, NLTE as a function of equivalent width, Teff, log g, and [Fe/H] has been derived and is made available.
Results: We confirm previous claims that A(Li) does not exhibit a plateau below [Fe/H] = -3. We detect a strong positive correlation with [Fe/H] that is insensitive to the choice of Teff estimator. From a linear fit, we infer a steep slope of about 0.30 dex in A(Li) per dex in [Fe/H], which has a significance of 2-3σ. The slopes derived using the four Teff estimators are consistent to within 1σ. A significant slope is also detected in the A(Li)-Teff plane, driven mainly by the coolest stars in the sample (Teff < 6250), which appear to be Li-poor. However, when we remove these stars the slope detected in the A(Li)-[Fe/H] plane is not altered significantly. When the full sample is considered, the scatter in A(Li) increases by a factor of 2 towards lower metallicities, while the plateau appears very thin above [Fe/H] = -2.8. At this metallicity, the plateau lies at <A(Li)3D, NLTE> = 2.199±0.086.
Conclusions: The meltdown of the Spite plateau below [Fe/H] ~ -3 is established, but its cause is unclear. If the primordial A(Li) were that derived from standard 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. That no star below [Fe/H] = -3 lies above the plateau suggests that they formed at plateau level and experienced subsequent depletion.

Based on observations made with the ESO Very Large Telescope at Paranal Observatory, Chile (Programmes 076.A-0463 and 077.D-0299).Full Table 3 is available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/522/A26IDL code (appendix) is only available in electronic form at http://www.aanda.org Title: VizieR Online Data Catalog: Thick disc vertical properties (Katz+, 2011) Authors: Katz, D.; Soubiran, C.; Cayrel, R.; Barbuy, B.; Friel, E.; Bienayme, O.; Perrin, M. -N. Bibcode: 2010yCat..35250090K Altcode: 2010yCat..35259090K Tables A1, A2 and A3: coordinates and parameters of the 346 CARELEC and CFHT program stars analysed in this study.

Table B1: parameters of the 1398 ELODIE reference spectra used to derive the stellar characteristics of the program stars.

Tables B2 and B3: parameters of the 45 CARELEC validation stars and 46 CFHT validation stars used to assess the accuracy and precision of the stellar atmospheric parameters derivation method. It should be noted that 2 stars "of" M71 (KC-124, KC-223) and 3 stars "of" M5 (I-52, III-44 and IV-61) discussed in the article but considered as not belonging to these clusters are not listed in table B3.

(6 data files). Title: VizieR Online Data Catalog: Fe Abundances in metal-poor stars (Sbordone+ 2010) Authors: Sbordone, L.; Bonifacio, P.; Caffau, E.; Ludwig, H. -G.; Behara, N. T.; Gonzalez Hernandez, J. I.; Steffen, M.; Cayrel, R.; Freytag, B.; van't Veer, C.; Molaro, P.; Plez, B.; Sivarani, T.; Spite, M.; Spite, F.; Beers, T. C.; Christlieb, N.; Francois, P.; Hill, V. Bibcode: 2010yCat..35220026S Altcode: 2010yCat..35229026S Line-by-line abundances for FeI and FeII lines used to estimate metallicity and gravity for the program stars. The first column lists the star name, then the ion (FeI or FeII) The the wavelength in nm, the loggf, the measured EW (pm) and the derived abundance assuming the four stellar parameter sets used in the article, respectively 3D, BA, ALI and IRFM.

(3 data files). Title: Convection and 6Li in the atmospheres of metal-poor halo stars Authors: Steffen, Matthias; Cayrel, R.; Bonifacio, P.; Ludwig, H. -G.; Caffau, E. Bibcode: 2010IAUS..268..215S Altcode: 2010arXiv1001.3274S Based on 3D hydrodynamical model atmospheres computed with the CO5BOLD code and 3D non-LTE (NLTE) line formation calculations, we study the effect of the convection-induced line asymmetry on the derived 6Li abundance for a range in effective temperature, gravity, and metallicity covering the stars of the Asplund et al. (2006) sample. When the asymmetry effect is taken into account for this sample of stars, the resulting 6Li/7Li ratios are reduced by about 1.5% on average with respect to the isotopic ratios determined by Asplund et al. (2006). This purely theoretical correction diminishes the number of significant 6Li detections from 9 to 4 (2σ criterion), or from 5 to 2 (3σ criterion). In view of this result the existence of a 6Li plateau appears questionable. A careful reanalysis of individual objects by fitting the observed lithium 6707 Å doublet both with 3D NLTE and 1D LTE synthetic line profiles confirms that the inferred 6Li abundance is systematically lower when using 3D NLTE instead of 1D LTE line fitting. Nevertheless, halo stars with unquestionable 6Li detection do exist even if analyzed in 3D-NLTE, the most prominent example being HD 84937. Title: The metal-poor end of the Spite plateau: gravity sensitivity of the Hα wings fitting. Authors: Sbordone, L.; Bonifacio, P.; Caffau, E.; Ludwig, H. -G.; Behara, N.; Gonzalez-Hernandez, J. I.; Steffen, M.; Cayrel, R.; Freytag, B.; Van't Veer, C.; Molaro, P.; Plez, B.; Sivarani, T.; Spite, M.; Spite, F.; Beers, T. C.; Christlieb, N.; François, P.; Hill, V. Bibcode: 2010IAUS..268..355S Altcode: 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. Title: Main-sequence and sub-giant stars in the globular cluster NGC 6397: The complex evolution of the lithium abundance Authors: González Hernández, J. I.; Bonifacio, P.; Caffau, E.; Steffen, M.; Ludwig, H. -G.; Behara, N.; Sbordone, L.; Cayrel, R.; Zaggia, S. Bibcode: 2010IAUS..268..257G Altcode: 2009arXiv0912.4105G Thanks to the high multiplex and efficiency of Giraffe at the VLT we have been able for the first time to observe the Li I doublet in the Main Sequence stars of a globular cluster. At the same time we observed Li in a sample of Sub-Giant stars of the same B-V colour.

Our final sample is composed of 84 SG stars and 79 MS stars. In spite of the fact that SG and MS span the same temperature range we find that the equivalent widths of the Li I doublet in SG stars are systematically larger than those in MS stars, suggesting a higher Li content among SG stars. This is confirmed by our quantitative analysis carried out making use of 1D hydrostatic plane-parallel models and 3D hydrodynamical simulations of the stellar atmospheres.

We derived the effective temperatures of stars in our the sample from Hα fitting. Theoretical profiles were computed using 3D hydrodynamical simulations and 1D ATLAS models. Therefore, we are able to determined 1D and 3D-based effective temperatures. We then infer Li abundances taking into account non-local thermodynamical equilibrium effects when using both 1D and 3D models.

We find that SG stars have a mean Li abundance higher by 0.1 dex than MS stars. This result is obtained using both 1D and 3D models. We also detect a positive slope of Li abundance with effective temperature, the higher the temperature the higher the Li abundance, both for SG and MS stars, although the slope is slightly steeper for MS stars. These results provide an unambiguous evidence that the Li abundance changes with evolutionary status.

The physical mechanisms responsible for this behaviour are not yet clear, and none of the existing models seems to describe accurately these observations. Based on these conclusions, we believe that the cosmological lithium problem still remains an open question. Title: 6Li in metal-poor halo stars: real or spurious? Authors: Steffen, M.; Cayrel, R.; Bonifacio, P.; Ludwig, H. -G.; Caffau, E. Bibcode: 2010IAUS..265...23S Altcode: 2009arXiv0910.5917S The presence of convective motions in the atmospheres of metal-poor halo stars leads to systematic asymmetries of the emergent spectral line profiles. Since such line asymmetries are very small, they can be safely ignored for standard spectroscopic abundance analysis. However, when it comes to the determination of the 6Li/7Li isotopic ratio, q(Li)=n(6Li)/n(7Li), the intrinsic asymmetry of the 7Li line must be taken into account, because its signature is essentially indistinguishable from the presence of a weak 6Li blend in the red wing of the 7Li line. In this contribution we quantity the error of the inferred 6Li/7Li isotopic ratio that arises if the convective line asymmetry is ignored in the fitting of the λ6707 Å lithium blend. Our conclusion is that 6Li/7Li ratios derived by Asplund et al. (2006), using symmetric line profiles, must be reduced by typically Δq(Li) ≈ 0.015. This diminishes the number of certain 6Li detections from 9 to 4 stars or less, casting some doubt on the existence of a 6Li plateau. Title: Evolution of [O/Mg], [Na/Mg], [Al/Mg], and [K/Mg] in the Galaxy, from a NLTE analysis Authors: Spite, M.; Spite, F.; Bonifacio, P.; Hill, V.; Andrievsky, S.; Cayrel, R.; François, P.; Korotin, S. Bibcode: 2010IAUS..265..380S Altcode: 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. Title: HST-STIS abundances in the uranium-rich very metal-poor star CS 31082-001 Authors: Barbuy, B.; Spite, M.; Hill, V.; Primas, F.; Plez, B.; Cayrel, R.; Sneden, C.; Spite, F.; Beers, T. C.; Andersen, J.; Nordström, B.; Bonifacio, P.; François, P.; Molaro, P.; Siqueira-Mello, C. Bibcode: 2010IAUS..265..120B Altcode: 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. Title: Solar abundances and 3D model atmospheres Authors: Ludwig, Hans-Günter; Caffau, Elisabetta; Steffen, Matthias; Bonifacio, Piercarlo; Freytag, Bernd; Cayrel, Roger Bibcode: 2010IAUS..265..201L Altcode: 2009arXiv0911.4248L We present solar photospheric abundances for 12 elements from optical and near-infrared spectroscopy. The abundance analysis was conducted employing 3D hydrodynamical (CO5BOLD) as well as standard 1D hydrostatic model atmospheres. We compare our results to others with emphasis on discrepancies and still lingering problems, in particular exemplified by the pivotal abundance of oxygen. We argue that the thermal structure of the lower solar photosphere is very well represented by our 3D model. We obtain an excellent match of the observed center-to-limb variation of the line-blanketed continuum intensity, also at wavelengths shortward of the Balmer jump. Title: The metal-poor end of the Spite plateau Authors: Sbordone, L.; Bonifacio, P.; Caffau, E.; Ludwig, H. -G.; Behara, N.; Gonzalez-Hernandez, J. I.; Steffen, M.; Cayrel, R.; Freytag, B.; Van't Veer, C.; Molaro, P.; Plez, B.; Sivarani, T.; Spite, M.; Spite, F.; Beers, T. C.; Christlieb, N.; François, P.; Hill, V. Bibcode: 2010IAUS..265...75S Altcode: 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. Title: NLTE strontium abundances in extremely metal poor halo stars Authors: Andrievsky, S.; Spite, M.; Korotin, S.; Spite, F.; Bonifacio, P.; Cayrel, R.; Francois, P.; Hill, V. Bibcode: 2010nuco.confE..94A Altcode: 2010PoS...100E..94A No abstract at ADS Title: Non-LTE abundances of Mg and K in extremely metal-poor stars and the evolution of [O/Mg], [Na/Mg], [Al/Mg], and [K/Mg] in the Milky Way Authors: Andrievsky, S. M.; Spite, M.; Korotin, S. A.; Spite, F.; Bonifacio, P.; Cayrel, R.; François, P.; Hill, V. Bibcode: 2010A&A...509A..88A Altcode: 2010arXiv1001.1207A
Aims: LTE abundances of light elements in extremely metal-poor (EMP) stars have been previously derived from high quality spectra. New derivations, free from the NLTE effects, will better constrain the models of the Galactic chemical evolution and the yields of the very first supernovae.
Methods: The NLTE profiles of the magnesium and potassium lines have been computed in a sample of 53 extremely metal-poor stars with a modified version of the program MULTI and adjusted to the observed lines in order to derive the abundances of these elements.
Results: The NLTE corrections for magnesium and potassium are in good agreement with the works found in the literature. The abundances are slightly changed, reaching a better precision: the scatter around the mean of the abundance ratios has decreased. Magnesium may be used with confidence as reference element. Together with previously determined NLTE abundances of sodium and aluminum, the new ratios are displayed, for comparison, along the theoretical trends proposed by some models of the chemical evolution of the Galaxy, using different models of supernovae.

Based on observations obtained with the ESO Very Large Telescope at Paranal Observatory (Large Programme “First Stars”, ID 165.N-0276; P.I.: R. Cayrel. Title: Lithium abundances of main-sequence and subgiant stars in the globular cluster NGC 6397 Authors: González Hernández, J. I.; Bonifacio, P.; Caffau, E.; Steffen, M.; Ludwig, H. -G.; Behara, N.; Sbordone, L.; Cayrel, R.; Zaggia, S. Bibcode: 2010IAUS..266..407G Altcode: 2009arXiv0910.2305G We present FLAMES/GIRAFFE spectroscopy obtained with the Very Large Telescope (VLT). Using these observations, we have been able (for the first time) to observe the Lii doublet in the main-sequence (MS) stars of a globular cluster. We also observed Li in a sample of subgiant (SG) stars of the same B - V colour. Our final sample is composed of 84 SG and 79 MS stars. In spite of the fact that SG and MS stars span the same temperature range, we find that the equivalent widths of the Lii doublet in SG stars are systematically greater than in MS stars, suggesting a higher Li content among SG stars. This is confirmed by our quantitative analysis, which makes use of both 1D and 3D model atmospheres. We find that SG stars show, on average, a higher Li abundance, by 0.1 dex, than MS stars. We also detect a positive slope of Li abundance with effective temperature: the higher the temperature the higher the Li abundance, both for SG and MS stars, although the slope is slightly steeper for MS stars. These results provide unambiguous evidence that the Li abundance changes with evolutionary state. The physical mechanisms that contribute to this are not yet clear, since none of the proposed models seem to describe accurately the observations. Whether such a mechanism can explain the cosmological lithium problem is still an open question. Title: HST-STIS abundances in the uranium-rich metal-poor star CS31082-001 Authors: Barbuy, B.; Spite, M.; Hill, V.; Primas, F.; Plez, B.; Cayrel, R.; Sneden, C.; Beers, T.; Andersen, J. R.; Nordström, B.; Bonifacio, P.; Francois, P.; Molaro, P. Bibcode: 2010nuco.confE..77B Altcode: 2010PoS...100E..77B No abstract at ADS Title: Lithium in the globular cluster NGC 6397. Evidence for dependence on evolutionary status Authors: González Hernández, J. I.; Bonifacio, P.; Caffau, E.; Steffen, M.; Ludwig, H. -G.; Behara, N. T.; Sbordone, L.; Cayrel, R.; Zaggia, S. Bibcode: 2009A&A...505L..13G Altcode: 2009arXiv0909.0983G Context: Most globular clusters are believed to host a single stellar population. They can thus be considered a good place to study the Spite plateau and to search for possible evolutionary modifications of the Li content.
Aims: We want to determine the Li content of subgiant (SG) and main sequence (MS) stars of the old, metal-poor globular cluster NGC 6397. This work was aimed not only at studying possible Li abundance variations but also to investigate the cosmological Li discrepancy.
Methods: Here, we present FLAMES/GIRAFFE observations of a sample of 84 SG and 79 MS stars in NGC 6397 selected in a narrow range of B-V colour and, therefore, effective temperatures. We determine both effective temperatures and Li abundances using three-dimensional hydrodynamical model atmospheres for all the MS and SG stars of the sample.
Results: We find a significant difference in the Li abundance between SG stars and MS stars, the SG stars having an abundance higher by almost 0.1 dex on average. We also find a decrease in the lithium abundance with decreasing effective temperature, both in MS and SG stars, albeit with a significantly different slope for the two classes of stars. This suggests that the lithium abundance in these stars is, indeed, altered by some process, which is temperature-dependent.
Conclusions: The lithium abundance pattern observed in NGC 6397 is different from what is found among field stars, casting some doubt on the use of globular cluster stars as representative of Population II with respect to the lithium abundance. None of the available theories of Li depletion appears to satisfactorily describe our observations.

Based on observations obtained with FLAMES/GIRAFFE at VLT Kueyen 8.2 m telescope in programme 079.D-0399(A). Table and Figs. 3-10 are only available in electronic form at http://www.aanda.org Table 2 is available in electronic form at http://www.aanda.org and at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/505/L13 Title: VizieR Online Data Catalog: Lithium in NGC 6397 (Gonzalez Hernandez+, 2009) Authors: Gonzalez Hernandez, J. I.; Bonifacio, P.; Caffau, E.; Steffen, M.; Ludwig, H. -G.; Behara, N. T.; Sbordone, L.; Cayrel, R.; Zaggia, S. Bibcode: 2009yCat..35059013G Altcode: Photometric data of the dwarf and subgiant stars of the globular cluster NGC 6397. We also provide the signal-to-noise of the spectra, the 3D and 1D Halpha-based effective temperatures, 3D Li abundances, and the equivalent widths and errors: dEWa: Error of the equivalent width measurements estimated from a fitting routine that uses as free parameters the velocity shift, the continuum location, and the equivalent width of the Li line. dEWb: Error of the equivalent width associated to the signal-to-noise ratio and the wavelength dispersion of the spectra, derived using Cayrel's formula (Cayrel, 1988, IAU Symp. 132: The Impact of Very High S/N Spectroscopy on Stellar Physics, 132, 345).

(1 data file). Title: VizieR Online Data Catalog: Extremely metal-poor turnoff stars abundances (Bonifacio+, 2009) Authors: Bonifacio, P.; Spite, M.; Cayrel, R.; Hill, V.; Spite, F.; Francois, P.; Plez, B.; Ludwig, H. -G.; Caffau, E.; Molaro, P.; Depagne, E.; Andersen, J.; Barbuy, B.; Beers, T. C.; Nordstroem, B.; Primas, F. Bibcode: 2009yCat..35010519B Altcode: The detailed chemical abundances of extremely metal-poor (EMP) stars are key guides to understanding the early chemical evolution of the Galaxy. Most existing data, however, treat giant stars that may have experienced internal mixing later. We aim to compare the results for giants with new, accurate abundances for all observable elements in 18 EMP turnoff stars. VLT/UVES spectra at ~45000 and S/N ~130 per pixel (330-1000nm) are analysed with OSMARCS model atmospheres and the TURBOSPECTRUM code to derive abundances for C, Mg, Si, Ca, Sc, Ti, Cr, Mn, Co, Ni, Zn, Sr, and Ba. For Ca, Ni, Sr, and Ba, we find excellent consistency with our earlier sample of EMP giants, at all metallicities. However, our abundances of C, Sc, Ti, Cr, Mn and Co are ~0.2dex larger than in giants of similar metallicity. Mg and Si abundances are ~0.2dex lower (the giant [Mg/Fe] values are slightly revised), while Zn is again ~0.4dex higher than in giants of similar [Fe/H] (6 stars only). For C, the dwarf/giant discrepancy could possibly have an astrophysical cause, but for the other elements it must arise from shortcomings in the analysis. Approximate computations of granulation (3D) effects yield smaller corrections for giants than for dwarfs, but suggest that this is an unlikely explanation, except perhaps for C, Cr, and Mn. NLTE computations for Na and Al provide consistent abundances between dwarfs and giants, unlike the LTE results, and would be highly desirable for the other discrepant elements as well. Meanwhile, we recommend using the giant abundances as reference data for Galactic chemical evolution models.

(3 data files). Title: First stars XII. Abundances in extremely metal-poor turnoff stars, and comparison with the giants Authors: Bonifacio, P.; Spite, M.; Cayrel, R.; Hill, V.; Spite, F.; François, P.; Plez, B.; Ludwig, H. -G.; Caffau, E.; Molaro, P.; Depagne, E.; Andersen, J.; Barbuy, B.; Beers, T. C.; Nordström, B.; Primas, F. Bibcode: 2009A&A...501..519B Altcode: 2009arXiv0903.4174B Context: The detailed chemical abundances of extremely metal-poor (EMP) stars are key guides to understanding the early chemical evolution of the Galaxy. Most existing data, however, treat giant stars that may have experienced internal mixing later.
Aims: We aim to compare the results for giants with new, accurate abundances for all observable elements in 18 EMP turnoff stars.
Methods: VLT/UVES spectra at R ~ 45 000 and S/N ~ 130 per pixel (λλ 330-1000 nm) are analysed with OSMARCS model atmospheres and the TURBOSPECTRUM code to derive abundances for C, Mg, Si, Ca, Sc, Ti, Cr, Mn, Co, Ni, Zn, Sr, and Ba.
Results: For Ca, Ni, Sr, and Ba, we find excellent consistency with our earlier sample of EMP giants, at all metallicities. However, our abundances of C, Sc, Ti, Cr, Mn and Co are ~0.2 dex larger than in giants of similar metallicity. Mg and Si abundances are ~0.2 dex lower (the giant [Mg/Fe] values are slightly revised), while Zn is again ~0.4 dex higher than in giants of similar [Fe/H] (6 stars only).
Conclusions: For C, the dwarf/giant discrepancy could possibly have an astrophysical cause, but for the other elements it must arise from shortcomings in the analysis. Approximate computations of granulation (3D) effects yield smaller corrections for giants than for dwarfs, but suggest that this is an unlikely explanation, except perhaps for C, Cr, and Mn. NLTE computations for Na and Al provide consistent abundances between dwarfs and giants, unlike the LTE results, and would be highly desirable for the other discrepant elements as well. Meanwhile, we recommend using the giant abundances as reference data for Galactic chemical evolution models.

Based on observations obtained with the ESO Very Large Telescope at Paranal Observatory, Chile (Large Programme “First Stars”, ID 165.N-0276; P.I.: R. Cayrel, and Programme 078.B-0238; P.I.: M. Spite). Appendices A-C are only available in electronic form at http://www.aanda.org Table 7 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/501/519 Title: Chemical composition and kinematics of Galactic disk stars. Commentary on: Edvardsson B., Andersen J., Gustafsson B., et al., 1993, A&A, 275, 101 Authors: Barbuy, B.; Cayrel, R. Bibcode: 2009A&A...500..443B Altcode: No abstract at ADS Title: Tracing SN yields in metal-poor HB stars Authors: Hansen, C. J.; Nordström, B.; Cayrel, R.; Spite, M.; Spite, F.; Hill, V.; Plez, B.; Andersen, J.; Beers, T. C.; Sivarani, T.; Depagne, E.; François, P.; Primas, F.; Barbuy, B. Bibcode: 2009IAUS..254P..31H Altcode: No abstract at ADS Title: Halo chemistry and first stars. The chemical composition of the matter in the early Galaxy, from C to Mg† Authors: Spite, M.; Bonifacio, P.; Cayrel, R.; Spite, F.; Francois, P.; Ludwig, H. G.; Caffau, E.; Andrievsky, S.; Barbuy, B.; Plez, B.; Molaro, P.; Andersen, J.; Beers, T.; Depagne, E.; Nordström, B.; Primas, F. Bibcode: 2009IAUS..254..349S Altcode: 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. Title: Evolution of the barium abundance in the early Galaxy from a NLTE analysis of the Ba lines in a homogeneous sample of EMP stars Authors: Andrievsky, S. M.; Spite, M.; Korotin, S. A.; Spite, F.; François, P.; Bonifacio, P.; Cayrel, R.; Hill, V. Bibcode: 2009A&A...494.1083A Altcode: 2009arXiv0902.0450A Context: Barium is a key element in constraining the evolution of the (not well understood) r-process in the first galactic stars and currently the Ba abundances in these very metal-poor stars were mostly measured under the Local Thermodynamical Equilibrium (LTE) assumption, which may lead in general to an underestimation of Ba.
Aims: We present here determinations of the barium abundance taking into account the non-LTE (NLTE) effects in a sample of extremely metal-poor stars (EMP stars): 6 turnoff stars and 35 giants.
Methods: The NLTE profiles of the three unblended Ba II lines (4554 Å, 5853 Å, 6496 Å) have been computed. The computations were made with a modified version of the MULTI code, applied to an atomic model of the Ba atom with 31 levels of Ba I, 101 levels of Ba II, and compared to the observations.
Results: The ratios of the NLTE abundances of barium relative to Fe are slightly shifted towards the solar ratio. In the plot of [Ba/Fe] versus [Fe/H], the slope of the regression line is slightly reduced as is the scatter. In the interval -3.3 <[Fe/H] < -2.6, [Ba/Fe] decreases with a slope of about 1.4 and a scatter close to 0.44. For [Fe/H] <-3.3 the number of stars is not sufficient to decide whether [Ba/Fe] keeps decreasing (and then CD-38:245 should be considered as a peculiar “barium-rich star”) or if a plateau is reached as soon as [Ba/Fe] ≈ -1. In both cases the scatter remains quite large, larger than what can be accounted for by the measurement and determination errors, suggesting the influence of a complex process of Ba production, and/or inefficient mixing in the early Galaxy.

Based on observations obtained with the ESO Very Large Telescope at Paranal Observatory (Large Programme “First Stars”, ID 165.N-0276; P.I.: R. Cayrel. Title: The ESO Large Programme ``First Stars'' Authors: Bonifacio, P.; Andersen, J.; Andrievsky, S. M.; Barbuy, B.; Beers, T. C.; Caffau, E.; Cayrel, R.; Depagne, E.; François, P.; González Hernández, J. I.; Hansen, C. J.; Herwig, F.; Hill, V.; Korotin, S. A.; Ludwig, H. -G.; Molaro, P.; Nordström, B.; Plez, B.; Primas, F.; Sivarani, T.; Spite, F.; Spite, M. Bibcode: 2009ASSP....9...31B Altcode: 2008arXiv0801.1293B; 2009svlt.conf...31B In ESO period 65 (April-September 2000) the large programme 165.N-0276, led by Roger Cayrel, began making use of UVES at the Kueyen VLT telescope. Known within the Team and outside as "First Stars", it was aimed at obtaining high resolution, high signal-to-noise ratio spectra in the range 320 nm-1000 nm for a large sample of extremely metal-poor (EMP) stars identified from the HK objective prism survey [T.C. Beers, G.W. Preston, S.A. Shectman in Astron. J. 90, 2089 (1985); T.C. Beers, G.W. Preston, S.A. Shectman in Astron. J. 103, 1987 (1992)]. The goal was to use these spectra to determine accurate atmospheric parameters and chemical composition of these stars which are among the oldest objects amenable to our detailed study. Although these stars are not the first generation of stars they must be very close descendants of the first generation. One may hope to gain insight on the nature of the progenitors from detailed information on the descendants. Title: The photospheric solar oxygen project. I. Abundance analysis of atomic lines and influence of atmospheric models Authors: Caffau, E.; Ludwig, H. -G.; Steffen, M.; Ayres, T. R.; Bonifacio, P.; Cayrel, R.; Freytag, B.; Plez, B. Bibcode: 2008A&A...488.1031C Altcode: 2008arXiv0805.4398C Context: The solar oxygen abundance has undergone a major downward revision in the past decade, the most noticeable one being the update including 3D hydrodynamical simulations to model the solar photosphere. Up to now, such an analysis has only been carried out by one group using one radiation-hydrodynamics code.
Aims: We investigate the photospheric oxygen abundance considering lines from atomic transitions. We also consider the relationship between the solar model used and the resulting solar oxygen abundance, to understand whether the downward abundance revision is specifically related to 3D hydrodynamical effects.
Methods: We performed a new determination of the solar photospheric oxygen abundance by analysing different high-resolution high signal-to-noise ratio atlases of the solar flux and disc-centre intensity, making use of the latest generation of CO5BOLD 3D solar model atmospheres.
Results: We find 8.73 ≤ log (N_O/N_H) +12 ≤ 8.79. The lower and upper values represent extreme assumptions on the role of collisional excitation and ionisation by neutral hydrogen for the NLTE level populations of neutral oxygen. The error of our analysis is ± (0.04± 0.03) dex, the last being related to NLTE corrections, the first error to any other effect. The 3D “granulation effects” do not play a decisive role in lowering the oxygen abundance.
Conclusions: Our recommended value is log (N_O/N_H) = 8.76 ± 0.07, considering our present ignorance of the role of collisions with hydrogen atoms on the NLTE level populations of oxygen. The reasons for lower O abundances in the past are identified as (1) the lower equivalent widths adopted and (2) the choice of neglecting collisions with hydrogen atoms in the statistical equilibrium calculations for oxygen.

This paper is dedicated to the memory of Hartmut Holweger. Title: NLTE determination of the aluminium abundance in a homogeneous sample of extremely metal-poor stars Authors: Andrievsky, S. M.; Spite, M.; Korotin, S. A.; Spite, F.; Bonifacio, P.; Cayrel, R.; Hill, V.; François, P. Bibcode: 2008A&A...481..481A Altcode: 2008arXiv0802.1519A Aims: Aluminium is a key element to constrain the models of the chemical enrichment and the yields of the first supernovae. But obtaining precise Al abundances in extremely metal-poor (EMP) stars requires that the non-LTE effects be carefully taken into account.
Methods: The NLTE profiles of the blue resonance aluminium lines have been computed in a sample of 53 extremely metal-poor stars with a modified version of the program MULTI applied to an atomic model of the Al atom with 78 levels of Al I and 13 levels of Al II, and compared to the observations.
Results: With these new determinations, all the stars of the sample show a ratio Al/Fe close to the solar value: [Al/Fe] = -0.06±0.10 with a very small scatter. These results are compared to the models of the chemical evolution of the halo using different models of SN II and are compatible with recent computations. The sodium-rich giants are not found to be also aluminium-rich and thus, as expected, the convection in these giants only brings to the surface the products of the Ne-Na cycle.

Based on observations obtained with the ESO Very Large Telescope at Paranal Observatory, Chile (Large Programme “First Stars”, ID 165.N-0276(A); P.I.: R. Cayrel). Title: First stars XI. Chemical composition of the extremely metal-poor dwarfs in the binary CS 22876-032 Authors: González Hernández, J. I.; Bonifacio, P.; Ludwig, H. -G.; Caffau, E.; Spite, M.; Spite, F.; Cayrel, R.; Molaro, P.; Hill, V.; François, P.; Plez, B.; Beers, T. C.; Sivarani, T.; Andersen, J.; Barbuy, B.; Depagne, E.; Nordström, B.; Primas, F. Bibcode: 2008A&A...480..233G Altcode: 2007arXiv0712.2949G Context: Unevolved metal-poor stars constitute a fossil record of the early Galaxy, and can provide invaluable information on the properties of the first generations of stars. Binary systems also provide direct information on the stellar masses of their member stars.
Aims: The purpose of this investigation is a detailed abundance study of the double-lined spectroscopic binary CS 22876-032, which comprises the two most metal-poor dwarfs known.
Methods: We used high-resolution, high-S/N ratio spectra from the UVES spectrograph at the ESO VLT telescope. Long-term radial-velocity measurements and broad-band photometry allowed us to determine improved orbital elements and stellar parameters for both components. We used OSMARCS 1D models and the turbospectrum spectral synthesis code to determine the abundances of Li, O, Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Mn, Fe, Co and Ni. We also used the CO^5BOLD model atmosphere code to compute the 3D abundance corrections, notably for Li and O.
Results: We find a metallicity of [Fe/H] ~ -3.6 for both stars, using 1D models with 3D corrections of ~-0.1 dex from averaged 3D models. We determine the oxygen abundance from the near-UV OH bands; the 3D corrections are large, -1 and -1.5 dex for the secondary and primary respectively, and yield [O/Fe] ~ 0.8, close to the high-quality results obtained from the [OI] 630 nm line in metal-poor giants. Other [ α/Fe] ratios are consistent with those measured in other dwarfs and giants with similar [Fe/H], although Ca and Si are somewhat low ([X/Fe] ⪉ 0). Other element ratios follow those of other halo stars. The Li abundance of the primary star is consistent with the Spite plateau, but the secondary shows a lower abundance; 3D corrections are small.
Conclusions: The Li abundance in the primary star supports the extension of the Spite Plateau value at the lowest metallicities, without any decrease. The low abundance in the secondary star could be explained by endogenic Li depletion, due to its cooler temperature. If this is not the case, another, yet unknown mechanism may be causing increased scatter in A(Li) at the lowest metallicities. Title: Self-broadening of the hydrogen Balmer α line Authors: Allard, N. F.; Kielkopf, J. F.; Cayrel, R.; van't Veer-Menneret, C. Bibcode: 2008A&A...480..581A Altcode: Context: Profiles of hydrogen lines in stellar spectra are determined by the properties of the hydrogen atom and the structure of the star's atmosphere. Hydrogen line profiles are therefore a very important diagnostic tool in stellar modeling. In particular they are widely used as effective temperature criterion for stellar atmospheres in the range T_eff 5500-7000 K.
Aims: In cool stars such as the Sun hydrogen is largely neutral and the electron density is low. The line center width at half maximum and the spectral energy distribution in the wings are determined primarily by collisions with hydrogen atoms due to their high relative density. This work aims to provide benchmark calculations of Balmer α based on recent H2 potentials.
Methods: For the first time an accurate determination of the broadening of Balmer α by atomic hydrogen is made in a unified theory of collisional line profiles using ab initio calculations of molecular hydrogen potential energies and transition matrix elements among singlet and triplet electronic states.
Results: We computed the shape, width and shift of the Balmer α line perturbed by neutral hydrogen and studied their dependence on temperature. We present results over the full range of temperatures from 3000 to 12 000 K needed for stellar spectra models.
Conclusions: Our calculations lead to larger values than those obtained with the commonly used Ali & Griem (1966, Phys. Rev. A, 144, 366) theory and are closer to the recent calculations of Barklem et al. (2000a, A&A, 355, L5; 2000b, A&A, 363, 1091). We conclude that the line parameters are dependent on the sum of many contributing molecular transitions, each with a different temperature dependence, and we provide tables for Balmer α. The unified line shape theory with complete molecular potentials also predicts additional opacity in the far non-Lorentzian wing. Title: CS 22876-032: The Most Metal-Poor Dwarfs. Abundances and 3D Effects Authors: González Hernández, J. I.; Bonifacio, P.; Ludwig, H. -G.; Caffau, E.; Spite, M.; Spite, F.; Cayrel, R.; Molaro, P.; Hill, V.; François, P.; Plez, B.; Beers, T. C.; Sivarani, T.; Andersen, J.; Barbuy, B.; Depagne, E.; Nordström, B.; Primas, F. Bibcode: 2008AIPC..990..175G Altcode: 2008AIPC..990..175H Unevolved extremely metal-poor stars offer us a unique tool to infer knowledge of the first generation of stars. We have analysed UVES high-resolution spectra of the double-lined spectroscopic binary CS 22876-032 which comprises the two most metal-poor dwarfs currently known. In particular, we determine the oxygen (from OH lines in the near-UV) and lithium abundances taking into account 3D effects.

The long-time baseline radial velocity measurements and photometric data available allowed us to determine the orbital elements as well as stellar parameters of both components. We use OSMARCS 1D models and the TURBOSPECTRUM spectral synthesis code to determine the abundances of Li, O, Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Mn, Fe, Co and Ni. We also use the CO5 BOLD 3D model atmosphere code to predict the 3D abundance corrections, mainly for Li, O and Fe.

We find a metallicity of [Fe/H]~-3.6 for both stars using 1D models with 3D corrections of ~-0.1 dex from horizontal and temporal averaged 3D models. The [α/Fe] ratios are consistent with those found for metal-poor giants with similar [Fe/H], although Ca and Si are rather low, [X/Fe]~=0. The 1D O abundance, [O/Fe]~2 for both stars, is very large, but 3D models predict abundance corrections of roughly -1.0 dex and -1.5 dex for the secondary and primary stars, respectively. These 3D corrections bring the O abundances derived from near-UV OH bands in these two dwarfs closer to other high-quality measurements from the forbidden [OI] 630 nm line in metal-poor giants. The Li abundance is consistent with the Spite plateau, although the secondary star shows a lower abundance. Title: The Metal-Poor End of the Lithium Plateau Authors: Sbordone, L.; Bonifacio, P.; González Hernández, J. I.; Cayrel, R.; Behara, N.; Molaro, P.; Plez, B.; Francois, P.; Christlieb, N.; Ludwig, H. -G.; Sivarani, T.; Beers, T. C.; van't Veer, C. Bibcode: 2008AIPC..990..339S Altcode: We present our current sample of Lithium abundances in 28 low metallicity dwarf and Turn Off (TO) stars ([Fe/H] between -2.5 and -3.5), based on high resolution, high signal to noise echelle spectra. Nine new stars have been added to the Bonifacio et al. [1] sample, and the full sample has been reanalyzed in order to take into account the effect of two different possible temperature scales. In fact, the Li abundance measurement based on the 670.8 nm line is highly sensitive to temperature, and Teff scales are still poorly calibrated at low metallicities. First, the effective temperature has been derived from Hα profile fitting, and second, directly from the star's infrared flux. The two methods offer similar precision but are affected by different uncertainties and systematics. The infrared flux method (IRFM) leads to a larger Teff dispersion than the Hα profile fitting, while also producing an offset of about 150 K towards hotter temperatures. This leads to a contraction of the metallicity scale of the sample, which encompasses [Fe/H] = -3.7 to -2.5 when using Hα calibrated temperatures, and [Fe/H] = -3.4 to -2.5 when using IRFM. The higher average IRFM temperature increases somewhat the mean Li abundance, changing from A(Li)Hα = 2.10 to A(Li)IRFM = 2.18 Title: Overview of the Li problem in metal-poor stars and new results on 6Li Authors: Cayrel, R.; Steffen, M.; Bonifacio, P.; Ludwig, H. -G.; Caffau, E. Bibcode: 2008nuco.confE...2C Altcode: 2008arXiv0810.4290C; 2008PoS....53E...2C Two problems are discussed here. The first one is the 0.4 dex discrepancy between the 7Li abundance derived from the spectra of metal-poor halo stars on the one hand, and from Big Bang nucleosynthesis, based on the cosmological parameters constrained by the WMAP measurements, on the other hand. Lithium, indeed, can be depleted in the convection zone of unevolved stars. The understanding of the hydrodynamics of the crucial zone near the bottom of the convective envelope in dwarfs or turn-off stars of solar metallicity has recently made enormous progress with the inclusion of internal gravity waves. However, similar work for metal-poor stars is still lacking. Therefore it is not yet clear whether the depletion occurring in the metal-poor stars themselves is adequate to produce a 7Li plateau. The second problem pertains to the large amount of 6Li recently found in metal-poor halo stars. The convection-related asymmetry of the 7Li line could mimic the signal attributed so far to the weak blend of 6Li in the red wing of the 7Li line. Theoretical computations show that the signal generated by the asymmetry of 7Li is 2.0, 2.1, and 3.7 per cent for [Fe/H]= -3.0, -2.0, -1.0, respectively (Teff =6250 K and log g=4.0 [cgs]). In addition we re-investigate the statistical properties of the 6Li plateau and show that previous analyses were biased. Our conclusion is that the 6Li plateau can be reinterpreted in terms of intrinsic line asymmetry, without the need to invoke a contribution of 6Li. (abridged) Title: First stars. VIII. Enrichment of the neutron-capture elements in the early Galaxy Authors: François, P.; Depagne, E.; Hill, V.; Spite, M.; Spite, F.; Plez, B.; Beers, T. C.; Andersen, J.; James, G.; Barbuy, B.; Cayrel, R.; Bonifacio, P.; Molaro, P.; Nordström, B.; Primas, F. Bibcode: 2007A&A...476..935F Altcode: 2007arXiv0709.3454F Context: Extremely metal-poor (EMP) stars in the halo of the Galaxy are sensitive probes of the production of the first heavy elements and the efficiency of mixing in the early interstellar medium. The heaviest measurable elements in such stars are our main guides to understanding the nature and astrophysical site(s) of early neutron-capture nucleosynthesis.
Aims: Our aim is to measure accurate, homogeneous neutron-capture element abundances for the sample of 32 EMP giant stars studied earlier in this series, including 22 stars with [Fe/H]< -3.0.
Methods: Based on high-resolution, high S/N spectra from the ESO VLT/UVES, 1D, LTE model atmospheres, and synthetic spectrum fits, we determine abundances or upper limits for the 16 elements Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, and Yb in all stars.
Results: As found earlier, [Sr/Fe], [Y/Fe], [Zr/Fe] and [Ba/Fe] are below Solar in the EMP stars, with very large scatter. However, we find a tight anti-correlation of [Sr/Ba], [Y/Ba], and [Zr/Ba] with [Ba/H] for -4.5 <[Ba/H] < -2.5, also when subtracting the contribution of the main r-process as measured by [Ba/H]. Spectra of even higher S/N ratio are needed to confirm and extend these results below [Fe/H] ≃ -3.5. The huge, well-characterised scatter of the [n-capture/Fe] ratios in our EMP stars is in stark contrast to the negligible dispersion in the [ α/Fe] and [Fe-peak/Fe] ratios for the same stars found in Paper V.
Conclusions: These results demonstrate that a second (“weak” or LEPP) r-process dominates the production of the lighter neutron-capture elements for [Ba/H] < -2.5. The combination of very consistent [ α/Fe] and erratic [n-capture/Fe] ratios indicates that inhomogeneous models for the early evolution of the halo are needed. Our accurate data provide strong constraints on future models of the production and mixing of the heavy elements in the early Galaxy.

Based on observations made with the ESO Very Large Telescope at Paranal Observatory, Chile (program ID 165.N-0276(A); P.I: R. Cayrel). Title: Line shift, line asymmetry, and the ^6Li/^7Li isotopic ratio determination Authors: Cayrel, R.; Steffen, M.; Chand, H.; Bonifacio, P.; Spite, M.; Spite, F.; Petitjean, P.; Ludwig, H. -G.; Caffau, E. Bibcode: 2007A&A...473L..37C Altcode: 2007arXiv0708.3819C Context: Line asymmetries are generated by convective Doppler shifts in stellar atmospheres, especially in metal-poor stars, where convective motions penetrate to higher atmospheric levels. Such asymmetries are usually neglected in abundance analyses. The determination of the ^6Li/^7Li isotopic ratio is prone to suffering from such asymmetries, as the contribution of ^6Li is a slight blending reinforcement of the red wing of each component of the corresponding ^7Li line, with respect to its blue wing.
Aims: The present paper studies the halo star HD 74000 and estimates the impact of convection-related asymmetries on the Li isotopic ratio determination.
Methods: Two methods are used to meet this aim. The first, which is purely empirical, consists in deriving a template profile from another element that can be assumed to originate in the same stellar atmospheric layers as Li I, producing absorption lines of approximately the same equivalent width as individual components of the ^7Li I resonance line. The second method consists in conducting the abundance analysis based on NLTE line formation in a 3D hydrodynamical model atmosphere, taking into account the effects of photospheric convection.
Results: The results of the first method show that the convective asymmetry generates an excess absorption in the red wing of the ^7Li absorption feature that mimics the presence of ^6Li at a level comparable to the hitherto published values. This opens the possibility that only an upper limit on ^6Li/^7Li has thus far been derived. The second method confirms these findings.
Conclusions: From this work, it appears that a systematic reappraisal of former determinations of ^6Li abundances in halo stars is warranted.

Based on observations carried out at the European Southern Observatory (ESO), under prog. ID 75.D-0600. Tables 1-3, and additional references are only available in electronic form at http://www.aanda.org Title: Abundances in extremely metal-poor stars: comparison of the trends of abundance ratios in giants and turnoff stars Authors: Spite, Monique; Bonifacio, Piercarlo; Cayrel, Roger; Spite, François; Hill, Vanessa; Andersen, Johannes; Barbuy, Beatriz; Beers, Timothy; Depagne, Eric; François, Patrick; Molaro, Paolo; Nordström, Birgitta; Plez, Bertrand; Primas, Francesca Bibcode: 2007IAUS..239..280S Altcode: No abstract at ADS Title: NLTE determination of the sodium abundance in a homogeneous sample of extremely metal-poor stars Authors: Andrievsky, S. M.; Spite, M.; Korotin, S. A.; Spite, F.; Bonifacio, P.; Cayrel, R.; Hill, V.; François, P. Bibcode: 2007A&A...464.1081A Altcode: 2007astro.ph..1199A Context: Abundance ratios in extremely metal-poor (EMP) stars are a good indication of the chemical composition of the gas in the earliest phases of the Galaxy evolution. It had been found from an LTE analysis that at low metallicity, and in contrast with most of the other elements, the scatter of [Na/Fe] versus [Fe/H] was surprisingly large and that, in giants, [Na/Fe] decreased with metallicity.
Aims: Since it is well-known that the formation of sodium lines is very sensitive to non-LTE effects, to firmly establish the behaviour of the sodium abundance in the early Galaxy, we have used high quality observations of a sample of EMP stars obtained with UVES at the VLT, and we have taken into account the non-LTE line formation of sodium.
Methods: The profiles of the two resonant sodium D lines (only these sodium lines are detectable in the spectra of EMP stars) have been computed in a sample of 54 EMP giants and turn-off stars (33 of them with [Fe/H]<-3.0) with a modified version of the code MULTI, and compared to the observed spectra.
Results: With these new determinations in the range {-4 <[Fe/H]< -2.5}, both [Na/Fe] and [Na/Mg] are almost constant with a low scatter. In the turn-off stars and "unmixed" giants (located in the low RGB): [Na/Fe] = -0.21 ± 0.13 or [Na/Mg] = -0.45 ± 0.16. These values are in good agreement with the recent determinations of [Na/Fe] and [Na/Mg] in nearby metal-poor stars. Moreover we confirm that all the sodium-rich stars are "mixed" stars (i.e., giants located after the bump, which have undergone an extra mixing). None of the turn-off stars is sodium-rich. As a consequence it is probable that the sodium enhancement observed in some mixed giants is the result of a deep mixing. Title: First stars VII - Lithium in extremely metal poor dwarfs Authors: Bonifacio, P.; Molaro, P.; Sivarani, T.; Cayrel, R.; Spite, M.; Spite, F.; Plez, B.; Andersen, J.; Barbuy, B.; Beers, T. C.; Depagne, E.; Hill, V.; François, P.; Nordström, B.; Primas, F. Bibcode: 2007A&A...462..851B Altcode: 2006astro.ph.10245B Context: The primordial lithium abundance is a key prediction of models of big bang nucleosynthesis, and its abundance in metal-poor dwarfs (the Spite plateau) is an important, independent observational constraint on such models.
Aims: This study aims to determine the level and constancy of the Spite plateau as definitively as possible from homogeneous high-quality VLT-UVES spectra of 19 of the most metal-poor dwarf stars known.
Methods: Our high-resolution (R∼ 43 000), high S/N spectra are analysed with OSMARCS 1D LTE model atmospheres and turbospectrum synthetic spectra to determine effective temperatures, surface gravities, and metallicities, as well as Li abundances for our stars.
Results: Eliminating a cool subgiant and a spectroscopic binary, we find 8 stars to have -3.5 < [Fe/H] < -3.0 and 9 stars with -3.0 < [Fe/H] < -2.5. Our best value for the mean level of the plateau is A(Li) =2.10± 0.09. The scatter around the mean is entirely explained by our estimate of the observational error and does not allow for any intrinsic scatter in the Li abundances. In addition, we conclude that a systematic error of the order of 200 K in any of the current temperature scales remains possible. The iron excitation equilibria in our stars support our adopted temperature scale, which is based on a fit to wings of the Hα line, and disfavour hotter scales, which would lead to a higher Li abundance, but fail to achieve excitation equilibrium for iron.
Conclusions: We confirm the previously noted discrepancy between the Li abundance measured in extremely metal-poor turnoff stars and the primordial Li abundance predicted by standard Big-Bang nucleosynthesis models adopting the baryonic density inferred from WMAP. We discuss recent work explaining the discrepancy in terms of diffusion and find that uncertain temperature scales remain a major question.

Based on observations made with the ESO Very Large Telescope at Paranal Observatory, Chile (Large Programme “First Stars”, ID 165.N-0276(A); P.I. R. Cayrel). Tables 4-8 and Appendix A are only available in electronic form at http://www.aanda.org Title: First stars X. The nature of three unevolved carbon-enhanced metal-poor stars Authors: Sivarani, T.; Beers, T. C.; Bonifacio, P.; Molaro, P.; Cayrel, R.; Herwig, F.; Spite, M.; Spite, F.; Plez, B.; Andersen, J.; Barbuy, B.; Depagne, E.; Hill, V.; François, P.; Nordström, B.; Primas, F. Bibcode: 2006A&A...459..125S Altcode: 2006astro.ph..8112S Context: .On the order of 20% of the very metal-poor stars in the Galaxy exhibit large carbon enhancements. It is important to establish which astrophysical sites and processes are responsible for the elemental abundance patterns of this early Galactic population.
Aims: .We seek to understand the nature of the progenitors of three main-sequence turnoff Carbon-Enhanced Metal-Poor (CEMP) stars, CS 31080-095, CS 22958-042, and CS 29528-041, based on a detailed abundance analysis.
Methods: .From high-resolution VLT/UVES spectra (R∼ 43 000), we determine abundances or upper limits for Li, C, N, O, and other important elements, as well as 12C/13C isotopic ratios.
Results: .All three stars have -3.30 ≤ [Fe/H] ≤ -2.85 and moderate to high CNO abundances. CS 22958-042 is one of the most carbon-rich CEMP stars known ([ C/Fe] = +3.2), while CS 29528-041 (one of the few N-enhanced metal-poor stars known) is one of the most nitrogen rich ([ N/Fe] = +3.0). Oxygen is very high in CS 31080-095 ([ O/Fe] = +2.35) and in CS 22958-042 ([ O/Fe] = +1.35). All three stars exhibit [ Sr/Fe] < 0; Ba is not detected in CS 22958-042 ([ Ba/Fe] < -0.53), but it is moderately enhanced ([ Ba/Fe] ∼ 1) in the other two stars. CS 22958-042 displays one of the largest sodium overabundances yet found in CEMP stars ([ Na/Fe] = +2.8). CS 22958-042 has 12C/13C = 9, similar to most other CEMP stars without enhanced neutron-capture elements, while 12C/13C ≥ 40 in CS 31080-095. CS 31080-095 and CS 29528-041 have A(Li) ∼ 1.7, below the Spite Plateau, while Li is not detected in CS 22958-042.
Conclusions: .CS 22958-042 is a CEMP-no star, but the other two stars are in no known class of CEMP star and thus either constitute a new class or are a link between the CEMP-no and CEMP-s classes, adding complexity to the abundance patterns for CEMP stars. We interpret the abundance patterns in our stars to imply that current models for the presumed AGB binary progenitors lack an extra-mixing process, similar to those apparently operating in RGB stars. Title: The oldest stars in the Milky Way Authors: Cayrel, R. Bibcode: 2006RPPh...69.2823C Altcode: In the framework of modern cosmology, the first stars formed in the cores of dark matter overdensities of a few million solar masses (Modot), when small density fluctuations present in the early universe first attained large amplitudes. Then, the Jeans gravitational instability triggered a run-away collapse, enabling these cores to reach stellar densities, provided that the baryonic matter was able to efficiently radiate away the heat gained from gravitational potential energy during the collapse. Thanks to recent enormous progress in knowledge of the microwave cosmological background (in particular observations by the NASA Wilkinson Microwave Anisotropy Probe), the chemical composition of matter produced during primordial nucleosynthesis in the first 15 min after the Big Bang is completely constrained, and one can confidently identify the chemical composition of the matter from which the first stars were born. Stars with such a composition are called, for historical reasons, Population III stars.

The nature of the first stars has aroused the curiosity of theoreticians and observers alike. Important progress has been made on both sides in the last ten years. A brief account of these recent advances is presented here. When and where the first stars formed is now fairly well understood. One major uncertainty that remains however concerns the distribution of masses of the first stars. It is almost certain that these masses were above the mass required to have such stars still radiating today, i.e. above 0.9 times the mass of the Sun, according to stellar evolution computations. This is unfortunate for observers, who have endeavoured for many decades to find even a single example of a Population III star. However, in the course of their searches, they have at least observed stars with chemical compositions that are very close to the primordial composition. A few stars have been identified, polluted by only 3 × 10-6 in mass by elements not produced by the primordial nucleosynthesis, but by supernova nucleosynthesis. The study of the chemical composition of this tiny fraction of matter is a wonderfully rich source of information on true Population III objects, which synthesized the elements composing it, and then ejected these elements into the surrounding primordial medium, producing the matter from which were born the still observable low-mass stars scrutinized by observers. Title: First stars IX - Mixing in extremely metal-poor giants. Variation of the 12C/13C, [Na/Mg] and [Al/Mg] ratios Authors: Spite, M.; Cayrel, R.; Hill, V.; Spite, F.; François, P.; Plez, B.; Bonifacio, P.; Molaro, P.; Depagne, E.; Andersen, J.; Barbuy, B.; Beers, T. C.; Nordström, B.; Primas, F. Bibcode: 2006A&A...455..291S Altcode: 2006astro.ph..5056S Context: .Extremely metal-poor (EMP) stars preserve a fossil record of the composition of the ISM when the Galaxy formed. It is crucial, however, to verify whether internal mixing has modified their surface composition, especially in the giants where most elements can be studied.
Aims: .We aim to understand the CNO abundance variations found in some, but not all EMP field giants analysed earlier. Mixing beyond the first dredge-up of standard models is required, and its origin needs clarification.
Methods: .The 12C/^{13C} ratio is the most robust diagnostic of deep mixing, because it is insensitive to the adopted stellar parameters and should be uniformly high in near-primordial gas. We have measured 12C and ^{13C} abundances in 35 EMP giants (including 22 with {[Fe/H] < -3.0}) from high-quality VLT/UVES spectra analysed with LTE model atmospheres. Correlations with other abundance data are used to study the depth of mixing.
Results: .The 12C/^{13C} ratio is found to correlate with [C/Fe] (and Li/H), and clearly anti-correlate with [N/Fe], as expected if the surface abundances are modified by CNO processed material from the interior. Evidence for such deep mixing is observed in giants above {log L/L⊙ = 2.6}, brighter than in less metal-poor stars, but matching the bump in the luminosity function in both cases. Three of the mixed stars are also Na- and Al-rich, another signature of deep mixing, but signatures of the ON cycle are not clearly seen in these stars.
Conclusions: .Extra mixing processes clearly occur in luminous RGB stars. They cannot be explained by standard convection, nor in a simple way by rotating models. The Na- and Al-rich giants could be AGB stars themselves, but an inhomogeneous early ISM or pollution from a binary companion remain possible alternatives. Title: Abundance of heavy elements in extremely metal-poor stars Authors: François, P.; Depagne, E.; Hill, V.; Spite, M.; Spite, F.; Plez, B.; Beers, T. C.; Barbuy, B.; Cayrel, R.; Andersen, J.; Bonifacio, P.; Molaro, P.; Nordström, B.; Primas, F. Bibcode: 2006AIPC..847..205F Altcode: This paper reports on the abundance determination of neutron-capture elements in 32 extremely metal-poor stars. The study is based on the analysis of high quality spectra obtained with UVES+Kueyen. The results are compared with the most recent analyses of spectra mostly taken with other 10m class telescopes. Title: The chemical evolution of barium and europium in the Milky Way Authors: Cescutti, G.; François, P.; Matteucci, F.; Cayrel, R.; Spite, M. Bibcode: 2006A&A...448..557C Altcode: 2005astro.ph.10496C Aims.We compute the evolution of the abundances of barium and europium in the Milky Way and we compare our results to the observed abundances from the recent UVES Large Program "First Stars".Methods.We use a chemical evolution model that reproduces the majority of observational constraints.Results.We confirm that barium is a neutron capture element mainly produced in the low mass AGB stars during the thermal-pulsing phase by the 13C neutron source, in a slow neutron capture process. However, in order to reproduce the [Ba/Fe] vs. [Fe/H] as well as the Ba solar abundance, we suggest that Ba is also produced as an r-process element by massive stars in the range 10-30 M⊙. On the other hand, europium should be only an r-process element produced in the same range of masses (10-30 M⊙), at variance with previous suggestions indicating a smaller mass range for the Eu producers. As it is well known, there is a large spread in the [Ba/Fe] and [Eu/Fe] ratios at low metallicities, although smaller in the newest data. With our model we estimate for both elements (Ba and Eu) the ranges for the r-process yields from massive stars that better reproduce the trend of the data. We find that with the same yields able to explain the observed trends, the large spread in the [Ba/Fe] and [Eu/Fe] ratios cannot be explained even in the context of an inhomogeneous models for the chemical evolution of our Galaxy. We therefore derive the amount by which the yields should be modified to fully account for the observed spread. We then discuss several possibilities to explain the size of the spread. We suggest that the production ratio of [Ba/Eu] could be almost constant in massive stars. Title: Sulphur in the Early Ages of the Galaxy Authors: Depagne, E.; Hill, V.; Spite, M.; François, P.; Spite, F.; Plez, B.; Beers, T. C.; Barbuy, B.; Cayrel, R.; Andersen, J.; Bonifacio, P.; Nordström, B.; Primas, F. Bibcode: 2006cams.book..128D Altcode: We present here the results of the measurement of the sulphur abundance in very metal-poor stars. Our sample covers the [-4;-2] range of metallicity, and thus allows us to constraint the chemical evolution models and also to put some key constraints on the supernovae models. Title: Evidence of Mixing in Extremely Metal-Poor Giants Authors: Spite, M.; Cayrel, R.; Spite, F.; Hill, V.; François, P.; Depagne, E.; Barbuy, B.; Bonifacio, P.; Molaro, P.; Primas, F.; Beers, T.; Plez, B.; Nordström, B.; Andersen, J. Bibcode: 2006cams.book..200S Altcode: Thirty five extremely metal-poor (EMP) giants (22 of them with a metallicity [Fe/H] ≤ -3.0) have been observed with UVES at the VLT. In these stars the abundance of lithium carbon and nitrogen and also the 12C/13C ratio have been measured. It is shown that, in about half of them, the carbon abundance and the lithium abundance are very low, on the contrary the nitrogen abundance is high. Moreover the value of the 12C/13C ratio is close to the equilibrium value of the CN cycle. All these phenomena imply a mixing between the surface of the star and the H burning layers. We also study the influence of the mixing on the oxygen, sodium and aluminum abundance. Title: Constraints on the yields of the first supernovae in the Universe Authors: Cayrel, Roger Bibcode: 2006isna.confE.207C Altcode: 2006PoS....28E.207C The study of the chemical composition of the most primitive stars of the galactic halo has been made possible with the help of large surveys aimed at finding such stars, and by powerful new instruments, as the Keck telescopes, the Subaru telescope, and the ESO Very Large Telescope. The atmospheres of these primitive stars possess, per hydrogen atom, from 1/1000th to 1/10000th less supernovae-made elements than the Sun, and reflect the yields of the first supernovae. It was once expected that these yields would show a larger scatter than those in the more metal-rich Population II stars, which have been enriched by many more supernovae explosions than the earlier generations. If we leave aside one class of objects, the Carbon-Enhanced Metal-Poor (CEMP) stars, which is the topic of another talk at this conference, a rather well-defined set of abundance ratios emerge for C to Zn amongst the most primitive population, with a scatter that is surprisingly small. The quality of the high-resolution spectroscopic data is such that the observed level of scatter in the measured elemental abundances for these species is no longer limited by accuracy of the observations, nor by other errors inherent to the analysis of the data. By way of contrast, amongst the neutron-capture elements produced by the r-process, at a given metallicity a spread reaching a factor of over 1000 exists for elements such as Ba. The stable portion of the r-process pattern observed in such stars is the second peak (Z = 56 to 72), in which the relative abundances of these elements in very metal-poor stars are almost indistinguishable from their inferred proportions in solar-system material. Recent observations have permitted the determination of the abundances of uranium, tho- rium, and lead produced by the r-process in extremely metal-poor stars, and indicate that lead is mainly produced by radioactive decay of the actinides (as opposed to other direct channels). In addition, the observed U/Th ratio has been shown to be the best available radioactive cosmic chronometer, on timescales of interest to cosmology. Title: First Stars: Abundance Patterns from O to Zn and Derived SNe Yields in the Early Galaxy Authors: Cayrel, R.; Spite, M. Bibcode: 2006cams.book..114C Altcode: Most of the work reported here has been conducted within the ESO Large Programme 165.N-0276 "Galaxy Formation, Early Nucleosynthesis, and the First Stars", which has covered 4 periods 65-68, from April 2000 to November 2001, with a total of 38 nights in visitor mode. The team had R. Cayrel as PI, and 13 CoIs: Title: Abundance of Heavy Elements in Extremely Metal-Poor Stars Authors: François1, P.; Cayrel, R.; Depagne, E.; Spite, M.; Hill, V.; Spite, F.; Plez, B.; Beers, T.; Primas, F.; Andersen, J.; Barbuy, B.; Bonifacio, P.; Molaro, P.; Nordström, B. Bibcode: 2006cams.book..122F Altcode: In the framework of the VLT Large program "First Stars" (165.N-0276(A)), we have measured the abundance of 13 heavy elements using high quality UVES spectra. In this paper, we report on the abundance of Sr and Ba in this sample of stars. In 1995, McWilliam et al. [4] showed that the [Sr/Fe] and [Ba/Fe] ratios exhibited a large dispersion in metal-poor stars. If these 2 elements are produced by the same nucleosynthetic process, then the variation of [Sr/Ba] as a function of metallicity should be constant . However, it is known (see Arlandini et al. 1999 [1] for example) that a significant part of Sr is built by s-process in massive stars. As this process is a secondary process, it is unlikely that this process is fully in operation at the early stages of the chemical evolution. On figure 1a, the [Sr/Ba] vs [Fe/H] are plotted together with some data found in the literature. Title: Les premieres etoiles ne sont plus la... Authors: Cayrel, R. Bibcode: 2006LAstr.120..216C Altcode: No abstract at ADS Title: ``First Stars, First Nucleosynthesis", New results and a few Perspectives Authors: Spite, M.; Cayrel, R.; Hill, V.; Plez, B.; François, P.; Spite, F.; Depagne, E. Bibcode: 2005sf2a.conf...65S Altcode: We present here briefly some results of the project ``First Stars" and in particular the comparison between extremely metal-poor turn off stars and giants of the low Red Giant Branch which were supposed to be free from any substantial mixing with the H burning layer. The observations suggest more mixing in the low RGB stars than predicted by the models. Title: Very metal poor stars in the Milky Way: constraints on stellar nucleosynthesis Authors: Chiappini, C.; Matteucci, F.; François, P.; Cayrel, R.; Spite, M.; Spite, F. Bibcode: 2005NuPhA.758..217C Altcode: Recently Cayrel et al. [Cayrel, R., Depagne, E., Spite, M. et al. 2004, AfeA 416, 1117] have derived the abundances of several a and Fe-peak elements for a sample of very metal poor giants ([Fe/H] from -4.0 to -3.0 dex) thus allowing us to test chemical evolution models in a metallicity range never reached before. Moreover, the small spread in the [el/Fe] ratios in the metallicity range from [Fe/H]=-4.0 up to -3.0 dex [Cayrel, R., Depagne, E., Spite, M. et al. 2004, AfeA 416, 1117] is a clear sign that the halo of the Milky Way was well mixed even in the earliest phases of its evolution. We computed the evolution of the abundances of O, Mg, Si, Ca, K, Ti, Sc, Ni, Mn, Co, Fe and Zn in the Milky Way. We made use of the most widely adopted nucleosynthesis calculations and compared the model results with observational data with the aim of imposing constraints upon stellar yields. Title: Astrophysics: Two's company Authors: Cayrel, Roger Bibcode: 2005Natur.434..838C Altcode: The matter from which the first stars formed was that left behind by the Big Bang. Stars containing extremely small amounts of heavy elements such as iron provide clues to the chemical composition of this matter. Title: First stars VI - Abundances of C, N, O, Li, and mixing in extremely metal-poor giants. Galactic evolution of the light elements Authors: Spite, M.; Cayrel, R.; Plez, B.; Hill, V.; Spite, F.; Depagne, E.; François, P.; Bonifacio, P.; Barbuy, B.; Beers, T.; Andersen, J.; Molaro, P.; Nordström, B.; Primas, F. Bibcode: 2005A&A...430..655S Altcode: 2004astro.ph..9536S We have investigated the poorly-understood origin of nitrogen in the early Galaxy by determining N abundances from the NH band at 336 nm in 35 extremely metal-poor halo giants, with carbon and oxygen abundances from Cayrel et al. (\cite{CDS04}, A&A, 416, 1117), using high-quality ESO VLT/UVES spectra (30 of our 35 stars are in the range -4.1 < [Fe/H] < -2.7 and 22 stars have [Fe/H] < -3.0). N abundances derived both from the NH band and from the CN band at 389 nm for 10 stars correlate well, but show a systematic difference of 0.4 dex, which we attribute to uncertainties in the physical parameters of the NH band (line positions, gf values, dissociation energy, etc.). Because any dredge-up of CNO processed material to the surface may complicate the interpretation of CNO abundances in giants, we have also measured the surface abundance of lithium in our stars as a diagnostic of such mixing. Our sample shows a clear dichotomy between two groups of stars. The first group shows evidence of C to N conversion through CN cycling and strong Li dilution, a signature of mixing; these stars are generally more evolved and located on the upper Red Giant Branch (RGB) or Horizontal Branch (HB). The second group has [N/Fe] < 0.5, shows no evidence for C to N conversion, and Li is only moderately diluted; these stars belong to the lower RGB and we conclude that their C and N abundances are very close to those of the gas from which they formed in the early Galaxy, they are called ``unmixed stars''. The [O/Fe] and [(C+N)/Fe] ratios are the same in the two groups, confirming that the differences between them are caused by dredge-up of CN-processed material in the first group, with negligible contributions from the O-N cycle. The ``unmixed'' stars reflect the abundances in the early Galaxy: the [C/Fe] ratio is constant (about +0.2 dex) and the [C/Mg] ratio is close to solar at low metallicity, favouring a high C production by massive zero-metal supernovae. The [N/Fe] and [N/Mg] ratios scatter widely. Their mean values in each metallicity bin decrease with increasing metallicity, but this trend could be a statistical effect. The larger values of these ratios define a flat upper plateau ([N/Mg] = 0.0, [N/Fe] = +0.1), which could reflect higher values within a wide range of yields of zero-metal SNe II. Alternatively, by analogy with the DLAs, the lower abundances ([N/Mg] = -1.1, [N/Fe] = -0.7) could reflect generally low yields from the first SNe II, the other stars being N enhanced by winds of massive Asymptotic Giant Branch (AGB) stars. Since all the stars show clear [α/Fe] enhancements, they were formed before any significant enrichment of the Galactic gas by SNe Ia, and their composition should reflect the yields of the first SNe II. However, if massive AGB stars or AGB supernovae evolved more rapidly than SNe Ia and contaminated the ISM, our stars would also reflect the yields of these AGB stars. At present it cannot be decided whether primary N is produced primarily in SNe II or in massive AGB stars, or in both. The stellar N abundances and [N/O] ratios are compatible with those found in Damped Lyman-α (DLA) systems. They extend the well-known DLA ``plateau'' at [N/O] ≈ -0.8 to lower metallicities, albeit with more scatter; no star is found below the putative ``low [N/α] plateau'' at [N/O] ≈ -1.55 in DLAs.

Based on observations obtained with the ESO VLT under ESO programme ID 165.N-0276(A). This work has made use of the SIMBAD database. Title: CS 29497-030: lead in the early Galaxy Authors: Sivarani, T.; Bonifacio, P.; Molaro, P.; Cayrel, R.; Spite, M.; Spite, F.; Plez, B.; Andersen, J.; Barbuy, B.; Beers, T. C.; Depagne, E.; Hill, V.; François, P.; Nordström, B.; Primas, F. Bibcode: 2005HiA....13R.589S Altcode: We present the abundance analysis of the star CS29497-030 which displays a low metallicity ([Fe/H]=-2.8) and a large enhancement of the neutron capture elements. The Pb overabundance with respect to iron ([Pb/Fe]=3.5) is the highest to-date among the s-process enhanced very metal poor stars. The abundance analysis provides also a large overabundance of carbon ([C/Fe]=+2.38) nitrogen ([N/Fe]=+1.88) and oxygen ([O/Fe]=+1.67). These abundances result from the analysis of high resolution and high S/N spectra obtained using the UVES spectrograph on the 8.2m VLT-Kueyen telescope in the course of the Large Programme 165.N-0276 P.I. R. Cayrel. The origin of neutron capture elements at low metallicity has for twenty years been thought to be from the r-process only. The occurence of several stars of very low metallicity which exhibit a large overabundance of s-process elements and lead overabundance with respect to the heavy neutron capture elements(e.g Ba La Ce Nd) seems to point unmistakably to an s-process origin. This suggests that the s-process was operating at early times in the Galaxy at least locally. Title: Lithium abundances in extremely metal-poor stars Authors: Bonifacio, P.; Molaro, P.; Sivarani, T.; Spite, M.; Spite, F.; Cayrel, R.; François, P.; Hill, V.; Plez, B.; Beers, T. C.; Andersen, J.; Barbuy, B.; Depagne, E.; Nordström, B.; Primas, F. Bibcode: 2005HiA....13..581B Altcode: In the course of the ESO Large Programme ""First Stars"" we have observed with the UVES spectrograph at the 8.2m Kueyen-VLT telescope more than thirty stars which were classified as Turn-Off based on medium resolution spectra. Effective temperatures for these stars were derived by fitting the ings of the H-alpha lines. The constant lithium abundance found in metal-poor stars is generally understood to have been produced primordially. If this is the case it provides a measure of the baryonic density which may be compared to the valued recently measured from the fluctuations of the cosmic microwave background by the WMAP experiment. Howevere this may not be the case if the Li observed on the surface of these stars has been increased by Galactic production or decreased by atmospheric phenomena such effects could be highlighted by the existence of variations with metallicity and/or effective temperature of the Li abundance. In this poster we report on the measurement of lithium abundances in this unique homogeneous sample of extremely metal poor stars which provides important information on the Li content of the early Galaxy. Title: Lithium abundances in extremely metal-poor unevolved stars Authors: Bonifacio, P.; Molaro, P.; Sivarani, T.; Cayrel, R.; Spite, M.; Spite, F.; Plez, B.; Andersen, J.; Barbuy, B.; Beers, T. C.; Depagne, E.; Hill, V.; François, P.; Nordström, B.; Primas, F. Bibcode: 2005IAUS..228...35B Altcode: We have studied the lithium abundance in 18 extremely metal-poor main-sequence turnoff stars as a function of [Fe/H] and Teff, using high-quality VLT/UVES spectra. The sample covers the range -3.3≤ [{Fe}/{H}]≤ -2.5, with half of the stars below [Fe/H] = -3.0. Teff is determined from Hα 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. Title: A Tribute to Monique and François Spite Authors: Cayrel, R. Bibcode: 2005IAUS..228....3C Altcode: This contribution retraces the scientific careers of Monique and François. It highlights the impressive contributions that they have brought to astrophysics, from the discovery of the lithium plateau in subdwarfs the second year of operation of the Canada-France-Hawaii telescope, to the exceptional contribution of Monique to the ESO VLT Large Programme "First Stars", passing by several other findings which have marked our knowledge of the nuclear evolution of our Galaxy and of the Magellanic Clouds. Title: Heavy elements in a sample of extremely metal-poor giants Authors: François, P.; Depagne, E.; Cayrel, R.; Hill, V.; Spite, F.; Spite, M.; Plez, B.; Barbuy, B.; Beers, T.; Bonifacio, P.; Andersen, J.; Primas, F.; Sivarani, T.; Nordström, B.; Molaro, P. Bibcode: 2005HiA....13R.583F Altcode: The abundances of the neutron capture elements (Sr Ba La Ce Eu [Truncated.] Title: Abundances in extremely metal-poor stars. Comparison of the trends of abundance ratios in giants and turnoff stars Authors: Spite, Monique; Bonifacio, Piercarlo; Cayrel, Roger; Hill, Vanessa; François, Patrick; Spite, François; Plez, Bertrand; Depagne, Eric; Barbuy, Beatriz; Molaro, Paolo; Beers, Timothy; Andersen, Johannes; Nordström, Birgitta; Primas, Francesca Bibcode: 2005IAUS..228..185S Altcode: As part of a study of the detailed abundance patterns in extremely metal-poor stars, we have compared our samples of giants and dwarfs with two samples of dwarfs measured by different teams. For most elements the abundances are in good agreement, but for C, Na, and Al we show that the atmospheric abundances are different in dwarfs and in giants. For C the difference could be explained by "atmospheric effects" or by the influence of the first dredge-up, but for Na and Al deep mixing inside the stars must be invoked. Until now, such deep mixing has not been observed in metal-poor field stars. An excess scatter in [Mg/Fe] in giants remains unexplained. Title: Oxygen abundance and convection Authors: van't Veer, C.; Cayrel, R. Bibcode: 2005HiA....13..152V Altcode: No abstract at ADS Title: Evolution of the abundances of the light elements C, Mg, Al in the amosphere of extremely metal-poor stars ( [Fe/H] ⪉ -3) Authors: Spite, M.; Cayrel, R.; Spite, F.; Hill, V.; Francois, P.; Plez, B.; Depagne, E. Bibcode: 2005EAS....17..353S Altcode: 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 the atmospheres of the extremely metal poor stars varies when the star evolves. This could be explained by a mixing with deep layers but such a mixing is not predicted by the theory. Title: Abundance of nitrogen in the early Galaxy from the NH band at 336nm Authors: Spite, M.; Plez, B.; Hill, V.; Spite, F.; Cayrel, R.; François, P.; Depagne, E.; Andersen, J.; Barbuy, B.; Beers, T.; Bonifacio, P.; Molaro, P.; Nordström, B.; Primas, F. Bibcode: 2005HiA....13..590S Altcode: In the frame of the ESO Large Program ""First Stars"" spectra of about 40 extremely metal-poor giants ([Fe/H]<-2.7) have been obtained with UVES at the VLT in the range 330-900 nm. The behaviour of nitrogen at low metallicity is up to now badly known. We present here a first estimation of the nitrogen abundance in these extremely metal-poor stars from a synthesis of the spectrum in the region of the NH band between 336 and 337nm. The trend of [N/Fe] but also of [C+N/Fe] versus metallicity are presented and discussed. Title: Constraints on early galactic enrichment from a large sample of extremely metal-poor stars observed with VLT+UVES Authors: Hill, V.; Cayrel, R.; Spite, M.; Plez, B.; Spite, F.; François, P.; Depagne, E.; Andersen, J.; Barbuy, B.; Beers, T.; Bonifacio, P.; Molaro, P.; Nordström, B.; Primas, F. Bibcode: 2005HiA....13Q.584H Altcode: Constraints on Early Galactic Enrichement from a large sample of Extremely Metal Poor Stars

I will present the overall results from an large effort conducted at ESO-VLT+UVES to measure abundances in a sample of extremely metal-poor stars (EMPS) from high-resolution and high signal to noise spectra. More than 70 EMPS with [Fe/H]<-2.7 were observed equally distributed between turnoff and giants stars and very precise abundance ratios could be derived thanks to the high quality of the data. Among the results those of specific interest are lithium measurements in unevolved EMPS the much debated abundance of oxygen in the early galaxy (we present [OI] line measurements down to [O/Fe]=-3.5) and the trends of alpha elements iron group elements and Zinc. The scatter around these trends will also be discussed taking advantage of the small observationnal error-bars of this dataset. The implications on the early Galactic enrichement will be rewiewed while more specific topics covered by this large effort (and large team) will be adressed in devoted posters. Title: General discussion III: Chemistry and self-pollution mechanisms Authors: Cayrel, R. Bibcode: 2005HiA....13..157C Altcode: No abstract at ADS Title: New analysis of the two carbon-rich stars CS 22948-27 and CS 29497-34: Binarity and neutron capture elements Authors: Barbuy, B.; Spite, M.; Spite, F.; Hill, V.; Cayrel, R.; Plez, B.; Petitjean, P. Bibcode: 2005A&A...429.1031B Altcode: 2004astro.ph..9213B We have carried out a new determination of abundances in the very metal-poor CH/CN strong stars CS 22948-27 and CS 29497-34, using high-resolution spectra obtained with the HARPS spectrograph at the 3.6 m telescope of ESO, La Silla, that covers the range λλ 4000-6900 Å at a resolution of R = 100 000. Both stars are found to be long period binaries. It is confirmed that the abundance patterns show an enhancement of the α-elements (like Mg, Ca), of the proton capture elements (like Na and Al) and a strong enrichment in ``r'' and ``s'' process elements, where the s-enrichment is probably due to a mass transfer episode from a companion in its AGB phase. The possible origins of the abundance pattern and especially of the strong enhancement of both ``s'' and ``r'' elements are discussed.

Observations collected at the European Southern Observatory (ESO), ESO Programme 72.A-0244 (PI Petitjean), and including data obtained from the ESO/ST-ECF Science Archive Facility. Title: Lead abundance in the uranium star CS 31082-001 Authors: Plez, B.; Hill, V.; Cayrel, R.; Spite, M.; Barbuy, B.; Beers, T. C.; Bonifacio, P.; Primas, F.; Nordström, B. Bibcode: 2004A&A...428L...9P Altcode: 2004astro.ph.10628P In a previous paper we were able to measure the abundance of uranium and thorium in the very-metal poor halo giant BPS CS 31082-001, but only obtained an upper limit for the abundance of lead (Pb). We have got from ESO 17 h of additional exposure on this star in order to secure a detection of the minimum amount of lead expected to be present in CS 31082-001, the amount arising from the decay of the original content of Th and U in the star. We report here this successful detection. We find an LTE abundance log(Pb/H)+12=-0.55 ± 0.15 dex, one dex below the upper limits given by other authors for the similar stars CS 22892-052 and BD +17°3248, also enhanced in r-process elements. From the observed present abundances of Th and U in the star, the expected amount of Pb produced by the decay of 232Th, and 238U alone, over 12-15 Gyr is -0.73± 0.17 dex. The decay of 235U is more difficult to estimate, but is probably slightly below the contribution of 238U, making the contribution of the 3 actinides only slightly below, or even equal to, the measured abundance. The contribution from the decay of 234U has was not included, for lack of published data. In this sense our determination is a lower limit to the contribution of actinides to lead production. We comment this result, and we note that if a NLTE analysis, not yet possible, doubles our observed abundance, the decay of the 3 actinides will still represent 50 per cent of the total lead, a proportion higher than the values considered so far in the literature.

Based on observations obtained with the Very Large Telescope of the European Southern Observatory at Paranal, Chile. Title: The First Stars: What We Know and Do Not Know Authors: Cayrel, R.; Spite, M. Bibcode: 2004Msngr.118...55C Altcode: The H and K survey of Beers, Preston & Shectman has been the mine of extremely metal-poor stars during the last decade of the XXth century. The VLT-UVES combination has allowed us to study the chemical composition of the brightest members of this population, fossil component of events which have occured either during the formation of the galaxy, or earlier in smaller systems having eventually merged into our beautiful milky way. We report here what has been derived from a VLT large programme devoted to these objects, as well as on other questions relevant to the first stars. Title: The evolution of the Milky Way from its earliest phases: Constraints on stellar nucleosynthesis Authors: François, P.; Matteucci, F.; Cayrel, R.; Spite, M.; Spite, F.; Chiappini, C. Bibcode: 2004A&A...421..613F Altcode: 2004astro.ph..1499F We computed the evolution of the abundances of O, Mg, Si, Ca, K, Ti, Sc, Ni, Mn, Co, Fe and Zn in the Milky Way. We made use of the most widely adopted nucleosynthesis calculations and compared the model results with observational data with the aim of imposing constraints upon stellar yields. To best fit the data in the solar neighborhood, when adopting the Woosley & Weaver (1995, ApJS, 101, 181) yields for massive stars and the Iwamoto et al. (\cite{Iwamoto99}, ApJS, 125, 439) ones for type Ia SNe, it is required that: i) the Mg yields should be increased in stars with masses from 11 to 20 M⊙ and decreased in masses larger than 20 M⊙. The Mg yield should be also increased in SNe Ia. ii) The Si yields should be slightly increased in stars above 40 M⊙, whereas those of Ti should be increased between 11 and 20 M⊙ and above 30 M⊙. iii) The Cr and Mn yields should be increased in stars with masses in the range 11-20 M⊙; iv) the Co yields in SNe Ia should be larger and smaller in stars in the range 11-20 M⊙; v) the Ni yield from type Ia SNe should be decreased; vi) the Zn yield from type Ia SNe should be increased. vii) The yields of O (metallicity dependent SN models), Ca, Fe, Ni, and Zn (the solar abundance case) in massive stars from Woosley & Weaver (\cite{Woosley95}) are the best to fit the abundance patterns of these elements since they do not need any changes. We also adopted the yields by Nomoto et al. (\cite{Nomoto97}, Nucl. Phys. A, 621, 467) and Limongi & Chieffi (\cite{Limongi03}, ApJ, 592, 404) for massive stars and discuss the corrections required in these yields in order to fit the observations. Finally, the small spread in the [el/Fe] ratios in the metallicity range from [Fe/H] = -4.0 up to -3.0 dex (Cayrel et al. \cite{Cayrel03}, A&A, 416, 1117) is a clear sign that the halo of the Milky Way was well mixed even in the earliest phases of its evolution. Title: First stars V - Abundance patterns from C to Zn and supernova yields in the early Galaxy Authors: Cayrel, R.; Depagne, E.; Spite, M.; Hill, V.; Spite, F.; François, P.; Plez, B.; Beers, T.; Primas, F.; Andersen, J.; Barbuy, B.; Bonifacio, P.; Molaro, P.; Nordström, B. Bibcode: 2004A&A...416.1117C Altcode: 2003astro.ph.11082C In the framework of the ESO Large Programme ``First Stars'', very high-quality spectra of some 70 very metal-poor dwarfs and giants were obtained with the ESO VLT and UVES spectrograph. These stars are likely to have descended from the first generation(s) of stars formed after the Big Bang, and their detailed composition provides constraints on issues such as the nature of the first supernovae, the efficiency of mixing processes in the early Galaxy, the formation and evolution of the halo of the Galaxy, and the possible sources of reionization of the Universe. This paper presents the abundance analysis of an homogeneous sample of 35 giants selected from the HK survey of Beers et al. (\cite{BPS92}, \cite{Be99}), emphasizing stars of extremely low metallicity: 30 of our 35 stars are in the range -4.1 <[Fe/H]< -2.7, and 22 stars have [Fe/H] < -3.0. Our new VLT/UVES spectra, at a resolving power of R∼45 000 and with signal-to-noise ratios of 100-200 per pixel over the wavelength range 330-1000 nm, are greatly superior to those of the classic studies of McWilliam et al. (\cite{MPS95}) and Ryan et al. (\cite{RNB96}).

The immediate objective of the work is to determine precise, comprehensive, and homogeneous element abundances for this large sample of the most metal-poor giants presently known. In the analysis we combine the spectral line modeling code ``Turbospectrum'' with OSMARCS model atmospheres, which treat continuum scattering correctly and thus allow proper interpretation of the blue regions of the spectra, where scattering becomes important relative to continuous absorption (λ < 400 nm). We obtain detailed information on the trends of elemental abundance ratios and the star-to-star scatter around those trends, enabling us to separate the relative contributions of cosmic scatter and observational/analysis errors.

Abundances of 17 elements from C to Zn have been measured in all stars, including K and Zn, which have not previously been detected in stars with [Fe/H] < -3.0. Among the key results, we discuss the oxygen abundance (from the forbidden [OI] line), the different and sometimes complex trends of the abundance ratios with metallicity, the very tight relationship between the abundances of certain elements (e.g., Fe and Cr), and the high [Zn/Fe] ratio in the most metal-poor stars. Within the error bars, the trends of the abundance ratios with metallicity are consistent with those found in earlier literature, but in many cases the scatter around the average trends is much smaller than found in earlier studies, which were limited to lower-quality spectra. We find that the cosmic scatter in several element ratios may be as low as 0.05 dex.

The evolution of the abundance trends and scatter with declining metallicity provides strong constraints on the yields of the first supernovae and their mixing into the early ISM. The abundance ratios found in our sample do not match the predicted yields from pair-instability hypernovae, but are consistent with element production by supernovae with progenitor masses up to 100 M⊙. Moreover, the composition of the ejecta that have enriched the matter

Based on observations obtained in the frame of the ESO programme ID 165.N-0276(A).

Full Tables 3 and 8 are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/416/1117 This work has made use of the SIMBAD database. Title: Oxygen abundance and convection Authors: Van't Veer, C.; Cayrel, R. Bibcode: 2004MmSAI..75..310V Altcode: The triplet IR lines of O I near 777 nm are computed with the Kurucz's code, modified to accept several convection models. The program has been run with the MLT algorithm, with l/H = 1.25 and 0.5, and with the Canuto-Mazzitelli and Canuto-Goldman-Mazzitelli approaches, on a metal-poor turnoff-star model atmosphere with Teff=6200 K, log g = 4.3, [Fe/H]= -1.5. The results show that the differences in equivalent widths for the 4 cases do not exceed 2 per cent (0.3 mA). The convection treatment is therefore not an issue for the oxygen abundance derived from the permitted lines. Title: General Discussion III: Chemistry and Self-Pollution Mechanisms Authors: Cayrel, R. Bibcode: 2004MmSAI..75..385C Altcode: Round table 3 was devoted to the origin of chemical anomalies found in a significant fraction of stars in GCs, but not in field metal-poor stars of similar metallicity. Formerly a hot topic was if such anomalies, studied only in giant stars, bright enough to allow reliable abundance determinations, were generated in the course of the evolution of the star, or inherited at the birth of the star. The ESO Large Program led by R. Gratton has demonstrated, without ambiguity, that the most famous of these ``anomalies'', the O-Na anticorrelation, was already present in turn-off (TO) stars, therefore already there at the birth of the star.

This does not preclude that some modifications occur along the red giant branch, as described for example already in Charbonnel (1994), but those are well identified and do not include the O-Na anticorrelation, but affect mostly 12C,13C, 14N and Li.* More recently, models including rotation in the evolution ( see for example talks by Charbonnel and Weiss at JD 4) have been produced. The most promising process for explaining the O-Na anticorrelation is the hot-bottom-burning process (HBB) in TP-AGBs, Ventura et al. (2001). The problem remaining is the transfer of the processed matter to an unevolved star. Here, several routes exist, and so far no consensus has been reached on those which are dominant.

Roundtable 3 was expected to supply a live discussion between the proponents of the various ideas emitted on this subject. Unfortunately, in the time allotted, the only thing which appeared possible was to suggest tests for evaluating the coherence of the various proposals, against the widest set of observational constraints. For example, the HBB produces an enrichment in helium, potentially affecting the isochrones. Very accurate observations could try to detect this side-effect. Transfer of mass from an AGB to an unevolved companion is an efficient way of pollution. But it is then expected that the remaining binary shows a variable radial velocity (unless the pair has been disrupted afterwards...). At the other extreme, the mass loss of AGBs may have been large enough to have produced a second generation in a GC ( see F. D'Antona contribution). But let us leave their role to our participants... Title: The Age of the First Nucleosynthesis in the Galaxy Authors: Cayrel, R.; Hill, V.; Spite, M.; Spite, F.; François, P.; Depagne, E.; Nordström, B.; Andersen, J.; Plez, B.; Barbuy, B.; Beers, T.; Bonifacio, P.; Molaro, P.; Primas, F. Bibcode: 2004oee..sympE...9C Altcode: The observation of extremely metal-poor stars makes possible to obtain the epoch of formation of the first elements produced by massive supernovae, or hypernovae. The classical way of obtaining stellar ages (isochrone fitting) is unfortunately not applicable at present, as the distances of these stars are not known with enough accuracy. Dating by decay of radio-elements is another path, which has been renewed by the observation of uranium in the yellow giant CS 31082-001. We discuss the prospects opened by this discovery, and recent theoretical works triggered by this new opportunity. Title: Trends of Abundance in Extremely Metal-poor Giants Observed at the VLT Authors: Spite, M.; Depagne, E.; Cayrel, R.; Hill, V.; François, P.; Spite, F.; Nordström, B.; Andersen, J.; Plez, B.; Barbuy, B.; Beers, T.; Bonifacio, P.; Molaro, P.; Primas, F. Bibcode: 2004oee..sympE..54S Altcode: We present here the first abundance trends from C to Zn deduced from the observation of 33 extremely metal-poor stars selected in the HK survey of Beers et al. (1992). The trends of the abundance ratios of the different elements like [Mg/Fe], [Cr/Fe] are not very different from the trends deduced from the observations of McWilliam et al.(1995), but for several important elements (like Mg, Cr) the spread is much smaller. For almost all the elements the spread increases when the metallicity decreases, this is particularly evident for the trend of [Mn/Fe] versus [Fe/H].

The elements heavier than Zn will be discussed later. Title: First stars IV. CS 29497-030: Evidence for operation of the s-process at very low metallicity Authors: Sivarani, T.; Bonifacio, P.; Molaro, P.; Cayrel, R.; Spite, M.; Spite, F.; Plez, B.; Andersen, J.; Barbuy, B.; Beers, T. C.; Depagne, E.; Hill, V.; François, P.; Nordström, B.; Primas, F. Bibcode: 2004A&A...413.1073S Altcode: 2003astro.ph.10291S We present an abundance analysis of the very metal-poor, carbon-enhanced star CS 29497-030. Our results indicate that this unusually hot turnoff star (Teff = 6650 K, log g = 3.5) has a metallicity [Fe/H] = -2.8, and exhibits large overabundances of carbon ([C/Fe] = +2.38), nitrogen ([N/Fe] = +1.88), and oxygen ([O/Fe] = +1.67). This star also exhibits a large enhancement in its neutron-capture elements; the pattern follows that expected to arise from the s-process. In particular, the Pb abundance is found to be very high with respect to iron ([Pb/Fe] = +3.5), and also with respect to the second peak s-process elements (e.g., Ba, La, Ce, Nd), which fits into the newly introduced classification of lead (Pb) stars. The known spectroscopic binary status of this star, along with the observed s-process abundance pattern, suggest that it has accreted matter from a companion, which formerly was an Asymptotic Giant-Branch (AGB) star. In a preliminary analysis, we have also identified broad absorption lines of metallic species that suggest a large axial rotational velocity for this star, which may be the result of spin-up associated with the accretion of material from its previous AGB companion. In addition, this star is clearly depleted in the light element Li. When considered along with its rather high inferred temperature, these observations are consistent with the expected properties of a very low metallicity halo blue straggler.

Based on observations made with the ESO Very Large Telescope at Paranal Observatory, Chile (program ID 165.N-0276(A)).

Table \ref{tab6} is only available in electronic form at http://www.edpsciences.org Title: VizieR Online Data Catalog: Abundances in the early Galaxy (Cayrel+, 2004) Authors: Cayrel, R.; Depagne, E.; Spite, M.; Hill, V.; Spite, F.; Francois, P.; Plez, B.; Beers, T.; Primas, F.; Andersen, J.; Barbuy, B.; Bonifacio, P.; Molaro, P.; Nordstrom, B. Bibcode: 2003yCat..34161117C Altcode: The observations were performed during several runs from April 2000 to November 2001 with the VLT-UT2 and the high-resolution spectrograph UVES.

(3 data files). Title: First Stars. III. A detailed elemental abundance study of four extremely metal-poor giant stars Authors: François, P.; Depagne, E.; Hill, V.; Spite, M.; Spite, F.; Plez, B.; Beers, T. C.; Barbuy, B.; Cayrel, R.; Andersen, J.; Bonifacio, P.; Molaro, P.; Nordström, B.; Primas, F. Bibcode: 2003A&A...403.1105F Altcode: This paper reports detailed abundance analyses for four extremely metal-poor (XMP) giant stars with [Fe/H]<-3.8, based on high-resolution, high-S/N spectra from the ESO VLT (Kueyen/UVES) and LTE model atmosphere calculations. The derived [alpha /Fe] ratios in our sample exhibit a small dispersion, confirming previous findings in the literature, i.e. a constant overabundance of the alpha -elements with a very small (if any) dependence on [Fe/H]. In particular, the very small scatter we determine for [Si/Fe] suggests that this element shows a constant overabundance at very low metallicity, a conclusion which could not have been derived from the widely scattered [Si/Fe] values reported in the literature for less metal-poor stars. For the iron-peak elements, our precise abundances for the four XMP stars in our sample confirm the decreasing trend of Cr and Mn with decreasing [Fe/H], as well as the increasing trend for Co and the absence of any trend for Sc and Ni. In contrast to the significant spread of the ratios [Sr/Fe] and [Ba/Fe], we find [Sr/Ba] in our sample to be roughly solar, with a much lower dispersion than previously found for stars in the range -3.5 < [Fe/H] < -2.5.

Based on observations made with the ESO Very Large Telescope at Paranal Observatory, Chile (Large Programme ID 165.N-0276(A)).

The complete version of Table 5 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or via http:/ /cdsweb.u-strasbg.fr/cgi-bin/qcat?J /A+A/403/1105 Title: A grid of synthetic spectra and indices Fe5270, Fe5335, Mgb and Mg2 as a function of stellar parameters and [alpha/Fe] Authors: Barbuy, B.; Perrin, M. -N.; Katz, D.; Coelho, P.; Cayrel, R.; Spite, M.; Van't Veer-Menneret, C. Bibcode: 2003A&A...404..661B Altcode: We have computed a grid of synthetic spectra in the wavelength range lambda lambda 4600-5600 Å using revised model atmospheres, for a range of atmospheric parameters and values of [alpha -elements/Fe] = 0.0 and +0.4. The Lick indices Fe5270, Fe5335, Mgb and Mg2 are measured on the grid spectra for FWHM = 2 to 8.3 Å. Relations between the indices Fe5270, Fe5335 and Mg2 and the stellar parameters effective temperature Teff, log ; g, [Fe/H] and [alpha /Fe], valid in the range 4000 <= Teff <= 7000 K, are presented. These fitting functions are given for FWHM = 3.5 and 8.3 Å. The indices were also measured for a list of 97 reference stars with well-known stellar parameters observed at ESO and OHP, and these are compared to the computed indices. Finally, a comparison of the indices measured on the observed spectra and those derived from the fitting functions based on synthetic spectra is presented.

Observations collected at the European Southern Observatory (ESO), La Silla, Chile and at the Observatoire de Haute Provence (OHP), St-Michel, France.

All Tables of Appendices A and B are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?/A+A/404/661 Title: Oxygen Abundance in the Template Halo Giant HD 122563 Authors: Barbuy, Beatriz; Meléndez, Jorge; Spite, Monique; Spite, François; Depagne, Eric; Hill, Vanessa; Cayrel, Roger; Bonifacio, Piercarlo; Damineli, Augusto; Torres, Carlos A. O. Bibcode: 2003ApJ...588.1072B Altcode: HD 122563 is a well-known bright (V=6.2) halo giant of low metallicity ([Fe/H]~-2.7). We have observed HD 122563 for infrared OH lines at 1.5-1.7 μm in the H band with the NIRSPEC high-resolution spectrograph at the 10 m Keck Telescope. Optical spectra were obtained with the UVES spectrograph at the 8 m VLT UT2 telescope at ESO (Paranal) and the FEROS spectrograph at ESO (La Silla). Based on the optical high-resolution data, a detailed analysis has been carried out, and data on the forbidden [O I] 6300 Å line, unblended by telluric or sky lines, was obtained with the FEROS spectrograph. Signal-to-noise ratios of 200-400 were obtained at resolutions of 37,000 in the H band and 45,000 in the optical. For the analysis we have adopted a photometric effective temperature Teff=4600 K. Two values for the gravity were adopted: a value deduced from ionization equilibrium, logg=1.1, with corresponding metallicity [Fe/H]=-2.8 and microturbulence velocity vt=2.0 km s-1; and logg=1.5, derived from the Hipparcos parallax, implying [Fe/H]=-2.71 and vt=2.0 km s-1. The forbidden [O I] 6300 Å and the permitted O I 7771 Å lines give O/Fe ratios essentially insensitive to model parameter variations, whereas the oxygen abundances from OH lines are sensitive to gravity, giving [O/Fe]=+0.9 and +0.7, respectively, for logg=1.1 and 1.5. We derive the following oxygen abundances: for model 1, [O/Fe]=+0.6, +1.1, and +0.9; and for model 2, [O/Fe]=+0.6, +1.1, and +0.7, based on the [O I] 6300 Å, O I 7771 Å, and IR OH 1.6 μm lines, respectively. The different oxygen abundance indicators give different oxygen abundances, illustrating the problem of oxygen abundance derivation in metal-poor giants. This is important because the age of globular clusters and the production of Li, Be, and B from spallation of C, N, and O atoms in the early Galaxy depend on the oxygen abundance adopted for the metal-poor stars.

Observations carried out with the Keck Telescope, Mauna Kea, Hawaii, within the Gemini-Keck agreement, the Very Large Telescope at the European Southern Observatory (ESO), Paranal, Chile, and the 1.5 m ESO telescope at ESO, La Silla, Chile. Title: VizieR Online Data Catalog: Extremely metal-poor giants equivalent widths (Francois+, 2003) Authors: Francois, P.; Depagne, E.; Hill, V.; Spite, M.; Spite, F.; Plez, B.; Beers, T. C.; Barbuy, B.; Cayrel, R.; Andersen, J.; Bonifacio, P.; Molaro, P.; Nordstroem, F.; Primas, B. Bibcode: 2003yCat..34031105F Altcode: The observations were carried out during several observing runs in 2000 and 2001 using the VLT-Kueyen telescope and UVES spectrograph. The log of the observations and spectrograph settings can be found in Table 1.

(1 data file). Title: VizieR Online Data Catalog: Fe5270, Fe5335, Mgb and Mg2 synthetic indices (Barbuy+, Authors: Barbuy, B.; Perrin, M. -N.; Katz, D.; Coelho, P.; Cayrel, R.; Spite, M.; van't Veer Menneret, C. Bibcode: 2003yCat..34040661B Altcode: We have computed a grid of synthetic spectra in the wavelength range λλ4600-5600Å using revised model atmospheres, for a range of atmospheric parameters and values of [alpha-elements/Fe]=0.0 and +0.4. The Lick indices Fe5270, Fe5335, Mgb and Mg2 are measured on the grid spectra, for FWHM=2 to 8.3Å. Relations between the indices Fe5270, Fe5335 and Mg2 and stellar parameters effective temperature Teff, logg, [Fe/H] and [alpha/Fe], valid in the range 4000K>=Teff>=7000K, are presented. These fitting functions are given for FWHM=3.5 and 8.3Å. The indices were also measured for a list of 97 reference stars with well-known stellar parameters observed at ESO and OHP, and these are compared to the computed indices. Finally, a comparison of the indices measured on the observed spectra and those derived from the fitting functions based on synthetic spectra is presented.

(11 data files). Title: Abundance Ratios in a Large Sample of Emps with VLT+UVES Authors: Hill, Vanessa; Cayrel, Roger; Spite, Monique; Bonifacio, Piercarlo; Eric, Depagne; Patrick, François; Timothy, Beers C.; Johannes, Andersen; Beatriz, Barbuy; Birgitta, Nordström Bibcode: 2003IAUJD..15E..13H Altcode: Constraints on Early Galactic Enrichement from a large sample of Extremely Metal Poor Stars

I will present the overall results from an large effort conducted at ESO-VLT+UVES to measure abundances in a sample of extremely metal-poor stars (EMPS) from high-resolution and high signal to noise spectra. More than 70 EMPS with [Fe/H]<-2.7 were observed equally distributed between turnoff and giants stars and very precise abundance ratios could be derived thanks to the high quality of the data. Among the results those of specific interest are lithium measurements in unevolved EMPS the much debated abundance of oxygen in the early galaxy (we present [OI] line measurements down to [O/Fe]=-3.5) and the trends of alpha elements iron group elements and Zinc. The scatter around these trends will also be discussed taking advantage of the small observationnal error-bars of this dataset. The implications on the early Galactic enrichement will be rewiewed while more specific topics covered by this large effort (and large team) will be adressed in devoted posters. Title: CS29497-030: Lead in the Early Galaxy Authors: Sivarani, Thirupathi; Bonifacio, Piercarlo; Molaro, Paolo; Cayrel, Roger; Spite, Monique; Spite, Francois; Plez, Bertrand; Andersen, Johannes; Barbuy, Beatriz; Beers, Timothy C. Bibcode: 2003IAUJD..15E..41S Altcode: We present the abundance analysis of the star CS29497-030 which displays a low metallicity ([Fe/H]=-2.8) and a large enhancement of the neutron capture elements. The Pb overabundance with respect to iron ([Pb/Fe]=3.5) is the highest to-date among the s-process enhanced very metal poor stars. The abundance analysis provides also a large overabundance of carbon ([C/Fe]=+2.38) nitrogen ([N/Fe]=+1.88) and oxygen ([O/Fe]=+1.67). These abundances result from the analysis of high resolution and high S/N spectra obtained using the UVES spectrograph on the 8.2m VLT-Kueyen telescope in the course of the Large Programme 165.N-0276 P.I. R. Cayrel. The origin of neutron capture elements at low metallicity has for twenty years been thought to be from the r-process only. The occurence of several stars of very low metallicity which exhibit a large overabundance of s-process elements and lead overabundance with respect to the heavy neutron capture elements(e.g Ba La Ce Nd) seems to point unmistakably to an s-process origin. This suggests that the s-process was operating at early times in the Galaxy at least locally. Title: Nitrogen Abundance in Extremely Metal-Poor Giants Authors: Spite, Monique; Cayrel, Roger; Plez, Bertrand; Hill, Vanessa; Barbuy, Beatriz; Depagne, Eric; Francois, Patrick; Primas, Francesca; Spite, Francois; Bonifacio, Piercarlo Bibcode: 2003IAUJD..15E..42S Altcode: In the frame of the ESO Large Program ""First Stars"" spectra of about 40 extremely metal-poor giants ([Fe/H]<-2.7) have been obtained with UVES at the VLT in the range 330-900 nm. The behaviour of nitrogen at low metallicity is up to now badly known. We present here a first estimation of the nitrogen abundance in these extremely metal-poor stars from a synthesis of the spectrum in the region of the NH band between 336 and 337nm. The trend of [N/Fe] but also of [C+N/Fe] versus metallicity are presented and discussed. Title: Lithium Abundances in Extremely Metal Poor Stars Authors: Bonifacio, Piercarlo; Molaro, Paolo; Sivarani, Thirupathi; Spite, Monique; Spite, Francois; Cayrel, Roger; Francois, Francois; Hill, Vanessa; Plez, Bertrand; Beers, Timotrhy C. Bibcode: 2003IAUJD..15E..39B Altcode: In the course of the ESO Large Programme ""First Stars"" we have observed with the UVES spectrograph at the 8.2m Kueyen-VLT telescope more than thirty stars which were classified as Turn-Off based on medium resolution spectra. Effective temperatures for these stars were derived by fitting the ings of the H-alpha lines. The constant lithium abundance found in metal-poor stars is generally understood to have been produced primordially. If this is the case it provides a measure of the baryonic density which may be compared to the valued recently measured from the fluctuations of the cosmic microwave background by the WMAP experiment. Howevere this may not be the case if the Li observed on the surface of these stars has been increased by Galactic production or decreased by atmospheric phenomena such effects could be highlighted by the existence of variations with metallicity and/or effective temperature of the Li abundance. In this poster we report on the measurement of lithium abundances in this unique homogeneous sample of extremely metal poor stars which provides important information on the Li content of the early Galaxy. Title: Neutron-Capture Elements in Extremely Metal-Poor Giants Authors: Francois, Patrick; Hill, Vanessa; Cayrel, Roger; Spite, Monique; Spite, Francois; Depagne, Eric; Primas, Francesca; Bonifacio, Piercarlo; Plez, Bertrand; Beers, Tim C. Bibcode: 2003IAUJD..15E..44F Altcode: The abundances of the neutron capture elements (Sr Ba LaCe Eu...) in a sample of more than 30 extremely metal-poor giants ([Fe/H]<-2.7) observed at the VLT with the high resolution spectrograph UVES. The S/N ratio of the spectra is high and it is generally possible to measure very weak lines (W>=1mA). The trends of the ratios [Sr/Fe] [Ba/Fe]... with metallicity are shown and the scatters compared to the scatter observed for iron-peak elements. Consequences for the formation of these elements and the the galactic evolution are discussed. Title: Heavy Elements in a Sample of Extremely Metal-Poor Giants Authors: Francois, Patrick; Depagne, Eric; Cayrel, Roger; Hill, Vanessa; Spite, Francois; Spite, Monique; Plez, Bertrand; Barbuy, Beatriz; Beers, Tim; Bonifacio, Piercarlo Bibcode: 2003IAUJD..15E..55F Altcode: The abundances of the neutron capture elements (Sr Ba La Ce Eu Title: Elemental abundances of metal poor carbon rich lead star: CS29497-030 Authors: Sivarani, T.; Bonifacio, P.; Molaro, P.; Cayrel, R.; Spite, M.; Spite, F.; Plez, B.; Andersen, J.; Barbuy, B.; Beers, T. C.; Depagne, E.; Hill, V.; Francois, P.; Nordstrom, B.; Primas, F. Bibcode: 2002astro.ph.12406S Altcode: We present here the abundance analysis of a metal poor carbon rich lead star, CS29497-030. High resolution and high signal to noise spectra were obtained using the UVES spectrograph on the 8.2m VLT-Kueyen telescope. The observations were made as a part of the Large Programme 165.N-0276, P.I. R. Cayrel. Abundance analysis was done using the latest version of the MARCS model atmospheres (Plez et. al. 1992) and the turbospectrum spectrum synthesis code. We have derived Teff = 6650K from the FeI lines. Visible and infrared broad band colours using the Alonso et al. (1996) calibration, gives similar temperatures. A log g value of 3.5 was obtained from the ionisation equilibrium of FeI and FeII, we remark that this gravity also satisfies the MgI/MgII, TiI/TiII and MnI/MnII equilibria, within errors. The abundance analysis indicates a metallicity, [Fe/H] = --2.7. A large overabundance of carbon ([C/Fe]=2.7) was found. We have also found large enhancement in the s-process elements and in particular lead shows an extremely high abundance of [Pb/Fe]=3.5, which makes this the star with the highest Pb/Fe ratio, up to date. The Pb/Ba ratio is found to be high ([Pb/Ba]=1.2) and the same s true for other second-peak s-process elements(e.g La, Ce, Nd). The star is a known spectroscopic binary with a period of 346 days (Preston & Sneden 2000). The abundance pattern suggests that CS 29497-30 has accreted matter from its companion, when it was in the AGB phase. Title: The Old Star CS 31082-001, the Age of the Universe, and the Nature of the r-process Authors: Cayrel, Roger Bibcode: 2002hst..prop.9359C Altcode: 2002hst..prop.5712C We propose to observe the newly discovered r-process-element enhanced star, CS 31082-001 {Fe/H -2.9}, in order to determine abundances of the heaviest stable elements, using absorption lines that are only reachable in the near UV. This star is the only halo star for which a uranium detection has been reported, and for which the U/Th chronometer has been used to specify an age limit. In order to improve the accuracy of the age determination from U/Th we require abundance estimates of the daughter nuclides -Pb & Bi- for which only upper limits have been obtained from ground-based observations. Such estimates will provide crucial constraints on the initial production ratio of U/Th, resulting in a more strict lower limit on the age of this star's progenitor, hence on the age of the Universe. Measurements of 3rd-peak neutron-capture elements, such as Pt, Os, Ir, and Au, all with lines in the 2400-3100 Angstrom range, will expand our knowledge of element synthesis in the early Galaxy. Our recent ESO-VLT data indicate that the neutron-capture elements in this star exhibit different enhancements as compared with the previously known `` r-process star'' CS 22892-052, an apparent anomaly that must be resolved. CS 31082-001 is the ideal HST target in its class - it is 4-times brighter than CS 22892-052, and less affected by molecular line blending. Consequently, these HST data will become the reference in all future studies of similar stars. Title: First Stars. II. Elemental abundances in the extremely metal-poor star CS 22949--037. A diagnostic of early massive supernovae Authors: Depagne, E.; Hill, V.; Spite, M.; Spite, F.; Plez, B.; Beers, T. C.; Barbuy, B.; Cayrel, R.; Andersen, J.; Bonifacio, P.; François, P.; Nordström, B.; Primas, F. Bibcode: 2002A&A...390..187D Altcode: 2002astro.ph..5232D CS 22949-037 is one of the most metal-poor giants known ([Fe/H]~-4.0), and it exhibits large overabundances of carbon and nitrogen (Norris et al.). Using VLT-UVES spectra of unprecedented quality, regarding resolution and S/N ratio, covering a wide wavelength range (from lambda = 350 to 900 nm), we have determined abundances for 21 elements in this star over a wide range of atomic mass. The major new discovery is an exceptionally large oxygen enhancement, [O/Fe] = 1.97+/-0.1, as measured from the [O I] line at 630.0 nm. We find an enhancement of [N/Fe] of 2.56+/- 0.2, and a milder one of [C/Fe] = 1.17+/-0.1, similar to those already reported in the literature. This implies Zstar =0.01 Zsun. We also find carbon isotopic ratios 12C/13C =4+/-2.0 and 13C/14N =0.03 +0.035-0.015, close to the equilibrium value of the CN cycle. Lithium is not detected. Na is strongly enhanced ([Na/Fe] = +2.1 +/- 0.2), while S and K are not detected. The silicon-burning elements Cr and Mn are underabundant, while Co and Zn are overabundant ([Zn/Fe]=+0.7). Zn is measured for the first time in such an extremely metal-poor star. The abundances of the neutron-capture elements Sr, Y, and Ba are strongly decreasing with the atomic number of the element: [Sr/Fe] ~ +0.3, [Y/Fe] ~ -0.1, and [Ba/Fe] ~ -0.6. Among possible progenitors of CS 22949-037, we discuss the pair-instability supernovae. Such very massive objects indeed produce large amounts of oxygen, and have been found to be possible sources of primary nitrogen. However, the predicted odd/even effect is too large, and the predicted Zn abundance much too low. Other scenarios are also discussed. In particular, the yields of a recent model (Z35Z) from Heger and Woosley are shown to be in fair agreement with the observations. The only discrepant prediction is the very low abundance of nitrogen, possibly curable by taking into account other effects such as rotationally induced mixing. Alternatively, the absence of lithium in our star, and the values of the isotopic ratios 12C/13C and 13C/14N close to the equilibrium value of the CN cycle, suggest that the CNO abundances now observed might have been altered by nuclear processing in the star itself. A 30-40 Msun supernova, with fallback, seems the most likely progenitor for CS 22949-037. Based on observations made with the ESO Very Large Telescope at Paranal Observatory, Chile (programme ID 165.N-0276(A)). Title: The "First Stars" project - preliminary results for the giant stars Authors: Spite, M.; Cayrel, R.; Depagne, E.; Hill, V.; François, P.; Plez, B.; Spite, F. Bibcode: 2002sf2a.conf..511S Altcode: A general view of the status of the ESO LP "Galaxy Formation, Early Nucleosynthesis, and the First Stars" will be given.A new step has been the obtention of 48 orbits of the HST for studying the lines of the r-process elements only accessible from space. Several giant stars are presenting pattern never observed before, confirming the variability of the yields in the early Galaxy. Title: First stars. I. The extreme r-element rich, iron-poor halo giant CS 31082-001. Implications for the r-process site(s) and radioactive cosmochronology Authors: Hill, V.; Plez, B.; Cayrel, R.; Beers, T. C.; Nordström, B.; Andersen, J.; Spite, M.; Spite, F.; Barbuy, B.; Bonifacio, P.; Depagne, E.; François, P.; Primas, F. Bibcode: 2002A&A...387..560H Altcode: 2002astro.ph..3462H We present a high-resolution (R= 75 000, S/N ~ 500) spectroscopic analysis of the bright (V= 11.7), extreme halo giant CS 31082-001 ([Fe/H] = -2.9), obtained in an ESO-VLT Large Programme dedicated to very metal-poor stars. We find CS 31082-001 to be extremely rich in r-process elements, comparable in this respect only to the similarly metal-poor, but carbon-enriched, giant CS 22892-052. As a result of the extreme overabundance of the heaviest r-process elements, and negligible blending from CH and CN molecular lines, a reliable measurement is obtained of the U II line at 386 nm, for the first time in a halo star, along with numerous lines of Th II, as well as lines of 25 other r-process elements. Abundance estimates for a total of 43 elements (44 counting Hydrogen) are reported in CS 31082-001, almost half of the entire periodic table. The main atmospheric parameters of CS 31082-001 are as follows: Teff = 4825 +/- 50 K, log g= 1.5 +/- 0.3 (cgs), [Fe/H] = -2.9 +/- 0.1 (in LTE), and microturbulence 1.8 +/- 0.2 km s-1. Carbon and nitrogen are not significantly enhanced relative to iron. As usual in giant stars, Li is depleted by dilution (log (Li/H) = 0.85). The alpha -elements show the usual enhancements with respect to iron, with [O/Fe] = 0.6+/- 0.2 (from [O I] 6300 Å), [Mg/Fe] = 0.45 +/- 0.16, [Si/Fe] = 0.24 +/- 0.1, and [Ca/Fe] = 0.41 +/- 0.08, while [Al/Fe] is near -0.5. The r-process elements show unusual patterns: among the lightest elements (Z ~ 40), Sr and Zr follow the Solar r-element distribution, but Ag is down by 0.8 dex. All elements with 56 <= Z <= 72 follow the Solar r-element pattern, reduced by about 1.25 dex. Accordingly, the [r/Fe] enhancement is about +1.7 dex (a factor of 50), very similar to that of CS 22892-052. Pb, in contrast, seems to be below the shifted Solar r-process distribution, possibly indicating an error in the latter, while thorium is more enhanced than the lighter nuclides. In CS 31082-001, log(Th/Eu) is -0.22 +/- 0.07, higher than in the Solar System (-0.46) or in CS 22892-052 (-0.66). If CS 31082-001 and CS 22892-052 have similar ages, as expected for two extreme halo stars, this implies that the production ratios were different by about 0.4 dex for the two objects. Conversely, if the Th/Eu production ratio were universal, an age of 15 Gyr for CS 22892-052 would imply a negative age for CS 31082-001. Thus, while a universal production ratio for the r-process elements seems to hold in the interval 56 <= Z <= 72, it breaks down in the actinide region. When available, the U/Th is thus preferable to Th/Eu for radioactive dating, for two reasons: (i) because of its faster decay rate and smaller sensitivity to observational errors, and (ii) because the inital production ratio of the neighboring nuclides 238U and 232Th is more robustly predicted than the 151Eu/232Th ratio. Our current best estimate for the age of CS 31082-001 is 14.0+/- 2.4 Gyr. However, the computed actinide production ratios should be verified by observations of daughter elements such as Pb and Bi in the same star, which are independent of the subsequent history of star formation and nucelosynthesis in the Galaxy. Based on observations of program 165.N-0276(A) obtained with the Very Large Telescope of the European Southern Observatory at Paranal, Chile. Title: Determination of Fundamental Parameters Authors: Cayrel, R. Bibcode: 2002ASPC..274..133C Altcode: 2002ohds.conf..133C No abstract at ADS Title: Foreword (Organizations and strategies in astronomy III) Authors: Cayrel, Roger Bibcode: 2002ASSL..280D...7C Altcode: No abstract at ADS Title: Spectroscopic influence of temperature inhomogeneities Authors: Cayrel, Roger; Steffen, Matthias Bibcode: 2002HiA....12..423C Altcode: The effect of temperature inhomogeneities on the formation of two oxygen lines and one Fe II line has been investigated based on 2-D radiation hydrodynamics simulations of convection in the atmospheres of metal-poor stars. It was expected that the IR O I triplet lines would be enhanced by the temperature inhomogeneities, more than the forbidden [O I] line or Fe II lines. The actual computations done on two snapshots under the assumption of LTE have not confirmed this expectation, instead suggesting that the main difference between "classical" and "dynamical" atmospheres of metal-poor dwarfs is the significantly cooler mean temperature of the dynamical upper photosphere (τRoss<~0.01). Title: Determination of [O/Fe] in BD +23 3130 from ESO VLT-UVES observations Authors: Cayrel, R.; Andersen, J.; Barbuy, B.; Beers, T. C.; Bonifacio, P.; François, P.; Hill, V.; Molaro, P.; Nordström, B.; Plez, B.; Primas, F.; Spite, F.; Spite, M. Bibcode: 2001NewAR..45..533C Altcode: We report a new determination of [O/Fe], the relative logarithmic abundance of O/Fe with respect to the Sun, for the very metal-poor star BD+23 3130 ([Fe/H]=-2.6). The value was derived from the forbidden line [O I] at 630 nm and from six weak Fe II lines, with a S/N ratio substantially larger than those obtained before, thanks to the efficiency of the VLT-UVES instrument at Paranal. We obtain [O/Fe]=0.71±0.25, a value 0.36 dex higher than the value obtained from the same lines by Fulbright and Kraft [AJ 118 (1999) 527], but 0.46 lower than the one derived by Israelian et al. [ApJ 507 (1998) 805] from the UV OH bands. Title: R-process pattern in the Very-Metal-Poor Halo Star CS 31082-001 Authors: Hill, Vanessa; Plez, Bertrand; Cayrel, Roger; Beers, Timothy C. Bibcode: 2001sf2a.conf..205H Altcode: CS 31082-001 was discovered to be very strongly r-process-enhanced, leading to the first 238 abundance measurement in an old star (Cayrel et al. 2001). Together with the observed 232 abundance, this observation provides the opportunity to use both radioactive species for dating the progenitor to this star. However, age computations all rely on the hypothesis that the r-process pattern in this star is solar (as was indeed observed in the other famous r-process enhanced very metal poor star CS22892-052). This hypothesis is tested here by presenting the preliminary analysis of over 20 abundances of neutron-capture elements in the range Z=38 to Z=82. Title: First measurement of the uranium/thorium ratio in a very old star: implications for the age of the Galaxy Authors: Cayrel, Roger Bibcode: 2001sf2a.conf..173C Altcode: In the frame of an ESO Large Programme devoted to the study of the most primitive stars in our Galaxy ([Fe/H] < -2.8) we have been able to measure for the first time the abundance of uranium in a star. Now, the couple U/Th seems the best radioactive chronometer for dating the oldest stars of the Galaxy. Title: Measurement of stellar age from uranium decay Authors: Cayrel, R.; Hill, V.; Beers, T. C.; Barbuy, B.; Spite, M.; Spite, F.; Plez, B.; Andersen, J.; Bonifacio, P.; François, P.; Molaro, P.; Nordström, B.; Primas, F. Bibcode: 2001Natur.409..691C Altcode: 2001astro.ph..4357C The ages of the oldest stars in the Galaxy indicate when star formation began, and provide a minimum age for the Universe. Radioactive dating of meteoritic material and stars relies on comparing the present abundance ratios of radioactive and stable nuclear species to the theoretically predicted ratios of their production. The radioisotope 232Th (half-life 14Gyr) has been used to date Galactic stars, but it decays by only a factor of two over the lifetime of the Universe. 238U (half-life 4.5Gyr) is in principle a more precise age indicator, but even its strongest spectral line, from singly ionized uranium at a wavelength of 385.957nm, has previously not been detected in stars. Here we report a measurement of this line in the very metal-poor star CS31082-0018, a star which is strongly overabundant in its heavy elements. The derived uranium abundance, log(U/H) = -13.7 +/- 0.14 +/- 0.12 yields an age of 12.5 +/- 3Gyr, though this is still model dependent. The observation of this cosmochronometer gives the most direct age determination of the Galaxy. Also, with improved theoretical and laboratory data, it will provide a highly precise lower limit to the age of the Universe. Title: First Measurement of the Uranium/Thorium Ratio in a Very Old Star: Implications for the Age of the Galaxy Authors: Cayrel, R.; Spite, M.; Spite, F.; Hill, V.; Primas, F.; François, P.; Beers, T. C.; Plez, B.; Barbuy, B.; Andersen, J.; Nordström, B.; Molaro, P.; Bonifacio, P. Bibcode: 2001ASPC..245..244C Altcode: 2001aats.conf..244C; 2001astro.ph..4448C During an ESO-VLT large program devoted to high-resolution spectroscopy of extremely metal-poor stars selected from the H&K survey of Beers and colleagues, a [Fe/H] giant star was found to be as enriched in neutron-capture r-process elements as CS 22892-052, but with a much reduced masking by molecular lines. This allowed the detection and the measurement of the uranium line at 3859 A, for the first time in an extremely old star. Making use of the short 238U decay time (4.47 Gyr) we obtained a radioactive dating of the formation of U and Th in of this star, born in the early days of the Galaxy. Title: R-Process Pattern in the Very-Metal-Poor Halo Star CS 31802-001 Authors: Hill, Vanessa; Plez, Bertrand; Cayrel, Roger; Beers, Timothy C. Bibcode: 2001ASPC..245..316H Altcode: 2001aats.conf..316H; 2001astro.ph..4172H The very-metal-poor halo star CS31082-001 was discovered to be very strongly r-process-enhanced during the course of a VLT+UVES high-resolution follow-up of metal-poor stars identified in the HK survey of Beers and colleagues. Both the strong n-capture element enhancement and the low carbon and nitrogen content of the star (reducing the CN molecular band contamination) led to the first $^{238}$U abundance measurement in a stellar spectrum (Cayrel et al. 2001), and the opportunity to use both radioactive species $^{238}$U and $^{232}$Th for dating the progenitor to this star. However, age computations all rely on the hypothesis that the r-process pattern is solar, as this was indeed observed in the other famous r-process-enhanced very metal poor stars CS22892-052 (Sneden et al. 1996, 2000) and in HD115444 (Westin et al. 2000). Here, we investigate whether this hypothesis is verified also for CS31082-001, using a preliminary analysis of over 20 abundances of n-capture elements in the range Z=38 to Z=92. Title: Li/h Measurements in Stars Authors: Cayrel, R.; Spite, F.; Spite, M. Bibcode: 2001coev.conf...85C Altcode: The abundance of Li in stars is still the object of intense activity. New results are available on several type of stars. Abundances have been measured in many extremely young or even pre-main sequence stars, and these data rule out important pre-main sequence depletion of 7Li. The status of Li-rich giants and AGB or post AGB stars has been somewhat clarified, but the discovery of an extremely lithiumrich bright red giant in M3 located in the HR diagram among other lithium normal giants remains a challenge. Finally the case of metal-poor stars has been actively further investigated. A significant amount of 6Li is now measured in 6 stars, and there is now general agreement on a very low level of scatter of Li abundance on the Spite plateau. The connection between the measured abundance of 7Li on the Spite plateau and its cosmological abundance remains a subject of intensive research. An upper limit of the depletion of 7Li of the order of 0.3 dex is suggested by the amount of 6Li present in the post-turnoff very metal-poor halo stars. Title: Element abundance ratios in an extremely metal-poor binary star: CS 22873-139 Authors: Spite, M.; Depagne, E.; Nordström, B.; Hill, V.; Cayrel, R.; Spite, F.; Beers, T. C. Bibcode: 2000A&A...360.1077S Altcode: High-resolution spectra of the extremely metal-poor double-lined spectroscopic binary star BPS CS 22873-139 have been analyzed to determine the metallicity and abundance ratios for a number of elements. From the analysis of the collected radial velocities, new orbital elements are derived as well as an improved mass ratio. In spite of its extreme metal deficiency, [Fe/H]= -3.4, the abundance ratios of CS 22873-139 are not similar to those of a typical Population II star. In particular, the α-elements are not enhanced relative to iron, and the strontium abundance is very low. The abundance pattern of CS 22873-139 is compared to the patterns exhibited by other metal-poor stars which exhibit also very low strontium abundances. There is a large spread of elemental abundance ratios among these stars, suggesting that low strontium abundance may be associated with a variety of nucleosynthesis histories. The abundance ratios of CS 22873-139 are, surprisingly, very similar to those found in a common proper-motion pair HD 134439, HD 134440, even though the metallicity of this system is almost two dex higher, [Fe/H] = -1.7. The ratios are compared to those of another very metal-poor binary star BPS CS 22876-032. The unusual abundance pattern of CS 22873-139 is discussed (by comparison to the predicted yields of zero-metal SN II and hypernovae). The lithium doublet at 6707 Å is not detected in CS 22873-139, but an abundance of lithium consistent with the Spite plateau cannot be excluded, based on the present data. Based on observations made at the European Southern Observatory, La Silla, Chile Title: CHCN Very Metal-Poor Stars: Are These the Missing Pop III ? Authors: Hill, Vanessa; Barbuy, Beatriz; Spite, François; Spite, Monique; Cayrel, Roger; Nordström, Birgitta; Beers, Timothy C. Bibcode: 2000fist.conf...62H Altcode: We have carried out a new analysis of two of the most extreme CH/CN very metal poor giants (originally discovered as part of the ongoing Beers Preston & Shectman HK survey [2]) with high resolution spectroscopy to determine the precise chemical composition of these objects, paying special attention to the heavy s and r neutron-capture elements. The results of this study are presented and discussed in terms of the possible origins for these objects: mass-transfer from a binary companion or intrinsic evolutionary stage of evolved Pop III stars? Title: The (log Teff, Mbol diagram of metal-poor stars with Hipparcos parallaxes : comparison with theoretical isochromes using NLTE iron abundances Authors: Cayrel, R.; Perrin, M. -N.; Lebreton, Y.; Baglin, A.; Fernandes, J. Bibcode: 2000LIACo..35..459C Altcode: 2000ghgc.conf..459C No abstract at ADS Title: Effects of Photospheric Temperature Inhomogeneities on Lithium abundance Determinations (2D) (Invited Paper) Authors: Cayrel, R.; Steffen, M. Bibcode: 2000IAUS..198..437C Altcode: 2000astro.ph..3075C Based on detailed 2D radiation hydrodynamics (RHD) simulations, we have investigated the effects of photospheric temperature inhomogeneities induced by convection on spectroscopic determinations of the lithium abundance. Computations have been performed both for the solar case and for a metal-poor dwarf. NLTE effects are taken into account, using a five-level atomic model for LiI. Comparisons are presented with traditional 1D models having the same effective temperature and gravity. The net result is that, while LTE results differ dramatically between 1D and 2D models, especially in the metal-poor case, this does not remain true when NLTE effects are included: 1D/2D differences in the inferred NLTE Li abundance are always well below 0.1 dex. The present computations still assume LTE in the continuum. New computations removing this assumption are planned for the near future. Title: Lithium Depletion in a [Fe/H]= -3.4 star? Authors: Spite, M.; Spite, F.; Cayrel, R.; Hill, V.; Depagne, E.; Nordström, B.; Beers, T. C. Bibcode: 2000IAUS..198..356S Altcode: No abstract at ADS Title: Les premieres etoiles. Authors: Cayrel, R. Bibcode: 2000CR4.....1..363C Altcode: No abstract at ADS Title: Influence of temperature inhomogeneities on oxygen abundance determination Authors: Cayrel, R.; et al. Bibcode: 2000IAUJD...8E...4C Altcode: The influence of temperature inhomogeneities on abundances derived from the [O I] line and from the O I IR triplet lines will be studied with the help of 2-D hydrodynamical models computed at the Astrophysical Institute of Potsdam by M. Steffen and collaborators. Title: Preliminary Abundance Ratios in an Extremely Metal Poor Binary Star Authors: Nordström, Birgitta; Depagne, Eric; Spite, Monique; Spite, François; Hill, Vanessa; Cayrel, Roger; Beers, Timothy C. Bibcode: 2000fist.conf...64N Altcode: The orbital elements of CS 22873-139 have been revisited and preliminary abundance ratios in this extremely metal poor binary star with [Fe/H] ≈ -3.6 are given. Title: Heavy-element abundances in the CH/CN-strong very metal-poor stars CS 22948-27 and CS 29497-34 Authors: Hill, V.; Barbuy, B.; Spite, M.; Spite, F.; Cayrel, R.; Plez, B.; Beers, T. C.; Nordström, B.; Nissen, P. E. Bibcode: 2000A&A...353..557H Altcode: We have carried out a new analysis of the very metal-poor CH/CN strong stars CS 22948-27 and CS 29497-34. In particular, the effective temperatures were recomputed by comparing newly obtained photometric data to colours derived from model atmospheres computed especially for these stars. Metallicities of [Fe/H] = -2.45 and -2.90 are found, respectively, for CS 22948-27 and CS 29497-34. The abundances of heavy elements have been derived from newly obtained high-resolution spectroscopy in the blue spectral region, together with previously obtained spectra in the red, resulting in a total wavelength coverage of lambda lambda 4000-8200 Ä. We find that the abundance patterns of our stars reflect enrichment by the r-process (as indicated by a high Eu abundance), as well as by the s-process, which could be due to a mass transfer episode from a companion crossing the AGB phase, although no clear evidence for binarity is indicated in the spectra obtained to date. Observations collected at the European Southern Observatory (ESO), La Silla, Chile. Title: The HIPPARCOS HR diagram of nearby stars in the metallicity range: -1.0 < [Fe/H] < 0.3. A new constraint on the theory of stellar interiors and model atmospheres Authors: Lebreton, Y.; Perrin, M. -N.; Cayrel, R.; Baglin, A.; Fernandes, J. Bibcode: 1999A&A...350..587L Altcode: 1999astro.ph..8277L The Hipparcos mission has provided very high quality parallaxes of a sample of a hundred nearby disk stars, of spectral types F to K. In parallel, bolometric fluxes, effective temperatures, and accurate Fe/H ratios of many of these stars became available through infrared photometry and detailed spectroscopic analyses. These new accurate data allow to build the Hertzsprung-Russell diagram of stars of the solar neighbourhood with the smallest error bars ever obtained. We analyse these observations by means of theoretical stellar models, computed with the most recent input physics. We first examine the positions of the objects versus standard theoretical isochrones, corresponding to their chemical composition and age. For these isochrones we have first assumed that the helium content was varying in locksteps with metallicity. The comparison becomes age-independent in the lower part of the HR diagram, where evolutionary effects are negligible. We show that for the unevolved stars, the agreement between real stars and models is fairly satisfactory for stars with metallicity within +/- 0.3 dex of the solar metallicity, but that a conflict exists for stars with metallicity less than [Fe/H] = -0.5. This conflict cannot be resolved by decreasing the helium abundance: values of this abundance below the primordial abundance would be required. On the basis of recent works, we show that the addition of two processes not included in standard models can help solving the above discrepancy. These are (i) correcting the LTE iron abundances using a non-LTE approach and (ii) including microscopic diffusion of He and heavier elements in the stellar interior. The case of the binary star mu Cas is particularly useful to support this conclusion as its mass is also known from its orbit. After inclusion of the two effects, mu Cas A falls on its expected isochrone, within the error bars corresponding to its mass. All stars with -0.3 < [Fe/H] < 0.3 are located between the helium-scaled isochrones corresponding to these metallicities. However five of them are not located exactly where they are expected to be for their metallicity. This may reflect a helium content lower than the metallicity-scaled value. But not necessarily, as a possible sedimentation of the elements might complicate the determination of the helium content. The age of main sequence solar composition stars covers a large range, and the effects of sedimentation are time dependent. Title: Abundances in Very Metal-Poor Stars Authors: Spite, M.; Spite, F.; Cayrel, R.; Hill, V.; Nordström, B.; Barbuy, B.; Beers, T.; Nissen, P. E. Bibcode: 1999Ap&SS.265..141S Altcode: No abstract at ADS Title: In Situ Study of the Thick Disk. Preliminary Results Authors: Katz, D.; Cayrel, R.; Coupry, M. -F.; Perrin, M. -N.; van't Veer, C.; Soubiran, C.; Barbuy, B.; Bienaymé, O.; Friel, E. Bibcode: 1999Ap&SS.265..221K Altcode: We report the advancement of our chemical and kinematical study of thethick disk. The methods used to derive the stellar parameters arediscussed and the preliminary results presented. Title: Lithium-6: evolution from Big Bang to present Authors: Vangioni-Flam, Elisabeth; Cassé, Michel; Cayrel, Roger; Audouze, Jean; Spite, Monique; Spite, François Bibcode: 1999NewA....4..245V Altcode: 1998astro.ph.11327V The primordial abundances of deuterium, 4He, and 7Li are crucial to the determination of the baryon density of the Universe in the framework of standard Big Bang nucleosynthesis (BBN). 6Li is only produced in tiny quantities and it is generally not considered to be a cosmological probe. However, recent major observational advances have produced an estimate of the 6Li/ 7Li ratio in a few very old stars in the galactic halo which impacts the question whether or not the lithium isotopes are depleted in the outer layers of halo stars, through proton induced reactions at the base of (or below) the convective zone. Here, we use (i) an empirical relation, independent of any evolutionary model, to set an upper limit on the 6Li rise compatible with the very existence of the Spite's plateau (i.e. the flat lithium abundance measured in very old stars of the halo of our Galaxy of different iron content) and (ii) a well founded evolutionary model of light elements based on spallation production ( Vangioni-Flam et al., 1997; Vangioni-Flam et al., 1998). Indeed, 6Li is a pure product of spallation through the major production reactions, fast oxygen and alphas interacting on interstellar H, He (especially in the early Galaxy). The rapid nuclei are both synthesized and accelerated by SN II. In this context, the 6Li evolution should go in step with that of beryllium and boron, recently observed by the Keck and HST telescopes. 6Li adds a new constraint on the early spallation in the Galaxy. In particular, if confirmed, the 6Li/ 9Be ratio observed in two halo stars (HD 84937, BD +26°3578 = HD 338529) gives strong boundary conditions on the composition and the spectrum of the rapid particles involved. Both methods converge to show that 6Li is essentially intact in halo stars, and a fortiori 7Li, which is more tightly bound. Moreover, extrapolating empirical and theoretical evolutionary curves to the very low metallicities, we can define a range of the 6Li abundance in the very early Galaxy consistent with Big Bang nucleosynthesis (5.6×10 -14 to 3×10 -13). Following the evolution at increasing metallicity, we explain the abundance in the solar system within a factor of about 2. The whole evolution from Big Bang to present is reasonably reproduced, which demonstrates the general consistency of the present analysis of 6Li. The baryonic density derived from both lithium isotopes is between 1.5 to 3.5% of the critical one, in good agreement with the determination based on independent analyses. Consequently, thanks to these new data and theoretical developments, we show that 6Li can be used to establish stellar 7Li abundances as a valid tracer due to the fact that it allows to reinforce the Spite's plateau as a primordial test of BBN; on the other hand, its early evolution can be used to corroborate the calculated BBN abundances. In the framework of this work, a pregalactic α+ α process producing 6Li is not necessary. Finally, thanks to 6Li, the physics of spallative production of light elements should be more easily mastered when more data will become available. Title: A Grid of Metal-Poor Model Stellar Atmospheres for Stars Born in the Early Galaxy Authors: van't Veer-Menneret, C.; Katz, D.; Cayrel, R.; Soubiran, C. Bibcode: 1999Ap&SS.265..257V Altcode: No abstract at ADS Title: Survival of 6Li, and 7Li, in Metal-Poor Stars Authors: Cayrel, R.; Lebreton, Y.; Morel, P. Bibcode: 1999Ap&SS.265...87C Altcode: 1999astro.ph..2068C The relationship between the depletions of 6Li and 7Li is studied for two models of lithium burning, below the convective zone. The parametersof the depletion models are submitted to the constraint that the slope ofthe 7Li theoretical depletion curve agrees with the slope of theobserved depletion curve, for cool subdwarfs. Other less restrictive modelsare also considered.In all cases, a 6Li depletion less than 0.5 dex implies a 7Lidepletion less than 0.1 dex. With the constraint on the slope of the7Li curve, the depletion of 7Li for the same depletion of 6Li is below 0.05 dex. Title: New high S/N observations of the (6Li) /(7) Li blend in HD 84937 and two other metal-poor stars Authors: Cayrel, R.; Spite, M.; Spite, F.; Vangioni-Flam, E.; Cassé, M.; Audouze, J. Bibcode: 1999A&A...343..923C Altcode: 1999astro.ph..1205C High signal to noise ratio spectra have been obtained with the GECKO spectrograph at CFHT, at a spectral resolution of 100 000, for three metal-poor stars in order to obtain more accurate abundances of the very fragile element (6) Li. For two newly observed stars, BD +42 2667 and BD +36 2165 it appears that the first may have a detectable amount of (6) Li, whereas no (6) Li is found in the second one. The S/N ratio of only a few hundreds obtained for these two faint stars preclude however a firm conclusion. For the third star, the well known object HD84937, a very high S/N of 650 per pixel (over 1000 per resolved spectral element) was obtained, yielding greatly improved accuracy over previous determinations. A value of (6) Li / (7) Li = 0.052 +/- 0.019 (one sigma) is obtained. We also conclude that the no- (6) Li assumption is ruled out at the 95 per cent level, even in the most permissive case, when a variation of all the other free parameters (wavelength zero-point, continuum location, macroturbulent broadening, abundance of (7) Li) is allowed. The possibility that the (6) Li feature is an artifact due to a once suspected binarity of HD 84937 is discussed, with the conclusion that this assumption is ruled out by the extant data on the radial velocity of the object. The (6) Li abundance is compared with recent models of formation of the light elements Li, Be and B. This comparison shows that (6) Li is either undepleted, or only moderately depleted in HD 84937, from its initial value. Under the assumption that the atmospheric depletion of (6) Li and (7) Li in stars is by slow mixing with hot layers (underneath the convective zone), in which these elements can burn, we conclude that the depletion of (7) Li by this mechanism in HD 84937 is less than 0.1 dex. This new upper limit to the efficiency of the depletion of (7) Li by slow mixing burning, in a star located on the Spite plateau, leads to a more secure estimation of the primordial abundance of (7) Li. However, the effect of temperature inhomogeneities in the convective zone, on the derived abundance of lithium still remains to be accurately determined. Based on observations made at the Canada-France-Hawaii Telescope and at Observatoire de Haute Provence Title: Concluding Remarks: Observations Authors: Cayrel, R. Bibcode: 1999ASPC..171..261C Altcode: 1999lcrr.conf..261C No abstract at ADS Title: Calibration of Photometric Absolute Magnitudes for Subdwarfs with Hipparcos Authors: Meillon, L.; Crifo, F.; Cayrel, R.; Perrin, M. -N.; Gómez, A. E. Bibcode: 1999ASPC..167..284M Altcode: 1999hcds.conf..284M In order to obtain better photometric distances for high-velocity stars in the Carney et al. (1994) sample, we have undertaken a calibration of photometric absolute magnitudes. From the intersection between this sample and the Hipparcos catalogue (770 common stars), we keep only single stars with the most reliable parallaxes (σπ/π)HIP <= 0.15). Metallicities, colours and absolute magnitudes of these stars are used with VandenBerg et al. (1998) isochrones in a colour-magnitude diagram. This set of isochrones allows us to derive photometric absolute magnitudes for the highest velocity stars. This photometric parallax calibration is discussed. Title: New Grids of Synthetic Spectra for Abundance Derivation and Population Synthesis Authors: Barbuy, B.; Perrin, M. -N.; Cayrel, R.; Katz, D.; van't Veer, C.; Schiavon, R. P. Bibcode: 1999IAUS..192..365B Altcode: We have built a new grid of synthetic spectra in the wavelength range lambdalambda 4600-5600 Angstroms for [alpha-elements/Fe] = 0.0 and +0.4. This grid is used in combination with an observed spectra library of reference stars in order to derive stellar parameters from low to medium resolution spectra of faint stars. The basis of the method was described in Cayrel et al. (1991, A&A 247, 108) and Meliani et al. (1995, A&A, 300, 349). For the calculation of this new grid already available, the set of atomic and molecular constants were revised and model atmospheres with overshooting parameter appropriate to reproduce the Hβ line wings (suitable to indicate temperatures) were employed. The method is applied to Galactic halo faint stars, bulge stars and Magellanic Cloud stars. It would be suitable also to analyse stars in other nearby galaxies. A computation of a high-resolution grid of spectra in the range lambdalambda 3800-7000 Angstroms, to be used in the context of echelle spectrographs (and also at low resolution), as well as a full grid in the range lambdalambda 3800-10200 Angstroms, to be further used in conjunction with evolutionary population synthesis models are also underway. Title: A Grid of Metal-Poor Model Stellar Atmospheres for Stars Born in the Early Galaxy Authors: van't Veer-Menneret, C.; Katz, D.; Cayrel, R.; Soubiran, C. Bibcode: 1999gecd.conf..257V Altcode: We give a brief description of the automation, on UNIX stations, of the exploitation of the KURUCZ' codes for stellar atmosphere computations, allowing to get rapidly, in a serial mode, grids of models and of corresponding fluxes, Balmer lines profiles(BLP), spectra and Bolometric Correction for the Hipparcos bande Hp(BCHp). We will expose the methods used to get reliable fundamental stellar atmospheric parameters using high resolution and high S/N spectra. We will stress the use of BLP properties to be pure effective temperature criteria while being atmosphere structure indicators. Confrontation and discussion will follow upon the results obtained for some stars of the galactic halo and thick disk. Title: Abundances in Very Metal-Poor Stars Authors: Spite, M.; Spite, F.; Cayrel, R.; Hill, V.; Nordström, B.; Barbuy, B.; Beers, T.; Nissen, P. E. Bibcode: 1999gecd.conf..141S Altcode: No abstract at ADS Title: Survival of 6Li, and 7Li, in Metal-Poor Stars Authors: Cayrel, R.; Lebreton, Y.; Morel, P. Bibcode: 1999gecd.conf...87C Altcode: The most robust fossil-elements from the Big Bang are 4He and 7Li. The early abundance of 4He is mostly determined from extragalactic sources, whereas the early abundance of 7Li is determined from halo stars. The question of knowing if this abundance has been altered or not by nuclear burning in the star itself has been controversial for many years now. New determinations of 6Li in a small number of halo stars permit to discuss this crucial point with stronger constraints. Title: In Situ Study of the Thick Disk. Preliminary Results Authors: Katz, D.; Cayrel, R.; Coupry, M. -F.; Perrin, M. -N.; van't Veer, C.; Soubiran, C.; Barbuy, B.; Bienaymé, O.; Friel, E. Bibcode: 1999gecd.conf..221K Altcode: When people focus on the problem of the formation of the Galaxy, many questions arise. Is the Galaxy born from a single collapsing cloud or from many interacting ones? Did the halo form before the disk or not? Is the thick disk the progenitor of the thin disk? Many models try to answer these questions, playing with the physical processes at the origin of the different structures: free fall, infall, dissipative collapse, secular diffusion of stars, dynamical friction, accretion of galactic fragments, interactions between sub-structures. These formation scenarios are making predictions on the "observables" characterizing the halo, the thick and the thin disk: age, kinematic, abundance of the various elements, density profile. These "observables" are the keys to discriminate between the various models. We have observed a sample of 500 stars in two fields: one in the direction of the north galactic pole (near M3), the other in the direction of the galactic center at b = 47circ (near M5). The sample includes stars with magnitude up to 17, in order to reach distances where each population is dominating (around z = 2 kpc for the thick disk and z = 5 kpc for the halo). All the stars have been studied photometrically, spectroscopically and by the way of proper motion surveys, leading to the knowledge of: effective temperature, surface gravity, metallicity, radial velocity, proper motions, V, B, I magnitudes, distance, U, V, W velocities. This sample of stars will be use to address various questions concerning the thick disk: density profile, scale height, metallicity gradient, kinematic properties, age, continuity with the halo or with the thin disk and we will expose how the data put constraints on the galaxy formation scenarios. Title: On-line determination of stellar atmospheric parameters Teff, log g, [Fe/H] from ELODIE echelle spectra. II. The library of F5 to K7 stars Authors: Soubiran, C.; Katz, D.; Cayrel, R. Bibcode: 1998A&AS..133..221S Altcode: 1998astro.ph..6234S A library of 211 echelle spectra taken with ELODIE at the Observatoire de Haute-Provence is presented. It provides a set of spectroscopic standards covering the full range of gravities and metallicities in the effective temperature interval [4000 K, 6300 K]. The spectra are straightened, wavelength calibrated, cleaned of cosmic ray hits, bad pixels and telluric lines. They cover the spectral range [440 nm, 680 nm] with an instrumental resolution of 42000. For each star, basic data were compiled from the Hipparcos catalogue and the Hipparcos Input Catalogue. Radial velocities with a precision better than 100 m s-1 are given. Atmospheric parameters (Teff, log g, [Fe/H]) from the literature are discussed. Because of scattered determinations in the bibliography, even for the most well-known stars, these parameters were adjusted by an iterative process which takes account of common or different spectral features between the standards, using our homogeneous set of spectra. Revised values of effective temperature, gravity and metallicity are proposed. They are still consistent with the literature, and also lead to the self-consistency of the library, in the sense that similar spectra have similar atmospheric parameters. This adjustment was performed by using step by step a method based on the least square comparison of carefully prepared spectra, which was originally developed for the on-line estimation of the atmospheric parameters of faint field stars (companion paper in the main journal). Based on observations made on the 193 cm telescope at Observatoire de Haute-Provence, France. The library of spectra and corresponding data are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or via http://cdsweb.u-strasbg.fr/Abstract.html Title: On-line determination of stellar atmospheric parameters T_eff, log g, [Fe/H] from ELODIE echelle spectra. I. The method Authors: Katz, D.; Soubiran, C.; Cayrel, R.; Adda, M.; Cautain, R. Bibcode: 1998A&A...338..151K Altcode: 1998astro.ph..6232K We present a method estimating the atmospheric parameters Teff, log g, [Fe/H] for stars observed, even at low signal to noise ratio, with the echelle spectrograph ELODIE on the 193cm telescope at Observatoire de Haute-Provence. The method relies on the least-square comparison of the spectrum of a target star to a library of 211 spectra of reference stars for which the atmospheric parameters are well known and which were observed with the same instrument. In order to obtain a meaningful comparison between target and reference spectra, all features which are not intrinsic to the objects must be removed. This treatment involves the correction of the blaze efficiency for each order, cosmic rays hits and telluric line removal, convolution of the spectra to a common spectral resolution, wavelength scale and flux level adjustment. The library available at the present time covers the effective temperature range [4000K, 6300K], the metallicity range [-2.9, +0.35] and the gravities of both unevolved and evolved stars existing at these temperatures and metallicities. Tests performed with the actual library allow us to estimate the internal accuracy to be 86 K, 0.28 dex and 0.16 dex for Teff, log g, [Fe/H] for a target star with S/N = 100 and 102 K, 0.29 dex and 0.17 dex at S/N = 10. This accuracy will improve in the future as the number of reference stars in the library will increase. The software (named TGMET) has been installed at Observatoire de Haute-Provence for the on-line analysis of the high-resolution spectra of ELODIE, which was originally conceived for accurate radial velocity measurements. based on observations made on the 193cm telescope at Observatoire de Haute-Provence, France Title: VizieR Online Data Catalog: Library of ELODIE spectra (F5-K7 stars) (Soubiran+ 1998) Authors: Soubiran, C.; Katz, D.; Cayrel, R. Bibcode: 1998yCat..41330221S Altcode: A library of 211 echelle spectra taken with ELODIE at the Observatoire de Haute-Provence is proposed. It provides a set of spectroscopic standards covering the full range of gravities and metallicities in the effective temperature interval [4000K, 6300K]. The spectra are straightened, wavelength calibrated, cleaned of cosmic ray hits, bad pixels and telluric lines. They cover the spectral range [440nm, 680nm] with an instrumental resolution of 42000. For each star, basic data were compiled from the Hipparcos catalogue (Cat. <I/239>) and the Hipparcos Input Catalogue (Cat. <I/196>) (Table 1). Radial velocities with a precision better than 100m/s are given. Atmospheric parameters Teff, logg, [Fe/H] from the literature are discussed. Because of scattered determinations in the bibliography, even for the most well-known stars, these parameters were adjusted by an iterative process which takes account of common or different spectral features between the standards, using our homogeneous set of spectra. Revised values of effective temperature, gravity and metallicity are proposed in Table 1. They are still consistent with the literature, and also lead to the self-consistency of the library, in the sense that similar spectra have similar atmospheric parameters. This adjustment was performed by using step by step a method based on the least square comparison of carefully prepared spectra, which was originally developed for the on-line estimation of the atmospheric parameters of faint field stars (Katz et al., 1998A&A...338..151K. Paper I.).

(3 data files). Title: Lithium Abundances in Low-Z Stars Authors: Cayrel, R. Bibcode: 1998SSRv...84..145C Altcode: An historical view of the discovery and subsequent studies of lithium in low-Z stars is presented. The determination of the lithium abundance in extremely low-Z stars, found in the vast Beers, Preston and Shectman survey, is reviewed. The problem of the exact connection between the lithium abundance found in the photospheres of low-Z stars and the true cosmological abundance of lithium is discussed, and identified as the most important problem to be solved in the coming years. Title: Abundances of Metal-Poor Stars and the Formation of the Halo Authors: Cayrel, R. Bibcode: 1998HiA....11...62C Altcode: The origin of the elements in the early Galaxy has been thought to be fairly well understood as primordial matter polluted by ejectae of type II supernovae. Some recent observational results have led to reconsider in more detail this statement. As a result, it is confirmed in some respects, but curiously, when the same metallicity can be found both in the halo and in the thick disk, the stars contaminated by SN Ia ejecta are more the halo stars than the thick disk stars. Title: Lithium Abundances in Low-Z Stars Authors: Cayrel, R. Bibcode: 1998pnge.conf..145C Altcode: No abstract at ADS Title: The Most Metal-Poor Stars Authors: Cayrel, Roger Bibcode: 1998semi.conf..197C Altcode: No abstract at ADS Title: Helium, [Fe/H] Abundances and the HR (log Teff, Mbol) Diagram with HIPPARCOS Data of the Four Nearest Open Clusters: Hyades, Coma Berenices, The Pleiades and Praesepe Authors: Cayrel de Strobel, G.; Cayrel, R.; Lebreton, Y. Bibcode: 1998HiA....11..565C Altcode: No abstract at ADS Title: The HR Diagram for Late-Type Nearby Stars as a Function of Helium and Metallicity Authors: Lebreton, Y.; Perrin, M. -N.; Fernandes, J.; Cayrel, R.; Cayrel de Strobel, G.; Baglin, A. Bibcode: 1997ESASP.402..379L Altcode: 1997hipp.conf..379L Recent theoretical stellar models are used to discuss the helium abundance of a number of low-mass stars for which the position in the Hertzsprung-Russell diagram and the metallicity are known with high accuracy. Hipparcos has provided very high quality parallaxes of a sample of a hundred disk stars, of type F to K, located in the solar neighbourhood. Among these stars we have carefully selected those for which detailed spectroscopic analysis has provided effective temperature and [Fe/H] ratio with a high accuracy. We have calculated evolved stellar models and their associated isochrones in a large range of mass, for several values of the metallicity and of the helium abundance and we took into account an alpha-element enrichment in the metal-deficient stars. The input physics is recent and appropriate to the considered stellar mass range. We discuss the position in the H-R diagram of those stars which can be considered as non-evolved. Once the physics of the models has been fixed, this position only depends on metallicity and helium abundance. We find that the thickness of the observational main sequence is of about 0.25 magnitude, for stars spanning a metallicity range from [Fe/H] = -1 to +0.2, while theoretical stellar models predict a width of about 0.45 magnitude. The position in the H-R diagram of stars of solar metallicity or close to it is well accounted for by theoretical stellar models. Problems arise with the moderately metal deficient stars which lie quite close to the stars of solar metallicity and very far from the theoretical isochrones corresponding to their expected chemical composition. To reconcile theory and observations very low values of the helium abundance, well below the primordial helium abundance, would be needed. We briefly discuss the possible reasons of this discrepancy: improvements to bring to the physics of the models, inaccuracies of observations. Title: The HR Diagram in the Plane log(T_(eff)), M_bol of Pop. II Stars with HIPPARCOS Parallaxes Authors: Cayrel, R.; Lebreton, Y.; Perrin, M. -N.; Turon, C. Bibcode: 1997ESASP.402..219C Altcode: 1997hipp.conf..219C An HR diagram in the plane (log(T_(eff), M_bol) is presented for population II subdwarfs and subgiants having Hipparcos parallaxes known with an accuracy better than 15 per cent. The effective temperatures and the apparent bolometric magnitudes have been taken from measurements made by Alonso et al. (1996), by the IRFM method for the effective temperatures, and direct integration of the fluxes for the bolometric fluxes. This has allowed to bypass the use of bolometric corrections, and the resulting errors. The resulting diagram is interpreted with two sets of isochrones computed with OPAL opacities enhanced in alpha-elements, updated equations of state, a helium abundance close to the primordial value, and a mixing length to pressure scale height ratio calibrated on the Sun. For the first time it has been possible to check the validity of theoretical models for metal-poor stars against accurate observations, and to derive the age of halo stars independently of any globular cluster data. Title: The Bolometric Correction m_(bol) - HP Authors: Cayrel, R.; Castelli, F.; Katz, D.; van't Veer, C.; Gomez, A.; Perrin, M. -N. Bibcode: 1997ESASP.402..433C Altcode: 1997hipp.conf..433C By the use of model atmospheres fluxes computed with Kurucz's ATLAS9 code, we have investigated the behaviour of the computed bolometric correction of the Hipparcos Hp band, namely BCHp=m_bol-Hp, with the basic physical parameters effective temperature, gravity and metallicity. The theoretical relations of BCHp versus effective temperature(T_(eff)) are compared to empirical ones. Title: a Kinematical and Chemical Probe of the Galaxy Authors: Soubiran, C.; Cayrel, R.; Perrin, M. N.; Bienayme, O.; Friel, E.; Coupry, M. F. Bibcode: 1997ASSL..212..219S Altcode: 1997wfs..conf..219S No abstract at ADS Title: Helium, [Fe/H] Abundances and the HR (logTeff, Mbol) Diagram with HIPPARCOS Data of the four Nearest Open Clusters: Ursa Major, Hyades, Coma Berenices and the Pleiades Authors: Cayrel de Strobel, G.; Cayrel, R.; Lebreton, Y. Bibcode: 1997IAUJD..14E..34C Altcode: Here for the first time not only we discuss the metal abundance of F,G, and K stars in the four nearest open clusters, but we give an estimate of the value of their He abundance also. The study of the He abundance is now possible thanks to Hipparcos which has permitted, in improving the values of the individual distances of the cluster stars, to derive the four observational main sequences in the HR (logTeff,Mbol) diagram with god precision.The four main sequences have been interpretd with theoretical internal structure models constituing the ZAMSes. The position of these ZAMSes in the (logTeff,Mbol) diagram depends upon two free parameters only: the He-abundance, Y, and the metal abundance abundance, Z. In comparing the observational main sequences with theoretical ZAMSes and having previously determined the effective temperature and the metallicity of the consituing stars with the help of high resolution, high S/N detailed analyses, it is now possible to determine the only missing parameter of the clusters: their He-abundance. Title: The Most Metal-Poor Stars Authors: Cayrel, Roger Bibcode: 1997seim.proc..197C Altcode: No abstract at ADS Title: Analysis of two CH/CN-strong very metal-poor stars. Authors: Barbuy, B.; Cayrel, R.; Spite, M.; Beers, T. C.; Spite, F.; Nordstroem, B.; Nissen, P. E. Bibcode: 1997A&A...317L..63B Altcode: Two very metal-deficient stars, BPS CS 22948-27 and BPS CS 29497-34, recently identified in the HK objective-prism/interference-filter survey of Beers and collaborators, which exhibit, at low resolution, strong CH and CN bands and metallicities [Fe/H]~-3 , have been observed at high spectral resolution and high S/N at the NTT at ESO with the EMMI echelle spectrograph. A preliminary analysis of these spectra shows that these objects are very unusual. The high-resolution work confirms the very low metallicity of these stars and indicates: (i) effective temperatures T_eff_~4000K and surface gravities logg~0.0 to 1.5; (ii) a very large overabundance of carbon and nitrogen, by ~2dex with respect to iron; (iii) a similar overabundance of a few neutron-capture elements, in particular Ba, La and Nd, also by ~2dex; (iv) a low isotopic ratio ^12^C/^13^C; (v) a variable radial velocity for one of the stars (CS 22948-27). These findings suggest that the two stars are extreme cases of CH stars. The spectra are considerably richer in molecular bands than the spectrum of the remarkable star CS-22892-52, identified in the same survey and studied by Sneden et al.. The determination of the ratio of s-process to r-process elements in these two stars must await observations in the blue spectral region. Title: On the use of CA I triplet lines as luminosity indicators. Authors: Cayrel, R.; Faurobert-Scholl, M.; Feautrier, N.; Spielfieldel, A.; Thevenin, F. Bibcode: 1996A&A...312..549C Altcode: Many strong lines formed in stellar atmospheres are well known to be dominated by pressure broadening, therefore their wings are a precious help for determining the surface gravities of dwarf or subgiant stars. In this paper, we explore the possibility for using the wings of the Ca I triplet lines 6102, 6122, 6162A for which recent theoretical computations of the damping are available. A NLTE code for radiative transfer was used to check these new computations against the integrated Solar Spectrum. We report here that (i) there is a spectacular improvement in the fit of the computed profile with the observed one when the new quantum mechanical computations are used instead of the classical Unsoeld's expression of the Van der Waals damping constant (ii) the departures from LTE in the computation of the wings of these lines are negligible, and this justifies the use of LTE computations for the determination of the surface gravities of G type stars, by this method. Title: The first generations of stars Authors: Cayrel, R. Bibcode: 1996A&ARv...7..217C Altcode: Up to a decade ago, searches for population III stars (i.e. with strictly the chemical composition left by the Big Bang) had led to the results that (1) no such star had been found, (2) stars with metallicities significantly below [Fe/H] = -2.5 were exceedingly rare. Thanks to a major survey, undertaken by Beers, Preston and Shectman 18 years ago, covering about 7500 square degrees in the sky, and down to magnitude B =16.0, the situation has drastically changed. The observational limit towards the lowest metallicities is now about [Fe/H] = -4, i.e. 4 dex below the solar metallicity Zsolar = 0.02, (a level of pollution by supernova ejecta of only a few ppm), and over 100 stars are known with metallicities [Fe/H] in the range -4 to -3. The study of this sample, and of a few stars found more serendipitously, has allowed a number of new conclusions: (i) The cosmological element 7Li stays constant (prolongation of the Spite's plateau) down to the lowest metallicities, a great observational gift to the hot Big Bang cosmology (ii) All heavier elements show a roughly linear increase with the abundance of O (or even Fe if the metallicity is below [Fe/H] = -1), including the other light elements, Be and B. This last point has led to a reappraisal of the current view that they were produced by spallation of interstellar nuclei by galactic cosmic rays, because the rise of those elements with metallicity should then have been more quadratic than linear. An alternative new perspective is that these elements are produced by spallation of the primary nuclei ejected by SNe ii against protons of the interstellar medium. (iii) The ratio of the alpha elements (O, Si, Mg,...) to iron also stays constant down to the lowest metallicities, at about 3 times the solar value. (iv) Significant deviations to a lockstep variation of the various elements within the iron-peak start to appear below [Fe/H] = -2.5. The strongest are a decrease of [Cr/Fe] and an increase of [Co/Fe] when [Fe/H] decreases from -2.5 to -4.0. These trends are not explained by the current status of explosive nucleosynthesis. (v) A great scatter of the abundances of the neutron capture elements relative to iron appears at very low metallicities. Similar scatter is seen for [Al/Fe]. A remarkable star with [Fe/H] = -3.1, CS 22892-052, has been found, with a superb spectrum of the r-elements, involving over-abundances of those with respect to iron by factors ranging between 10 and 50. (vi) The kinematics of the very metal-poor stars is similar to that of other halo stars, with a complete lack of systemic rotation in an inertial frame, if not a small amount of counter-rotation in the Galaxy. Evidence exists that the velocity ellipsoid is radially elongated for stars within 10 kpc from the galactic center, whereas it is more spherical or even radially contracted at 20 kpc from the galactic center. (vii) The low metallicity stars were likely formed at an early cosmological epoch (z > 5 if H0~ 65 km/s), before the Galaxy had developed a disk. The new views concerning the sizes of the Lyα clouds open the possibility that the low-metallicity Lyα systems are large halos having the right metallicity for being protogalaxies, just forming early stellar generations. (viii) One may wonder why, if more than 100 stars are known with metallicities between [Fe/H] = -4 to -3 no pop. III has been found, or even not one star near [Fe/H] = -5. Different kinds of explanations have been proposed, with none conclusive at present. Either we have already observed a pop. III star, but its pristine Big Bang composition has been corrupted by a small amount of interstellar matter accreted during its 10 Gyr of orbiting in an already-enriched gas, or the collective process of star formation has polluted the medium before it has produced the low-mass stars we can still observe now, or, simpler, pop. III stars exist, but are sufficiently rare that we have not yet observed a volume large enough to have found one. Title: HIPPARCOS et les sondages profonds. Authors: Cayrel, R. Bibcode: 1996udh..conf..143C Altcode: Les sondages profonds concernent des objets à des distances trop élevées pour e^tre directement accessibles à HIPPARCOS. Cependant HIPPARCOS permettra de calibrer les distances photométriques pout les objets représentés dans un voisinage solaire étendu, disons jusqu'à 50 parsecs, et d'améliorer ainsi considérablement la détermination des distances des étoiles rencontrées dans les sondages profonds, pénétrant le disque épais in situ et le halo. Title: Contribution to the study of the visual binary ζ Herculis: a detailed analysis of ζ Herculis A. Authors: Chmielewski, Y.; Cayrel de Strobel, G.; Cayrel, R.; Lebreton, Y.; Spite, M. Bibcode: 1995A&A...299..809C Altcode: This research is a contribution to the study of the physical structure and the state of evolution of the binary system ζ Herculis ( ζ Her). This double star has a period of 34.49 years, which is half as short as that of the system of α Centauri. In order to determine with very great precision the fundamental parameters of the atmosphere of the primary component ζ Her A, a new detailed spectroscopic analysis, based on high resolution and high signal/noise spectra, has been carried out for this star. The duplicity of the observed star has been taken into account in as detailed a way as possible. The present analysis attributes to the star a higher effective temperature than that found in previous detailed analyses, and a solar metallicity. The new results are used to rediscuss the age and the masses of the system, with the help of internal structure models. Title: Quelques remarques sur Elodie. Authors: Cayrel, R. Bibcode: 1995LOHP...14....8C Altcode: No abstract at ADS Title: Distribution spatiale, cinématique et métallicité des populations stellaires de la Galaxie. Authors: Soubiran, C.; Cayrel, R. Bibcode: 1995LOHP...14....2S Altcode: No abstract at ADS Title: Stellar population study in the galactic direction (l=~0deg, b=~45deg). Authors: Perrin, M. -N.; Friel, E. D.; Bienayme, O.; Cayrel, R.; Barbuy, B.; Boulon, J. Bibcode: 1995A&A...298..107P Altcode: Quantitative medium resolution spectroscopic observations have been performed on a sample of stars in a field of 9.6 square degrees in the galactic direction (l=~0deg, b=~45deg), for which proper motions and photographic photometry have been recently obtained. Radial velocities, effective temperatures, surface gravities and metallicities have been derived, leading to a complete set of kinematic and astrophysical parameters for 28 stars, with apparent V magnitudes near 14.25 and B-V in the range 0.93-1.03, to allow a safe discrimination between dwarfs and giants from the Mg I green triplet. The main finding of these observations is the very low proportion of population II giants in this direction, about 5 to 10 times less than the predictions of current galactic models. A discussion of this result in connection with similar works available in the literature is presented. Title: Lithium in metal deficient binaries. Authors: Spite, M.; Fleming, T.; Cayrel, R.; Pasquini, L.; Spite, F. Bibcode: 1995MmSAI..66..337S Altcode: No abstract at ADS Title: A New Sample of Thick Disk and Halo Stars Authors: Soubiran, C.; Perrin, M. N.; Cayrel, R.; Chereul, E. Bibcode: 1995IAUS..164..386S Altcode: No abstract at ADS Title: Nucleosynthesis in the First Galactic Stars Authors: Andersen, J.; Nordström, B.; Beers, T. C.; Cayrel, R.; Spite, F.; Spite, M.; Nissen, P. E.; Barbuy, B. Bibcode: 1995svlt.conf...75A Altcode: No abstract at ADS Title: The effective temperature determination Authors: Cayrel, R. Bibcode: 1995HiA....10..395C Altcode: No abstract at ADS Title: Detailed Analysis of Stars in the Galactic Bulge with the VLT Authors: Cayrel, R.; Nissen, P. E. Bibcode: 1995svlt.conf..171C Altcode: No abstract at ADS Title: A case study of the quadruple system ξ Ursae Majoris: its activity and lithium depletion. Authors: Cayrel de Strobel, G.; Cayrel, R.; Friel, E.; Zahn, J. -P.; Bentolila, C. Bibcode: 1994A&A...291..505C Altcode: The quadruple system ξ UMa is an interesting test case for the numerous problems encountered when studying the evolutionary status, chromospheric activity and lithium depletion of solar-type stars. We have carried out a detailed analysis of the major components A and B of ξ UMa from high resolution, high signal-to-noise CFHT spectra. We determine accurate temperatures for each of the principal components, neither disturbed by their invisible, much less massive companion, and find that the two differ in temperature by 300 K, one being somewhat hotter than the Sun, the other cooler. The metal abundances derived from iron and a few other elements are identical for the two stars, and the system is moderately metal-deficient, by a factor of two with respect to the Sun. We concur with previous studies that lithium is fairly abundant in A whereas it is below detection in B: we measured log N(Li)=2.33 in A and place a more stringent upper limit log N(Li)<0.8 for B. We discuss this unusual combination of lithium abundances and the position of the stars in the HR diagram in the light of the complex binary nature of the two components, and of current theories of stellar evolution and of lithium depletion. We suggest that B has kept a high level of activity because its rotation is tidally locked with the orbital motion, and that it has therefore lost about ten times more matter than a single star of the same mass, which explains its strong lithium depletion. Title: Incorporating the atmosphere in stellar structure models: the solar case Authors: Morel, P.; van't Veer, C.; Provost, J.; Berthomieu, G.; Castelli, F.; Cayrel, R.; Goupil, M. J.; Lebreton, Y. Bibcode: 1994A&A...286...91M Altcode: The diffusion limit of the transfer equation used in the calculations of stellar interior models is only valid at large Rosseland optical depth. From atmosphere models obtained with ATLAS 9 (Kurucz), it is shown here that the diffusion limit of the transfer equation becomes valid only at Rosseland optical depths τ_R_ >~ 10 that is at a location well inside the Sun's convective zone. For the calculations of stellar evolution, the atmosphere is built from T(τ) laws that are derived either from theory or from full atmosphere computations; such a T(τ) law depends upon effective temperature and gravity, therefore on the evolutionary state of the model. Hence, in general, when following the evolution of a star, various T(τ) laws need to be introduced. In the case of the Sun, however, we show here that the atmosphere can be restored with the use of only one T(τ) law. Particular efforts have been made to include physics as consistent as possible in both the model atmosphere from which one derives T(τ) laws and the internal structure calculations which use them; as a result, we can rebuild the atmosphere in stellar models with an accuracy of about +/- 0.5% for the sound speed and the pressure. Remaining discrepancies are of small effect on solar calibrated models. For the solar oscillations, such small discrepancies generate frequency differences no larger than 2μHz for low degrees modes to about 10μHz for modes of large degrees around 400. Title: Stellar atmospheric parameters for F-G-K stars from low-resolution data: method and application to a sample of proper motion stars Authors: Cuisinier, F.; Buser, R.; Acker, A.; Cayrel, R.; Jasniewicz, G.; Fresneau, A. Bibcode: 1994A&A...285..943C Altcode: We develop a general method which allows us to derive fundamental stellar parameters (T_eff_, [M/H]) of F, G, and K dwarfs from low-resolution spectra covering the wavelength range 370-780 nm and using three different grids of model atmosphere flux distributions. Two extreme cases are explored: (1) broad-band synthetic color indices, which exploit a large fraction of the available wavelength range, but at highly degraded spectral resolution, and (2) synthetic spectrum fitting, which takes full advantage of the available resolution in the data, but which is limited to a relatively narrow wavelength interval. We show that, while in either case the initial model-derived parameter values differ systematically from published results obtained via high-resolution spectroscopy these spectroscopic data can be used to properly calibrate the models. Thus, as an application, we were able to derive abundances for 40 proper motion stars, selected from Fresneau (1990). Within the systematic biases that could exist, the derived metallicity distribution is bimodal, one mode centered on [M/H] = 0.0dex (thin disk) and the other on [M/H] = -0.6dex (thick disk), biased towards the thick disk. Furthermore, three low metallicity stars and a super metal-rich one have been discovered. Title: Restoration of the atmosphere in solar models Authors: Morel, P.; van't Veer, C.; Berthomieu, G.; Cayrel, R.; Castelli, F.; Goupil, M. J.; Lebreton, Y.; Provost, J. Bibcode: 1993ASPC...40...57M Altcode: 1993IAUCo.137...57M; 1993ist..proc...57M No abstract at ADS Title: The first stars in the Galaxy. Authors: Cayrel, R. Bibcode: 1993oee..conf..465C Altcode: No abstract at ADS Title: Early populations of stars Authors: Cayrel, R. Bibcode: 1993flus.conf..171C Altcode: No abstract at ADS Title: Lithium in Population II Stars Authors: Spite, F.; Spite, M.; Cayrel, R.; Huille, S. Bibcode: 1992IAUS..149..490S Altcode: No abstract at ADS Title: Stellar Parameters in the Basel Field SA 141 Authors: Perrin, M. -N.; Cayrel, R.; Barbuy, B.; Buser, R. Bibcode: 1992IAUS..149Q.513P Altcode: No abstract at ADS Title: From spectrophotometry to fundamental parameters, effective temperature, gravity and metallicity. Authors: Cayrel, R. Bibcode: 1992ctap.conf..655C Altcode: The practical problem of deriving the fundamental parameters, effective temperature, gravity and metallicity from spectrophotometric observations is considered. A methodology is established, and experiments with synthetic spectra are performed. The respective merits of spectroscopy, spectrophotometry and photometry are compared, with and without interstellar reddening. Examples are taken in the field of G stars, for which a full span of metallicity exists in the Galaxy. Title: Trouble in the Magellanic Clouds - First results from the Key Programme on coordinated investigations of selected regions in the Magellanic Clouds Authors: de Boer, K. S.; Spite, F.; Francois, P.; Cayrel, R.; Spite, M.; Baschek, B.; Koeppen, J.; Wolf, B.; Stahl, O.; Juettner, A.; Seggeweiss, W.; Bomans, D. J.; Grebel, E. K.; Geyer, E. H.; Richtler, T.; Vallenari, A.; Koornneef, J.; Israel, F. P.; Molaro, P.; Monai, S.; Vladilo, G.; D'Odorico, S.; Leisy, R.; Dennefeld, M.; Ferlet, R.; Vidal-Madjar, A.; Stasinska, G.; Azzopardi, M.; Meyssonnier, N.; Muratorio, G.; Rebeirot, E.; Lequeux, J. Bibcode: 1991Msngr..66...14D Altcode: 1991Mgr....66...14D Results of coordinated subprojects on selected regions in Magellanic Clouds performed in the framework of the Key Program are briefly reviewed. The subprojects include spectroscopic survey with EFOSC (Marseille, Paris, Uppsala), CCD photometry of small field within the regions (Bonn), IRAC photometry of small fields within the regions (Baltimore, Leiden), stellar spectroscopy for studying element abundances in the hot and cool stars (Heidelberg and Meudon, respectively), the interstellar absorption lines (Trieste, Paris), and the spectra of emission nebulae (Paris). Title: A grid of synthetic spectra for the determination of effective temperature, gravity and metallicity of F,G and K stars. II. Application to 41 stellar spectra taken in the Basel field of SA 141. Authors: Cayrel, R.; Perrin, M. -N.; Buser, R.; Barbuy, B.; Coupry, M. -F. Bibcode: 1991A&A...247..122C Altcode: A grid of synthetic spectra is used to derive the atmospheric parameters temperature Teff, gravity log g and metallicity [M/H], besides the radial velocity, from low-resolution spectra of 41 stars in the Basel field SA 141 in the direction of the south galactic pole (l = 245°.0, b = -85°.8).

The metallicity distribution as a function of distance from the galactic plane is obtained and discussed. Title: A grid of synthetic spectra for the determination of effective temperature, gravity and metallicity of F,G and K stars.I. Description of the method. Authors: Cayrel, R.; Perrin, M. -N.; Barbuy, B.; Buser, R. Bibcode: 1991A&A...247..108C Altcode: The computation of a grid of synthetic spectra in the wavelength region λλ4780-5300 Å is described.

With the use of this grid, a method is developed for deriving the stellar parameters temperature, gravity and metallicity from a low-resolution spectrum.

The use of the grid is tested for 20 reference stars, in two ways. The stellar parameters for these 20 stars are derived (1) directly from the grid, (2) using the synthetic grid in conjunction with the observed spectrum of another reference star.

A best fit is obtained by the second method, i.e., by using the grid in combination with a number of standard stars, in this way establishing corrections to the parameters obtained exclusively from the grid. Title: The earliest observable stellar generation. Authors: Cayrel, R. Bibcode: 1991pgrp.work..155C Altcode: The observation of the oldest stars gives evidence on events which took place at epochs as early as z ≅ 5 to 10. This evidence is summarized and possible interpretations are discussed. One of them is that the old population II is of extragalactic origin and was accreted by the Galaxy when it became an isolated system. Title: The Fm-Am Stars: Observed Anomalies Authors: Cayrel, R.; Burkhart, C.; van't Veer, C. Bibcode: 1991IAUS..145...99C Altcode: No abstract at ADS Title: Derivation of stellar parameters using a grid of synthetic spectra. Authors: Barbuy, B.; Perrin, M. -N.; Cayrel, R. Bibcode: 1990RMxAA..21..406B Altcode: A grid of synthetic spectra is built, for a set of stellar parameters, in the spectral region λλ4780 - 5300 Å. Spectrophotometric indices in this region are chosen and measured in the synthetic spectra; these theoretical indices are directly compared to those measured in the observed spectra, in order to obtain the stellar parameters temperature, gravity and metallicity. Title: The construction of the Canada-France-Hawaii Telescope Authors: Cayrel, R. Bibcode: 1990JRASC..84....3C Altcode: The history of the construction of the Canada-France-Hawaii Telescope (CFHT) between 1974 and 1979 is examined. Consideration is given to the beginnings of the CFHT program, site selection, the administrative aspects of the program, and the roles of the participating countries in the development and construction of the telescope. The configuration of the CFHT is illustrated and the process of reassembling the telescope at Mauna Kea, Hawaii is described. The development of the telescope's mirror, control system, dome, and mechanical structure is reviewed. Title: A review of IMF theories Authors: Cayrel, R. Bibcode: 1990ASSL..162..343C Altcode: 1990ppfs.work..343C An overview is presented of theories of the initial mass function (IMF), starting from those essentially based on stochastic arguments to those involving more physics. Consideration is given to the scheme of Auluck and Kothari (1960, 1965), hierarchical theories, the predicted IMF, coalescence theories, DiFazio's theory (1986), fragmentation from sheets and filaments (bimodal star formation), and the criteria for determining stellar masses. The following concepts are proposed as being the most likely to survive: the general statistical arguments supporting log-normal laws, or power laws; the opacity-limited fragmentation concept; and the concept that the IMF is not a pure product of cloud fragmentation processes but also depends on internal properties of the object itself. Title: A thorough spectroscopic study of the very nearby triple system : 36 Ophiuchi. Authors: Cayrel de Strobel, G.; Perrin, M. N.; Cayrel, R.; Lebreton, Y. Bibcode: 1989A&A...225..369C Altcode: The three K-star components of the 36 Ophiuchi system have been analyzed in detail on high resolution, high S/N ESO Reticon spectra. The atmospheric parameters of the stars (effective temperature, spectroscopic gravity, microturbulence, metal abundances, and degree of chromospheric activity) have been determined. The position of the observational ZAMS built up by the three stars has been compared with theoretical ZAMS. The agreement between the iron abundances is excellent for the three components. A discussion of the masses of the components is also given. Title: Strong lithium in the very nearby K-dwarf HD 17925. Authors: Cayrel de Strobel, G.; Cayrel, R. Bibcode: 1989A&A...218L...9C Altcode: On a Reticon spectrum centered at 6714 A, taken with the 1.4 m coude auxiliary telescope and with the coude echelle spectrograph of ESO, it was found that the cool K2V star, HD 17925 has a very strong lithium line. This strong lithium line in such a cool star (5090 K) indicates that HD 17925 must be very yound. Even in the comparatively young Hyades, lithium is already totally depleted in stars with effective temperatures around 5000 K. It is proposed that the star comes from the Scorpio-Centaurus complex where it was formed only a few million years ago. Title: La vie et l'œuvre de Bengt Strömgren (1908 - 4 July 1987) Authors: Cayrel, R. Bibcode: 1989CRASG...6..609C Altcode: No abstract at ADS Title: Learning about young globular clusters. Authors: Cayrel, R.; Tarrab, I.; Richtler, T. Bibcode: 1988Msngr..54...29C Altcode: 1988Mgr....54...29C Even after many decades of intensive investigation globular clusters still fascinate astronomers. Galactic globular clusters are "fossils" of the epoch of galaxy formation and sampies of a very early, but still reachable stellar generation. The situation is different in the Magellanic Clouds where globular-cluster- like objects with a wide variety of ages can be found. We see globular clusters which, judged by their stellar content, cannot be much older than 107 yr. Their integrated light is dominated by a slightly evolved upper main sequence. Therefore, they have often been referred to as "blue globular clusters". the question why such clusters are found in the Magellanic Clouds (and perhaps in some other galaxies like M33 and NGC 2403) and not in the Milky Way is certainly of significance for the general understanding of galaxy evolution (see lAU Symp. 126 for more information). Title: Observations on cosmic abundances of 4He and 7Li, comparison with primordial nucleosynthesis predictions. Authors: Cayrel, Roger Bibcode: 1988ESASP.283...69C Altcode: 1988ssfp.rept...69C; 1988ssfp.conf...69C Observations of He-4 in metal poor galaxies and of Li-7 in galactic subdwarfs were used to derive constraints on the initial abundances of the elements. An initial abundance of He-4 of 0.23 to 0.24 by mass, and an initial abundance of 10 to the minus 10th power by number of atoms for Li-7, with respect to hydrogen are obtained. These abundances are compatible with a hot big bang having a nucleons/photons ratio of about 2 to 5 times 10 to the minus 10th power, assuming 3 families of particles. Title: Globular clusters and primordial composition. Authors: Cayrel, Roger Bibcode: 1988IAUS..126..431C Altcode: The primordial chemical composition and the abundance of the primordial elements in globular clusters, specifically in population II, are reviewed. Timetables of the big bang and of important events during the nucleosynthesis period are presented, and the predicted primordial abundances in the big bang are examined. The abundances of He-3 and He-4, D, and Li; the metallicity of clusters; and the abundance ratios in globular-cluster stars are discussed. Title: Data Analysis Authors: Cayrel, R. Bibcode: 1988IAUS..132..345C Altcode: The relationship between the r.m.s. photometric accuracy on the data points of a stellar spectrum and the final accuracy on abundances and physical parameters derived from these data is discussed. Title: The Iron Abundances, [Fe/H] in the Four Nearest Open Clusters : Pleiades, Ursa Major Stream, Coma Berenices and Hyades Authors: Cayrel, R.; Cayrel de Strobel, G.; Campbell, B. Bibcode: 1988IAUS..132..449C Altcode: Iron abundances, [Fe/H] have been studied in G and K dwarfs of the four nearest clusters. With the exception of the Pleiades stars which are all fainter than the 10th magnitude, the observational material consists of high resolution, high S/N spectra. The Hyades is the only cluster with a significative overmetallicity with respect to the sun. Title: A new interpretation of the metallicity histogram of globular clusters. Authors: Cayrel, R. Bibcode: 1987JApA....8..153C Altcode: A new interpretation is given to the low metallicity peak of the bimodal metallicity histogram of galactic globular clusters. It is proposed that these globular clusters are primordial, i.e., formed out of big-bang matter. Their nonvanishing metallicity is attributed to pollution by supermassive stars like R 136a. The first stellar generation is formed out of the 'dirty' primordial matter. Title: First results of a spectroscopic search for gravitational mirages. Authors: Reboul, H.; Vanderriest, C.; Fringant, A. M.; Cayrel, R. Bibcode: 1987A&A...177..337R Altcode: The first results of a systematic search for gravitational mirages among close pairs of blue objects are presented and some representative cases are discussed. The spectroscopic study of 15 candidates did not yield new gravitational mirages but revealed about 40 percent of the extragalactic physical systems including a large proportion of quasars, active galaxies, and H II regions. Title: Star formation from primordial matter. Authors: Cayrel, R. Bibcode: 1987SRToh...7..207C Altcode: The gravitational collapse of a primordial cloud does differ of the gravitational collapse of normal interstellar clouds, mostly because radiative cooling processes and opacity are very different. Fragmentation is of course affected by this. In the seventies it was believed that fragmentation could be inhibited below one or several solar masses in a zero-metal environment, leading to a first stellar generation with no low-mass stars. However the problem appears more complex now, and recent work on the subject, both theoretical and observational, are surveyed. Title: Projets scientifiques pour un grand télescope. Authors: Cayrel, R. Bibcode: 1987JAF....29...27C Altcode: No abstract at ADS Title: The early chemical evolution of the halo and population III. Authors: Cayrel, R. Bibcode: 1987ESOC...27..627C Altcode: 1987sedo.work..627C It is noted that there is no clear bottom of metallicity in the Galaxy. Even though a number of stars with metallicities below 0.001 Z-solar have been found, no star with zero metallicity has been found. No unbiased metallicity histogram covering the range 0-0.1 Z-solar exists for the field halo population. It is suggested that the scarcity of very metal-poor stars may be the result of self-pollution in formation regions of stars orginating from the gravitational collapse of primordial clouds. Title: Star formation from primordial matter Authors: Cayrel, Roger Bibcode: 1987cega.proc...41C Altcode: The topic of the star formation from primordial matter is examined theoretically. Consideration is given to the questions of the fragmentation limit in the primordial clouds, the mass-function of fragments as a function of metallicity, the internal structure and evolution of zero-metal stars, and the nucleosynthesis in the primordial galaxy. The conclusions drawn from the theoretical considerations suggest that the formatiom of stars from primordial matter must have occurred, although no direct observational evidence has been jet found. Title: High resolution analysis of a star in the young SMC globular cluster NGC 330. Authors: Spite, M.; Cayrel, R.; François, P.; Richtler, T.; Spite, F. Bibcode: 1986A&A...168..197S Altcode: The analysis of CASPEC spectra of the supergiant star A7 in the young cluster NGC 330 (Small Magellanic Cloud) shows that the star has a metellacity much smaller than the metallicity of the few field supergiants of the SMC which have been analyzed. The metallicity of the star is similar to that found in typical globular clusters of the Galaxy, but does not deviate significantly from that of some H II regions of the SMC. The distribution of the individual abundances of the elements is definitely nonsolar, and is similar to the distribution found in the typical globular clusters of the Galaxy. The abundances of heavy elements (rare earths) and in particular of Europium, is enhanced relative to the typical globular clusters of the Galaxy; such anomaly is known in two halo field giants of the Galaxy, HD 115444 and DH 110184. The resonance line of lithium is observable, and hence the star suffered only a small mass loss. Title: And if population III were population II? Authors: Cayrel, R. Bibcode: 1986A&A...168...81C Altcode: Based on the assumption that the first stellar generation was formed out of massive primordial clouds, it is shown that the mean metallicity of the low-mass stars of the first stellar generation is expected to have a value similar to that of population II. Population II stars are interpreted as former members of large associations of which globular clusters are also remnants. The proposed scenario is consistent with the lack of success of finding metal-free low mass stars, the invariance of the metallicity histogram of the spherically distributed globular clusters with galactocentric distance, the paucity of G dwarfs with intermediate metallicity, and the O/Fe ratio difference in population II and in the disk population. Title: The first stars. Authors: Barbuy, B.; Cayrel, R.; Silk, J. Bibcode: 1986Rech...17.1060B Altcode: No abstract at ADS Title: Steps towards the abundance scale. I. The abundance of heavy elements in the Hyades cluster. Authors: Cayrel, R.; Cayrel de Strobel, G.; Campbell, B. Bibcode: 1985A&A...146..249C Altcode: An analysis is conducted of high S/N ratio coude spectra for 12 Hyades dwarfs, together with solar spectra for comparison, in order to obtain accurate abundances for iron and other metals in the Hyades. Temperatures relative to the sun are derived from H-alpha wing profiles or broadband colors, and cluster stars are selected to bracket the solar temperature. Equivalent widths of metal lines are obtained by means of a profile fitting technique that accounts for blends, and many of the measured lines are noted to be sufficiently weak for uncertainties in microturbulence to be insignificant. The resulting iron abundances are anomalously low for two Hyades dwarfs, evidently due to high levels of chromospheric activity. Abundances are also obtained for 10 other elements. Title: The lithium abundance of Hyades main-sequence stars. Authors: Cayrel, R.; Cayrel de Strobel, G.; Campbell, B.; Dappen, W. Bibcode: 1984ApJ...283..205C Altcode: From high-quality Reticon spectra of Hyades G and K dwarfs, their lithium abundance is found to decline much more rapidly with decreasing temperature than heretofore realized. Previous observations of the 6707 Li I doublet for the cooler dwarfs have probably been contaminated by blends. However, the new lithium-temperature relation still does not agree with simple models of lithium burning in the convective zone, either with or without overshooting. Models have therefore to include other mechanisms for lithium depletion. Title: Spectroscopic evidence for starspots in the G dwarf HD1835. Authors: Campbell, B.; Cayrel, R. Bibcode: 1984ApJ...283L..17C Altcode: High signal-to-noise ratio spectra of HD 1835 (G2 V) reveal very weak lines of titanium oxide and calcium hydride. The authors show that these are unlikely to come from an M dwarf companion. The molecular lines probably originate in starspot umbrae, which cover about 3% of the stellar surface. Title: A Random Walk Approach to the Problem of Turbulent Diffusion and Lithium Destruction in Main-Sequence Stars Authors: Cayrel, R. Bibcode: 1984IAUS..105..533C Altcode: The author describes a way of computing the evolution of the lithium content in the convective zone of a main sequence star, using a random walk model for the mixing instead of the differential equation for diffusion. The advantage of this approach is that the finite scale of turbulent eddies can be taken into account. The burning rate of lithium increases so fast with temperature that it cannot be taken for granted that the free path of turbulent motions is small compared to the scale-height of the burning rate. Title: An Observational Test on Stellar Interior Mixing - the Lithium Depletion in Twelve Hyades Dwarfs Authors: Cayrel, R.; Cayrel, G.; Campbell, B.; Dappen, W. Bibcode: 1984IAUS..105..537C Altcode: No abstract at ADS Title: Knowledge acquired during the site testing for the Canada-France-Hawaii Telescope. Authors: Cayrel, R. Bibcode: 1984ESOC...18...45C Altcode: 1984stfl.work...45C The present discussion is mainly concerned with a wind-tunnel experiment which was conducted in connection with the task to select one out of three possible places on the summit of Mauna Kea for the 'Canada-France-Hawaii Telescope'. The considered 3.5-m telescope involved originally a purely French project, and, in a testing campaign, only French sites were initially considered. Details regarding this campaign are discussed, taking into account standard meteorological observations, seeing measurements, and photometric measurements. It was found, however, that the contemplated French sites could not provide the outstanding observational possibilities existing in certain foreign locations. After an extension of the search to prospective sites outside of France, it was eventually decided to locate the telescope on Mauna Kea in Hawaii. For the selection of a specific site, wind and turbulence conditions had to be considered. The informnation needed was obtained in tests in which a mock-up of the summit area was placed in a wind tunnel. Title: Steps towards the abundance scale I - the nearest open clusters. Authors: Cayrel, R.; Cayrel, G.; Campbell, B. Bibcode: 1983PASP...95S.587C Altcode: No abstract at ADS Title: The galactic globular cluster system : helium content versus metallicity. Authors: Caputo, F.; Cayrel, R.; Cayrel de Strobel, G. Bibcode: 1983A&A...123..135C Altcode: Theoretical constraints have been derived from recent stellar model computations and these have been compared with some observational parameters of galactic globular clusters. The objective was to obtain information on the helium versus metallicity relationship for these very old systems. The first result is that the disagreement between the Y-[Fe/H] relations derived by different authors with different methods can be resolved when the "canonical" frame is abandoned and the CNO content as well as the He-core masses is allowed to vary with [Fe/H]. Under these hypotheses the authors derive a unique Y-[Fe/H] relation whose actual slope depends on the value of the coefficient a = [CNO/Fe]/[Fe/H]. The implication of varying a is analyzed, particulary as concerns the ratio ΔY/ΔZ. It is found that acceptable values of the ratio ΔY/ΔZ may be attained when a = -0.5 to -0.6. Title: Evidence of high chromospheric activity in Hyades dwarfs from spectroscopic observations. Authors: Cayrel, R.; de Strobel, G. Cayrel; Campbell, B.; Mein, N.; Mein, P.; Dumont, S. Bibcode: 1983A&A...123...89C Altcode: The Hα Balmer line and the infrared Ca II triplet have been observed in two solar type dwarfs of the Hyades at the Coudé Spectrograph of the Canada-France-Hawaii Telescope. Noticeable differences appear in the cores of the lines between the stellar spectra and the solar spectrum (moonlight). These differences are ascribed to a more active chromosphere in the relatively young Hyades stars. Non-LTE computations show that the average disk of one of the Hyades dwarf is similar to a very bright element of the solar chromospheric network. Title: Book-Review - High Spectral Resolution in Astrophysics Authors: Cayrel, R.; Felenbok, P.; Notni, P. Bibcode: 1983AN....304..196C Altcode: No abstract at ADS Title: Search for population II giants up to 50 kiloparsecs from the sun. Authors: Cayrel, R.; Boulon, J. Bibcode: 1983MmSAI..54...95C Altcode: The results of an effort to segregate giants from dwarf stars cataloged in the RGU photometric survey performed by Becker (1965) are reported. A narrow-band filter centered on the MgI green triplet and the MgH green that yields a magnitude depressgd for dwarfs by 0.2 to 0.3 mag with respect to the giant stars were selected. The metal deficiency effect was computed within a factor of 100 for the equivalent width of the green line, with the finding that the metal deficiency decreases the equivalent width of the triplet by a factor of two. Therefore, giants within 100 kpc of the sun can be studied, and thereby the asymptotic density decrease of the galactic halo. A larger data base on the field halo giants can eventually permit derivation of radial velocities and improved estimations of the mass of the Galaxy. Title: Le télescope Canada-France-Hawaii. Authors: Cayrel, R. Bibcode: 1982LAstr..96..227C Altcode: The features, performance, and discoveries of the Canada-France-Hawaii 3.6m telescope located on Mauna Kea are described. The choice of design around 4 m was constrained by financial considerations, which are asserted to increase significantly in building larger instruments. The fused silicon primary lens resists thermal deformation and is capable of concentrating 50 percent of the received luminescence into a diameter of less than 0.2 arcsec. The telescope moves on a horseshoe track 10 m in diameter and has an axis of declination starting from 1/3 of the cradle. Computer controls automatically align the instrument and compensate for thermal changes in the structure. The objective also includes an f/8 secondary lens and an f/35 oscillating Cassegrain lens for IR viewing. Control of the microclimate which forms in the cupola is discussed. Title: Book-Review - High Spectral Resolution in Astrophysics - Applications to the Spatial Telescope Authors: Cayrel, R.; Felenbok, P.; Griffin, R. F. Bibcode: 1982Obs...102..155C Altcode: No abstract at ADS Title: Haute resolution spectrale en astrophysique: applications au Telescope Spatial. Deuxième Colloque National du Conseil Français du Telescope Spatial, Orsay, March 10 - 12 1981. Authors: Cayrel, R.; Felenbok, P. Bibcode: 1982hrse.book.....C Altcode: No abstract at ADS Title: Steps towards the abundance scale. I. The abundance of iron in the Hyades. Authors: Cayrel, R.; Cayrel de Strobel, G.; Campbell, B. Bibcode: 1981BAAS...13..926C Altcode: No abstract at ADS Title: Les problèmes de l'Astrophysique dont l'étude nécessite une haute résolution spectrale Authors: Cayrel, R. Bibcode: 1981hrse.conf....7C Altcode: No abstract at ADS Title: Haute resolution spectrale en astrophysique applications au telescope spatial Authors: Cayrel, Roger; Felenbok, Paul Bibcode: 1981hrse.conf.....C Altcode: No abstract at ADS Title: Etoiles de la branche horizontale. Authors: Cayrel, R. Bibcode: 1981ebds.conf...24C Altcode: No abstract at ADS Title: The Canada-France Telescope Authors: Cayrel, R. Bibcode: 1980Msngr..21....1C Altcode: The 3.6 m telescope of the Canada-France-Hawaii Corporation on the summit of Mauna Kea, on one of the Hawaiian islands, was put into operation last March. This nice instrument, located on what seems to be one of the best possible sites in the world, is presented to the readers of the Messenger by Dr. Roger Cayrel, director of the Corporation. Title: Small-Scale Versus Large-Scale Motions in the Solar Atmosphere Derived from a Non-Lte Calculation of Multiplet 38 OF Tii Authors: Cayrel, R.; Dumont, S.; Martin, P. Bibcode: 1980LNP...114..298C Altcode: 1980IAUCo..51..298C; 1980sttu.coll..298C No abstract at ADS Title: Book-Review - Bibliographical Star Index Authors: Cayrel, R.; Jung, J.; Kirchner, S.; Lahmek, R.; Ochsenbein, F.; Spite, F.; Valbousquet, A. Bibcode: 1980AN....301...99C Altcode: No abstract at ADS Title: Identification and Protection of Existing and Potential Observatory Sites Authors: Cayrel, R. Bibcode: 1979IAUTA..17a.215C Altcode: 1979IAUT...17..215C No abstract at ADS Title: Fine structure of the H-R diagram for 138 stars in the solar neighbourhood. Authors: Perrin, M. -N.; Hejlesen, P. M.; Cayrel de Strobel, G.; Cayrel, R. Bibcode: 1977A&A....54..779P Altcode: The evolution of a large number of stars in the solar neighborhood was studied on the basis of H-R diagrams converted to log T(eff), M(bol). Effective temperatures were based on reliable model-atmosphere computations, and reasonably accurate absolute bolometric magnitudes were obtained from absolute magnitudes of stars having well determined parallaxes and requiring small bolometric corrections. A special metal index was also evaluated for each star, in order to account for variation of metal content from star to star. The observational log T(eff), M(bol) diagrams are discussed in relation to the theoretical evolutionary and isochrone grids of Hejlesen (1975). The masses of the stars in the sample are estimated, and the ages of evolved stars are also estimated. A metal content versus age relation for disk stars is given. Title: Split of the Fe curve of growth as a function of atmospheric pressure. Authors: Cayrel, G.; Cayrel, R.; Foy, R. Bibcode: 1977A&A....54..797C Altcode: The intrinsic dispersion of the iron curve of growth is discussed for a subdwarf (Groombridge 1830), a dwarf (the sun), and a G 9 III giant (Epsilon Virginis). It is shown that this dispersion, which results in a splitting of the curve of growth, is due to a large scatter in the individual collisional damping constants of the lines. This scatter is largely greater than that predicted by the Van der Waals formula. The intrinsic dispersion of the curve of growth becomes larger with increasing atmospheric density of the star, and the point at which the intrinsic dispersion begins shifts for a dense subdwarf from the first turnoff up to the end of the plateau for a bright giant. If one does not take into account this phenomenon, systematic errors in the abundance determination occur, chiefly if no or only a few weak lines have been measured in a star. These errors may be as large as 0.30 dex and can alter the gravity determination. Title: Stellar atmospheres as indicator and factor of stellar evolution. Joint discussion at the XVIth General Assembly of the I.A.U., Grenoble, 1976. Authors: Cayrel, R.; Pagel, B. E. J. Bibcode: 1977HiA.....4B..99C Altcode: 1977HiA.....4...99C No abstract at ADS Title: Stellar atmospheres as indicator and factor of stellar evolution Authors: Cayrel, R.; Pagel, B. E. J. Bibcode: 1977saif.conf.....C Altcode: No abstract at ADS Title: Observational evidence for atmospheric physical characteristics relevant to stellar evolution. Authors: Cayrel, R.; Cayrel, G. Bibcode: 1977saif.conf..105C Altcode: No abstract at ADS Title: Editor's concluding remarks Authors: Cayrel, R. Bibcode: 1976pmas.conf..477C Altcode: No abstract at ADS Title: Theory of stellar atmospheres (Théorie des atmosphères stellaires). Authors: Cayrel, R.; Mihalas, D. Bibcode: 1976IAUTA..16b.189C Altcode: No abstract at ADS Title: Physique des mouvements dans les atmospheres stellaires Authors: Cayrel, R.; Steinberg, M. Bibcode: 1976pmas.conf.....C Altcode: 1976QB809.P48...... No abstract at ADS Title: Colors and ionization equilibria in K dwarfs. Authors: Perrin, M. N.; Cayrel de Strobel, G.; Cayrel, R. Bibcode: 1975A&A....39...97P Altcode: Summary. The strong discrepancy found by Oinas for K-dwarfs between the actual ionization ratio and its expected value derived from normal gravities and temperatures obtained by deblanketed scans has been reinvestigated for six stars of his program. It has not been found significant. Even in Oinas' analysis, if one eliminates entirely the sun as comparison star and one carries out an absolute curve of growth analysis, the discrepancy vanishes. In three other late-type stars not analysed by Oinas, the phenomenon was also not found to exist at an appreciable degree. Therefore it does not seem necessary any longer to look for a new continuous absorber to be introduced in the opacities of K stars in the 5000-10800 A spectral range. Key words: stellar atmospheres ionization equilibrium K-dwarfs Title: The Bibliographical Star Index Authors: Cayrel, R.; Jung, J.; Valbousquet, A. Bibcode: 1974BICDS...6...24C Altcode: No abstract at ADS Title: Bibliographical star index 1950-1976 Authors: Cayrel, R.; Jung, J.; Valbousquet, A. Bibcode: 1974bsi..book.....C Altcode: No abstract at ADS Title: Contribution to the study of supermetallicity in late-type giants. Authors: Blanc-Vaziaga, M. -J.; Cayrel, G.; Cayrel, R. Bibcode: 1973ApJ...180..871B Altcode: This research is a detailed analysis of Aur and Leo, two of the best examples of "super- metal-rich" (SMR) stars found by Spinrad and Taylor by a scanner technique. They have been analyzed on high-dispersion spectrograms taken at the 100-inch Mount Wilson coude' telescope (6.8 A mm-1) for Aur and at the coude' focus of the 60-inch ESO telescope in Chile (12 A mm-1) for Leo. The star E Vir has been used as a comparison star. Particular care has been taken only to compare spectrograms taken with the same instrumentation. The spectra have been interpreted with theoretical line computations using a grid of model atmospheres. The models have been calculated on the assumption of LTE, hydrostatic equilibrium, and radiative equilibrium. Convective transport in the convective zone has been taken into account. Line blanketing has been included using a statistical model of line absorption. The detailed analysis of Aur versus e Vir has not revealed any peculiarity other than a marginal deficiency of Aur in barium. With respect to the Sun, Aur has a mild overabundance of Na, as does E Vir; and a possible overabundance in Mg, Si, and Ca is just at the limit of significance. The analysis of Leo versus either E Vir or the Sun shows an overabundance in Na, Ca, Mn, and Cu and a deficiency in Ba. Iron and most other metals do not show any significant overabundance, even allowing for a rather larger uncertainty in the effective temperatures. The conclusion reached about "supermetallicity" is that the word "super-metal-rich" should be avoided, being misleading for stars which have a normal solar iron/hydrogen ratio. Supermetallicity appears to be highly selective, and limited to just a few elements. Subject headings:abundances, stellar - atmospheres, stellar - late-type stars - line profiles - stars, individual Title: Age from spectroscopic properties. Concluding remarks. Authors: Cayrel, R. Bibcode: 1973stag.conf...59C Altcode: 1973IAUCo..17...59C No abstract at ADS Title: Projets d'instrumentation pour le télescope de 3.60 m de l'I.N.A.G. Authors: Cayrel, R. Bibcode: 1972ailt.conf...91C Altcode: No abstract at ADS Title: Les spectrographes et l'électronographie. Authors: Combes, M.; Felenbok, P.; Picat, J. P.; Fort, B.; Cayrel, R. Bibcode: 1972ailt.conf..444C Altcode: No abstract at ADS Title: Concluding Remarks Authors: Cayrel, R. Bibcode: 1972ade..coll...59C Altcode: 1972IAUCo..17...59C No abstract at ADS Title: Project de télescope de l'I.N.A.G. Authors: Cayrel, R.; Belly, P. Y. Bibcode: 1971cltd.conf...59C Altcode: No abstract at ADS Title: Abundance of Helium in Stellar Atmospheres Authors: Cayrel, R. Bibcode: 1971HiA.....2..254C Altcode: No abstract at ADS Title: Abundance of helium in stellar atmospheres. Authors: Cayrel, R. Bibcode: 1971heun.conf..254C Altcode: No abstract at ADS Title: La composition chimique des étoiles Authors: Cayrel, R. Bibcode: 1970pfa..conf..126C Altcode: 1969pfa..conf..126C No abstract at ADS Title: Comparison of Synthetic Spectra with Real Spectra Authors: Cayrel, R. Bibcode: 1969tons.conf..237C Altcode: No abstract at ADS Title: The Location of a Few Subdwarfs in the Theoretical H-R Diagram and the Helium Content of Population II Authors: Cayrel, Roger Bibcode: 1968ApJ...151..997C Altcode: It is shown that photometric systems in which the line blocking is small enough to be accurately de- termined, like the GRI colors of Stebbins and Whitford, the vby colors of Stromgren, or the VRIJK colors of Johnson offer a more reliable way to obtain the effective temperature of subdwarfs than the UB V system. From the available data on these different systems, it is established that the main sequence of extreme subdwarfs, late enough to be unevolved, is below the main sequence of non-metal-poor stars by an amount of 0.7 ± 0.3 mag. The conclusion that extreme subdwarfs have a normal helium-to- hydrogen ratio seems unavoidable. Mild subdwarfs do not show any clear segregation from Population I, except perhaps /L Cassiopeiae. It is suggested that the smaller effect which should be observed for those stars is nearly cancelled by a residual evolution effect Title: Abundance Determinations from Stellar Spectra Authors: Cayrel, R.; Cayrel de Strobel, G. Bibcode: 1966ARA&A...4....1C Altcode: No abstract at ADS Title: Non-LTE Effects on Abundance Determination Authors: Cayrel, R. Bibcode: 1965SAOSR.174..453C Altcode: No abstract at ADS Title: Propriétés cinématiques et composition des étoiles Authors: Cayrel, R.; Kovalevsky, J. Bibcode: 1964LAstr..78..437C Altcode: 1964LAstr..78..437K No abstract at ADS Title: Theoretical Results on the Effect of Blanketing on T(τ) Authors: Cayrel, R. Bibcode: 1964SAOSR.167..139C Altcode: No abstract at ADS Title: On the Temperature of Radiative Equilibrium in a Layer of Optically Thin Gas in the Radiation Field of the Solar Photosphere Authors: Cayrel, R. Bibcode: 1964SAOSR.167..169C Altcode: No abstract at ADS Title: Les étoiles T Tauri Authors: Cayrel, R. Bibcode: 1963LAstr..77..229C Altcode: No abstract at ADS Title: Predicted fluxes and line intensities in late-type model atmospheres Authors: Cayrel, R.; Jugaku, Jun Bibcode: 1963AnAp...26..495C Altcode: No abstract at ADS Title: A Detailed Analysis of the Spectrum of Epsilon Virginis. Authors: Cayrel, Giusa; Cayrel, Roger Bibcode: 1963ApJ...137..431C Altcode: Lines in the spectral range X 4500-6700 A have been identified on tracings of the spectrum of E Virginis (G8 III). Three plates had a dispersion of 1 A/mm and five plates a dispersion of 2 8 A/mm. The equivalent widths of 1400 lines have been measured From the width of weak, unblended lines either a macroturbulence 3 6 + 1 km/sec, or a rotation, V sin i = 4 8 * 1 3 km/sec, can be derived The profile of the lines are not known with sufficient accuracy to favor one of these two extreme interpretations microturbulence of from 2 to 3 km/sec is derived from the curves of growth; there is a tendency to obtain a higher value for ionized lines than for neutral lines A detailed analysis of the atmosphere has been performed, leading to the values: T,j = 49400 K * 1500; log g = 2 7 * 0 2; and log A = log A0 + 0 2 (probable errors) There is a good agreement between the spectroscopic gravity and the value obtained from reasonable values of the mass and radius of the star The chemical composition of the atmosphere agrees with the solar composition within the probable error, except perhaps for Na No systematic enrichment in heavy-element abundance can be detected between the birth of the sun and that of E Virginis, about 10' years ago Higher accuracy is needed, both in equivalent width measurements and in the physical basis of the theory, to reveal any difference that might be less than a factor of 2 Title: L'abondance des métaux dans les vieilles étoiles de population I Authors: Cayrel, Roger. Bibcode: 1963NoPar...1...61C Altcode: No abstract at ADS Title: Sur quelques questions de la théorie des atmosphères stellaires. - II. Nouvelles formules d'approximation pour le calcul de l'intensité du rayonnement et du flux Authors: Cayrel, R. Bibcode: 1960AnAp...23..245C Altcode: No abstract at ADS Title: Sur quelques questions de la théorie des atmosphères stellaires. - I. Détermination de la gravité Authors: Cayrel, R. Bibcode: 1960AnAp...23..233C Altcode: No abstract at ADS Title: Model Atmospheres and Conventional Curve of Growth Analysis. Authors: Cayrel, Roger Bibcode: 1960AJ.....65R.486C Altcode: Possible systematic differences between abundances derived from the conventional curve of growth analysis and from detailed model atmosphere computations have been investigated. They have been found to be small, usually less than the sum of the errors arising from observational inaccuracy and incorrect assumptions in the theory. The main advantage of using models seems, therefore, to be confined to the use of more observational data to determine the physical parameters, temperature and gravity. Color, Balmer jump, and profiles of the Balmer lines are such examples. In addition, the use of models removes the uncertainty in the connection between the excitation and ionization temperatures. Supported by U.S. Air Force Office of Scientific Research under contract. Title: Zur Frage der Druckverbreiterung der solaren Balmerlinien. Mit 4 Textabbildungen Authors: Cayrel, R.; Traving, G. Bibcode: 1960ZA.....50..239C Altcode: No abstract at ADS Title: Grands et petits télescopes Authors: Cayrel, R. Bibcode: 1958LAstr..72..247C Altcode: No abstract at ADS Title: Observations et etudes theorique du spectre de XI Persei. Authors: Cayrel, R. Bibcode: 1958SAnAp....f...1C Altcode: No abstract at ADS Title: Observations et Étude Théorique du Spectre de Zeta Per Authors: Cayrel, Roger Bibcode: 1958SAnAp...6....5C Altcode: No abstract at ADS Title: Observations et étude théorique du spectre de ζ Per Title: Observations et étude théorique du spectre de ζ Per Title: Observations and theoretical study of the spectrum of ζ Per; Authors: Cayrel, Roger Bibcode: 1957PhDT........43C Altcode: No abstract at ADS Title: La polarisation de la lumiere par des poussieres de graphite et la polarisation interstellaire Authors: Schatzman, E.; Cayrel, R. Bibcode: 1955LIACo...6..601S Altcode: No abstract at ADS Title: Sur la polarisation interstellaire par des particules de graphite Authors: Cayrel, R.; Schatzman, E. Bibcode: 1954AnAp...17..555C Altcode: No abstract at ADS Title: Sur une cause d'erreur en spectrophotométrie Authors: Cayrel, Roger Bibcode: 1953AnAp...16..129C Altcode: No abstract at ADS Title: Relation largeur equivalente-profondeur centrale pour des raies d'absorption. Formulation analityque de la relation et comparaison avec l'observation Authors: Cayrel, R.; Taffara, S. Bibcode: 1953MmSAI..24..265C Altcode: No abstract at ADS Title: Effects secondaires renforçant une cause d'erreur en spectrophotométrie Authors: Cayrel, Roger Bibcode: 1953AnAp...16..466C Altcode: No abstract at ADS Title: Contributions à l'étude de l'équilibre radiatif Authors: Cayrel, Roger Bibcode: 1951AnAp...14....1C Altcode: No abstract at ADS