In the era of large spectroscopic surveys, massive databases of high-quality spectra provide tools to outline a new picture of our Galaxy. In this framework, an important piece of information is ...provided by our ability to infer stellar ages. We aim to provide empirical relations between stellar ages and abundance ratios for a sample of solar-like stars. We investigate the dependence on metallicity, and we apply our relations to Gaia-ESO samples of open clusters and field stars. We analyse high-resolution and high-S/N HARPS spectra of a sample of solar-like stars to obtain precise determinations of their atmospheric parameters and abundances through differential spectral analysis and age through isochrone fitting. We investigate the relations between ages and abundance ratios. For the abundance ratios with a steeper dependence on age, we perform multivariate linear regressions, including the dependence on metallicity. We apply our relations to a sample of open clusters located in 4<R\(_{GC}\)<16 kpc. Using them, we are able to recover the literature ages only for clusters located at R\(_{GC}\)>7 kpc. In these clusters, the content of s-elements is lower than expected from chemical evolution models, and consequently the s/\(\alpha\) are lower than in clusters of the same age located in the solar neighbourhood. With our chemical evolution model and a set of empirical yields, we suggest that a strong dependence on the star formation history and metallicity-dependent yields of s-elements can substantially modify the slope of the s/\(\alpha\)-Fe/H-age relation in different regions of the Galaxy. Our results point towards a non-universal relation s/\(\alpha\)-Fe/H-age, indicating the existence of relations at different R\(_{GC}\) or for different star formation history. A better understanding of the s-process at high metallicity is necessary to fully understand the origin of these variations.
Open clusters (OCs) are recognised as excellent tracers of Galactic thin-disc properties. At variance with intermediate-age and old OCs, for which a significant number of studies is now available, ...clusters younger than 150 Myr have been mostly overlooked in terms of their chemical composition, with few exceptions. On the other hand, previous investigations seem to indicate an anomalous behaviour of young clusters, which includes slightly sub-solar iron (Fe) abundances and extreme, unexpectedly high barium (Ba) enhancements. In a series of papers, we plan to expand our understanding of this topic and investigate whether these chemical peculiarities are instead related to abundance analysis techniques. We present a new determination of the atmospheric parameters for 23 dwarf stars observed by the Gaia-ESO survey in five young OCs (younger than 150 Myr) and one star-forming region (NGC 2264). We exploit a new method based on titanium (Ti) lines to derive the spectroscopic surface gravity, and most importantly, the microturbulence parameter. A combination of Ti I and Fe I lines is used to obtain effective temperatures. We also infer the abundances of Fe II, Ti II, Na I, Mg I, Al I, Si I, Ca I, Cr I and Ni I. Our findings are in fair agreement with Gaia-ESO iDR5 results for effective temperatures and surface gravities, but suggest that for very young stars, the microturbulence parameter is over-estimated when Fe lines are employed. This affects the derived chemical composition and causes the metal content of very young clusters to be under-estimated. Our clusters display a metallicity Fe/H between +0.04 and +0.12; they are not more metal poor than the Sun. Although based on a relatively small sample size, our explorative study suggests that we may not need to call for ad hoc explanations to reconcile the chemical composition of young OCs with Galactic chemical evolution models.
One of the aims of LSST is to perform a systematic survey of star clusters
and star forming regions (SFRs) in our Galaxy. In particular, the observations
obtained with LSST will make a big difference ...in Galactic regions that have
been poorly studied in the past, such as the anticenter and the disk beyond the
Galactic center, and they will have a strong impact in discovering new distant
SFRs. These results can be achieved by exploiting the exquisite depth that will
be attained if the wide-fast-deep (WFD) observing strategy of the main survey
is also adopted for the Galactic plane, in the g, r, and i filters.
In the era of large high-resolution spectroscopic surveys, high-quality spectra can contribute to our understanding of the Galactic chemical evolution, providing chemical abundances belonging to the ...different nucleosynthesis channels, and also providing constraints to stellar age. Some abundance ratios have been proven to be excellent indicators of stellar ages. We aim at providing an empirical relationship between stellar ages and C/N using, as calibrators, open star clusters observed by both the Gaia-ESO and APOGEE surveys. We use stellar parameters and abundances from the Gaia-ESO and APOGEE of the Galactic field and open cluster stars. Ages of star clusters are retrieved from the literature sources and validated using a common set of isochrones. We use the same isochrones to determine, for each age and metallicity, the surface gravity at which the first dredge-up and red giant branch bump occur. We study the effect of extra-mixing processes in our sample of giant stars, and we derive the mean C/N in evolved stars, including only stars without evidence of extra-mixing. Combining the Gaia-ESO and APOGEE samples of open clusters, we derive a linear relationship between C/N and logarithmic cluster ages. We apply our relationship to selected giant field stars in both Gaia-ESO and APOGEE. We find an age separation between thin and thick disc stars and age trends within their populations, with an increasing age towards lower metallicity populations. With such empirical relationship, we are able to provide an age estimate for giant stars in which C and N abundances are measured. Isochrone fitting is less sensitive for giant than dwarf stars at the turn off. The present method can be thus considered as an additional tool to give an independent estimate of the age of giant stars, with uncertainties in their ages comparable to those obtained using isochrone fitting for dwarf stars.
This paper compares the chemical evolution of the Large Magellanic Cloud (LMC) to that of the Milky Way (MW) and investigates the relation between the bar and the inner disc of the LMC in the context ...of the formation of the bar. We obtained high-resolution and mid signal-to-noise ratio spectra with FLAMES/GIRAFFE at ESO/VLT and performed a detailed chemical analysis of 106 and 58 LMC field red giant stars (mostly older than 1 Gyr), located in the bar and the disc of the LMC respectively. We measured elemental abundances for O, Mg, Si, Ca, Ti, Na, Sc, V, Cr, Co, Ni, Cu, Y, Zr, Ba, La and Eu. We find that the {\alpha}-element ratios Mg/Fe and O/Fe are lower in the LMC than in the MW while the LMC has similar Si/Fe, Ca/Fe, and Ti/Fe to the MW. As for the heavy elements, Ba,La/Eu exhibit a strong increase with increasing metallicity starting from Fe/H=-0.8 dex, and the LMC has lower Y+Zr/Ba+La ratios than the MW. Cu is almost constant over all metallicities and about 0.5 dex lower in the LMC than in the MW. The LMC bar and inner disc exhibit differences in their {\alpha}/Fe (slightly larger scatter for the bar in the metallicity range -1,-0.5), their Eu (the bar trend is above the disc trend for Fe/H > -0.5 dex), their Y and Zr, their Na and their V (offset between bar and disc distributions). Our results show that the chemical history of the LMC experienced a strong contribution from type Ia supernovae as well as a strong s-process enrichment from metal-poor AGB winds. Massive stars made a smaller contribution to the chemical enrichment compared to the MW. The observed differences between the bar and the disc speak in favour of an episode of enhanced star formation a few Gyr ago, occurring in the central parts of the LMC and leading to the formation of the bar. This is in agreement with recently derived star formation histories.
The Gaia-ESO Survey (GES) is a large spectroscopic survey that provides a unique opportunity to study the distribution of spectroscopic multiple systems among different populations of the Galaxy. We ...aim at detecting binarity/multiplicity for stars targeted by the GES from the analysis of the cross-correlation functions (CCFs) of the GES spectra with spectral templates. We develop a method based on the computation of the CCF successive derivatives to detect multiple peaks and determine their radial velocities, even when the peaks are strongly blended. The parameters of the detection of extrema (DOE) code have been optimized for each GES GIRAFFE and UVES setup to maximize detection. This code therefore allows to automatically detect multiple line spectroscopic binaries (SBn, n>1). We apply this method on the fourth GES internal data release and detect 354 SBn candidates (342 SB2, 11 SB3 and even one SB4), including only 9 SB2 known in the literature. This implies that about 98% of these SBn candidates are new (because of their faint visual magnitude that can reach V=19). Visual inspection of the SBn candidate spectra reveals that the most probable candidates have indeed a composite spectrum. Among SB2 candidates, an orbital solution could be computed for two previously unknown binaries: 06404608+0949173 (known as V642 Mon) in NGC 2264 and 19013257-0027338 in Berkeley 81. A detailed analysis of the unique SB4 (four peaks in the CCF) reveals that HD 74438 in the open cluster IC 2391 is a physically bound stellar quadruple system. The SB candidates belonging to stellar clusters are reviewed in detail to discard false detections. We warn against the use of atmospheric parameters for these system components rather than by SB-specific pipelines. Our implementation of an automatic detection of spectroscopic binaries within the GES has allowed an efficient discovery of many new multiple systems.
We exploited a sample of giant stars with Li measurements in Gaia-ESO IDR6 to investigate the evolution of A(Li) from the MSTO to the giant phase. We combined the Gaia-ESO data with Gaia EDR3 to ...obtain the distances and stellar luminosities. We compared our lithium abundances with literature values and found a good agreement. (4 data files).
Background: BRASS (Belgian Repository of Fundamental Atomic Data and Stellar Spectra) is an international networking project for the development of a new public database providing accurate ...fundamental atomic data of vital importance for stellar spectroscopic research. We present an overview of research results obtained in the past four years. Methods: The BRASS database offers atomic line data we thoroughly tested by comparing theoretical and observed stellar spectra. We perform extensive quality assessments of selected atomic input data using advanced radiative transfer spectrum synthesis calculations, which we compare to high-resolution Mercator-HERMES and ESO-VLT-UVES spectra of F-, G-, and K-type benchmark stars observed with very high signal-to-noise ratios. We have retrieved about half a million atomic lines required for our detailed spectrum synthesis calculations from the literature and online databases such as VAMDC, NIST, VALD, CHIANTI, Spectr-W 3 , TIPbase, TOPbase, SpectroWeb. Results: The atomic datasets have been cross-matched based on line electronic configuration information and organized in a new online repository called BRASS. The validated atomic data, combined with the observed and theoretical spectra are also interactively offered in BRASS. The combination of these datasets is a novel approach for its development providing a universal reference for advanced stellar spectroscopic research. Conclusion: We present an overview of the BRASS Data Interface developments allowing online user interaction for the combined spectrum and atomic data display, line identification, atomic data accuracy assessments including line log(gf)-values, and line equivalent width measurements.
In order to identify diagnostics distinguishing between pre- and post-mass-transfer systems, the mass-ratio distribution and period - eccentricity (P - e) diagram of barium and S stars are compared ...to those of the sample of binary red giants in open clusters from Mermilliod et al. (2007). From the analysis of the mass-ratio distribution for the cluster binary giants, we find an excess of systems with companion masses between 0.58 and 0.87 Msun, typical for white dwarfs. They represent 22% of the sample, which are thus candidate post-mass-transfer systems. Among these candidates which occupy the same locus as the barium and S stars in the (P-e) diagram, only 33% (= 4/12) show a chemical signature of mass transfer in the form of s-process overabundances (from rather moderate -- about 0.3 dex -- to more extreme -- about 1 dex). These s-process-enriched cluster stars show a clear tendency to be in the clusters with the lowest metallicity in the sample, confirming the classical prediction that the s-process nucleosynthesis is more efficient at low metallicities (the only strong barium star in our sample is found in the cluster with the lowest metallicity, i.e., star 173 in NGC 2420, with Fe/H = -0.26). The s-process overabundance is not clearly correlated with the cluster turnoff (TO) mass (such a correlation would instead hint at the importance of the dilution factor). We find as well a mild barium star in NGC 2335, a cluster with a large TO mass of 4.3 Msun, which implies that intermediate-mass AGB stars still operate the s-process and the third dredge-up.
Malgré des années de travaux théoriques et observationnels intensifs, nous sommes toujours loin d'une complète compréhension de l'univers proche, la Voie Lactée (MW) et ses galaxies voisines. Parmi ...les satellites de la MW, le Petit et le Grand Nuage de Magellan (LMC) sont particulièrement intéressants puisqu'ils forment le plus proche exemple de galaxies en interaction gravitationnelle et hydrodynamique, et partant, constituent un laboratoire unique pour étudier les effets des marées et l'échange de matière sur l'évolution chimique et l'histoire de la formation stellaire d'une galaxie. Le LMC est une galaxie de petite masse barrée à disque, prototype des galaxies riches en gaz que l'on pense jouer un rôle important dans la construction des grandes galaxies dans le cadre du ΛCDM. De plus, avec sa métallicité actuelle d'environ le tiers de la métallicité solaire, le chemin d'enrichissement chimique suivi par le LMC donne un grand poids aux yields des générations stellaires pauvres en métaux, ce qui fait du LMC un environnement idéal pour étudier la nucléosynthèse aux basses métallicités. Ce travail de doctorat vise à: 1) caractériser chimiquement la population de la barre du LMC, 2) comparer les tendances des éléments de la MW et du LMC et interpréter les différences ou ressemblance en termes d'évolution chimique et/ou de processus nucléosynthétiques (contraintes sur les sites et les processus nucléosynthétiques), 3) comparer l'évolution chimique de la barre et du disque interne du LMC et interpréter les différence ou ressemblance dans le contexte de la formation de la barre. Nos résultats montrent que l'histoire chimique du LMC a connu un forte contribution des supernovae de type I ainsi qu'un fort enrichissement en éléments s par les vents d'étoiles AGB pauvres en métaux. Par rapport à la MW, les étoiles massives ont eu une contribution plus petite à l'enrichissement chimique du LMC. Les différences observées entre la barre et le disque parlent en faveur d'un épisode de formation stellaire accrue il y a quelques Gyr, ayant lieu dans les zones centrales du LMC et conduisant à la formation de la barre. Ceci est en accord avec les histoires de la formation stellaire récemment dérivées.
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