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- ItemThe AMBRE Project: [Y/Mg] stellar dating calibration with Gaia(Les Ulis : EDP Sciences, 2019) Titarenko, A.; Recio-Blanco, A.; de Laverny, P.; Hayden, M.; Guiglion, G.Chemical abundance dating methods open new paths for temporal evolution studies of the Milky Way stellar populations. In this paper, we use a high spectral resolution database of turn-off stars in the solar neighbourhood to study the age dependence of the [Y/Mg] chemical abundance ratio. Our analysis reveals a clear correlation between [Y/Mg] and age for thin disc stars of different metallicities, in synergy with previous studies of solar-type stars. In addition, no metallicity dependence with stellar age is detected, allowing us to use the [Y/Mg] ratio as a reliable age proxy. Finally, the [Y/Mg]-age relation presents a discontinuity between thin and thick disc stars around 9-10 Gyr. For thick disc stars, the correlation has a different zero point and probably a steeper trend with age, reflecting the different chemical evolution histories of the two disc components.
- 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 AMBRE Project: r-process elements in the Milky Way thin and thick discs(Les Ulis : EDP Sciences, 2018) Guiglion, G.; de Laverny, P.; Recio-Blanco, A.; Prantzos, N.Context. The chemical evolution of neutron capture elements in the Milky Way disc is still a matter of debate. There is a lack of statistically significant catalogues of such element abundances, especially those of the r-process. Aims. We aim to understand the chemical evolution of r-process elements in Milky Way disc. We focus on three pure r-process elements Eu, Gd, and Dy. We also consider a pure s-process element, Ba, in order to disentangle the different nucleosynthesis processes. Methods. We take advantage of high-resolution FEROS, HARPS, and UVES spectra from the ESO archive in order to perform a homogeneous analysis on 6500 FGK Milky Way stars. The chemical analysis is performed thanks to the automatic optimization pipeline GAUGUIN. We present abundances of Ba (5057 stars), Eu (6268 stars), Gd (5431 stars), and Dy (5479 stars). Based on the [α/Fe] ratio determined previously by the AMBRE Project, we chemically characterize the thin and the thick discs, and a metal-rich α-rich population. Results. First, we find that the [Eu/Fe] ratio follows a continuous sequence from the thin disc to the thick disc as a function of the metallicity. Second, in thick disc stars, the [Eu/Ba] ratio is found to be constant, while the [Gd/Ba] and [Dy/Ba] ratios decrease as a function of the metallicity. These observations clearly indicate a different nucleosynthesis history in the thick disc between Eu and Gd-Dy. The [r/Fe] ratio in the thin disc is roughly around +0.1 dex at solar metallicity, which is not the case for Ba. We also find that the α-rich metal-rich stars are also enriched in r-process elements (like thick disc stars), but their [Ba/Fe] is very different from thick disc stars. Finally, we find that the [r/α] ratio tends to decrease with metallicity, indicating that supernovae of different properties probably contribute differently to the synthesis of r-process elements and α-elements. Conclusions. We provide average abundance trends for [Ba/Fe] and [Eu/Fe] with rather small dispersions, and for the first time for [Gd/Fe] and [Dy/Fe]. This data may help to constrain chemical evolution models of Milky Way r- and s-process elements and the yields of massive stars. We emphasize that including yields of neutron-star or black hole mergers is now crucial if we want to quantitatively compare observations to Galactic chemical evolution models.