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- ItemThe metal-poor end of the Spite plateau: II. Chemical and dynamical investigation(Les Ulis : EDP Sciences, 2021) Matas Pinto, A. M.; Spite, M.; Caffau, E.; Bonifacio, P.; Sbordone, L.; Sivarani, T.; Steffen, M.; Spite, F.; François, P.; Di Matteo, P.Context. The study of old, metal-poor stars deepens our knowledge on the early stages of the universe. In particular, the study of these stars gives us a valuable insight into the masses of the first massive stars and their emission of ionising photons. Aims. We present a detailed chemical analysis and determination of the kinematic and orbital properties of a sample of 11 dwarf stars. These are metal-poor stars, and a few of them present a low lithium content. We inspected whether the other elements also present anomalies. Methods. We analysed the high-resolution UVES spectra of a few metal-poor stars using the Turbospectrum code to synthesise spectral lines profiles. This allowed us to derive a detailed chemical analysis of Fe, C, Li, Na, Mg, Al, Si, CaI, CaII, ScII, TiII, Cr, Mn, Co, Ni, Sr, and Ba. Results. We find excellent coherence with the reference metal-poor First Stars sample. The lithium-poor stars do not present any anomaly of the abundance of the elements other than lithium. Among the Li-poor stars, we show that CS 22882-027 is very probably a blue-straggler. The star CS 30302-145, which has a Li abundance compatible with the plateau, has a very low Si abundance and a high Mn abundance. In many aspects, it is similar to the α-poor star HE 1424-0241, but it is less extreme. It could have been formed in a satellite galaxy and later been accreted by our Galaxy. This hypothesis is also supported by its kinematics.
- ItemThe Gaia -ESO Survey: Lithium measurements and new curves of growth(Les Ulis : EDP Sciences, 2022) Franciosini, E.; Randich, S.; de Laverny, P.; Biazzo, K.; Feuillet, D.K.; Frasca, A.; Lind, K.; Prisinzano, L.; Tautvaišiene, G.; Lanzafame, A.C.; Smiljanic, R.; Gonneau, A.; Magrini, L.; Pancino, E.; Guiglion, G.; Sacco, G.G.; Sanna, N.; Gilmore, G.; Bonifacio, P.; Jeffries, R.D.; Micela, G.; Prusti, T.; Alfaro, E.J.; Bensby, T.; Bragaglia, A.; François, P.; Korn, A.J.; Van Eck, S.; Bayo, A.; Bergemann, M.; Carraro, G.; Heiter, U.; Hourihane, A.; Jofré, P.; Lewis, J.; Martayan, C.; Monaco, L.; Morbidelli, L.; Worley, C.C.; Zaggia, S.Context. The Gaia-ESO Survey (GES) is a large public spectroscopic survey that was carried out using the multi-object FLAMES spectrograph at the Very Large Telescope. The survey provides accurate radial velocities, stellar parameters, and elemental abundances for ~115 000 stars in all Milky Way components. Aims. In this paper, we describe the method adopted in the final data release to derive lithium equivalent widths (EWs) and abundances. Methods. Lithium EWs were measured using two different approaches for FGK and M-type stars, to account for the intrinsic differences in the spectra. For FGK stars, we fitted the lithium line using Gaussian components, while direct integration over a predefined interval was adopted for M-type stars. Care was taken to ensure continuity between the two regimes. Abundances were derived using a new set of homogeneous curves of growth that were derived specifically for GES, and which were measured on a synthetic spectral grid consistently with the way the EWs were measured. The derived abundances were validated by comparison with those measured by other analysis groups using different methods. Results. Lithium EWs were measured for ~40 000 stars, and abundances could be derived for ~38 000 of them. The vast majority of the measures (80%) have been obtained for stars in open cluster fields. The remaining objects are stars in globular clusters, or field stars in the Milky Way disc, bulge, and halo. Conclusions. The GES dataset of homogeneous lithium abundances described here will be valuable for our understanding of several processes, from stellar evolution and internal mixing in stars at different evolutionary stages to Galactic evolution.
- ItemThe solar photospheric silicon abundance according to CO5BOLD: Investigating line broadening, magnetic fields, and model effects(Les Ulis : EDP Sciences, 2022) Deshmukh, S.A.; Ludwig, H.-G.; Kučinskas, A.; Steffen, M.; Barklem, P.S.; Caffau, E.; Dobrovolskas, V.; Bonifacio, P.Context. In this work, we present a photospheric solar silicon abundance derived using CO5BOLD model atmospheres and the LINFOR3D spectral synthesis code. Previous works have differed in their choice of a spectral line sample and model atmosphere as well as their treatment of observational material, and the solar silicon abundance has undergone a downward revision in recent years. We additionally show the effects of the chosen line sample, broadening due to velocity fields, collisional broadening, model spatial resolution, and magnetic fields. Aims. Our main aim is to derive the photospheric solar silicon abundance using updated oscillator strengths and to mitigate model shortcomings such as over-broadening of synthetic spectra. We also aim to investigate the effects of different line samples, fitting configurations, and magnetic fields on the fitted abundance and broadening values. Methods. CO5BOLD model atmospheres for the Sun were used in conjunction with the LINFOR3D spectral synthesis code to generate model spectra, which were then fit to observations in the Hamburg solar atlas. We took pixel-to-pixel signal correlations into account by means of a correlated noise model. The choice of line sample is crucial to determining abundances, and we present a sample of 11 carefully selected lines (from an initial choice of 39 lines) in both the optical and infrared, which has been made possible with newly determined oscillator strengths for the majority of these lines. Our final sample includes seven optical Si i lines, three infrared Si i lines, and one optical Si ii line. Results. We derived a photospheric solar silicon abundance of log ϵSi = 7.57 ± 0.04, including a - 0.01 dex correction from Non-Local Thermodynamic Equilibrium (NLTE) effects. Combining this with meteoritic abundances and previously determined photospheric abundances results in a metal mass fraction Z/X = 0.0220 ± 0.0020. We found a tendency of obtaining overly broad synthetic lines. We mitigated the impact of this by devising a de-broadening procedure. The over-broadening of synthetic lines does not substantially affect the abundance determined in the end. It is primarily the line selection that affects the final fitted abundance.
- ItemMINCE: I. Presentation of the project and of the first year sample(Les Ulis : EDP Sciences, 2022) Cescutti, G.; Bonifacio, P.; Caffau, E.; Monaco, L.; Franchini, M.; Lombardo, L.; Matas Pinto, A. M.; Lucertini, F.; François, P.; Spitoni, E.; Lallement, R.; Sbordone, L.; Mucciarelli, A.; Spite, M.; Hansen, C.J.; Di Marcantonio, P.; Kučinskas, A.; Dobrovolskas, V.; Korn, A.J.; Valentini, M.; Magrini, L.; Cristallo, S.; Matteucci, F.Context. In recent years, Galactic archaeology has become a particularly vibrant field of astronomy, with its main focus set on the oldest stars of our Galaxy. In most cases, these stars have been identified as the most metal-poor. However, the struggle to find these ancient fossils has produced an important bias in the observations - in particular, the intermediate metal-poor stars (-2.5 < [Fe/H] <-1.5) have been frequently overlooked. The missing information has consequences for the precise study of the chemical enrichment of our Galaxy, in particular for what concerns neutron capture elements and it will be only partially covered by future multi object spectroscopic surveys such as WEAVE and 4MOST. Aims. Measuring at Intermediate Metallicity Neutron Capture Elements (MINCE) is gathering the first high-quality spectra (high signal-to-noise ratio, S/N, and high resolution) for several hundreds of bright and metal-poor stars, mainly located in our Galactic halo. Methods. We compiled our selection mainly on the basis of Gaia data and determined the stellar atmospheres of our sample and the chemical abundances of each star. Results. In this paper, we present the first sample of 59 spectra of 46 stars. We measured the radial velocities and computed the Galactic orbits for all stars. We found that 8 stars belong to the thin disc, 15 to disrupted satellites, and the remaining cannot be associated to the mentioned structures, and we call them halo stars. For 33 of these stars, we provide abundances for the elements up to zinc. We also show the chemical evolution results for eleven chemical elements, based on recent models. Conclusions. Our observational strategy of using multiple telescopes and spectrographs to acquire high S/N and high-resolution spectra for intermediate-metallicity stars has proven to be very efficient, since the present sample was acquired over only about one year of observations. Finally, our target selection strategy, after an initial adjustment, proved satisfactory for our purposes.
- ItemThe Gaia RVS benchmark stars: I. Chemical inventory of the first sample of evolved stars and its Rb NLTE investigation(Les Ulis : EDP Sciences, 2021) Caffau, E.; Bonifacio, P.; Korotin, S.A.; François, P.; Lallement, R.; Matas Pinto, A.M.; Di Matteo, P.; Steffen, M.; Mucciarelli, A.; Katz, D.; Haywood, M.; Chemin, L.; Sartoretti, P.; Sbordone, L.; Andrievsky, S.M.; Kovtyukh, V.V.; Spite, M.; Spite, F.; Panuzzo, P.; Royer, F.; Thévenin, F.; Ludwig, H.-G.; Marchal, O.; Plum, G.Context. The Radial Velocity Spectrometer (RVS) on board the Gaia satellite is not provided with a wavelength calibration lamp. It uses its observations of stars with known radial velocity to derive the dispersion relation. To derive an accurate radial velocity calibration, a precise knowledge of the line spread function (LSF) of the RVS is necessary. Good-quality ground-based observations in the wavelength range of the RVS are highly desired to determine the LSF. Aims. Several radial velocity standard stars are available to the Gaia community. The highest possible number of calibrators will surely allow us to improve the accuracy of the radial velocity. Because the LSF may vary across the focal plane of the RVS, a large number of high-quality spectra for the LSF calibration may allow us to better sample the properties of the focal plane. Methods. We selected a sample of stars to be observed with UVES at the Very Large Telescope, in a setting including the wavelength range of RVS, that are bright enough to allow obtaining high-quality spectra in a short time. We also selected stars that lack chemical investigation in order to increase the sample of bright, close by stars with a complete chemical inventory. Results. We here present the chemical analysis of the first sample of 80 evolved stars. The quality of the spectra is very good, therefore we were able to derive abundances for 20 elements. The metallicity range spanned by the sample is about 1 dex, from slightly metal-poor to solar metallicity. We derived the Rb abundance for all stars and investigated departures from local thermodynamical equilibrium (NLTE) in the formation of its lines. Conclusions. The sample of spectra is of good quality, which is useful for a Gaia radial velocity calibration. The Rb NLTE effects in this stellar parameters range are small but sometimes non-negligible, especially for spectra of this good quality.