| 1. |
- Gilmore, G., et al.
(författare)
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The Gaia-ESO Public Spectroscopic Survey : Motivation, implementation, GIRAFFE data processing, analysis, and final data products star
- 2022
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 666
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Tidskriftsartikel (refereegranskat)abstract
- Context. The Gaia-ESO Public Spectroscopic Survey is an ambitious project designed to obtain astrophysical parameters and elemental abundances for 100 000 stars, including large representative samples of the stellar populations in the Galaxy, and a well-defined sample of 60 (plus 20 archive) open clusters. We provide internally consistent results calibrated on benchmark stars and star clusters, extending across a very wide range of abundances and ages. This provides a legacy data set of intrinsic value, and equally a large wide-ranging dataset that is of value for the homogenisation of other and future stellar surveys and Gaia's astrophysical parameters. Aims. This article provides an overview of the survey methodology, the scientific aims, and the implementation, including a description of the data processing for the GIRAFFE spectra. A companion paper introduces the survey results. Methods. Gaia-ESO aspires to quantify both random and systematic contributions to measurement uncertainties. Thus, all available spectroscopic analysis techniques are utilised, each spectrum being analysed by up to several different analysis pipelines, with considerable effort being made to homogenise and calibrate the resulting parameters. We describe here the sequence of activities up to delivery of processed data products to the ESO Science Archive Facility for open use. Results. The Gaia-ESO Survey obtained 202 000 spectra of 115 000 stars using 340 allocated VLT nights between December 2011 and January 2018 from GIRAFFE and UVES. Conclusions. The full consistently reduced final data set of spectra was released through the ESO Science Archive Facility in late 2020, with the full astrophysical parameters sets following in 2022. A companion article reviews the survey implementation, scientific highlights, the open cluster survey, and data products.
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| 2. |
- Randich, S., et al.
(författare)
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The Gaia-ESO Public Spectroscopic Survey : Implementation, data products, open cluster survey, science, and legacy
- 2022
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Ingår i: Astronomy and Astrophysics. - : EDP SCIENCES S A. - 0004-6361 .- 1432-0746. ; 666
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Tidskriftsartikel (refereegranskat)abstract
- Context. In the last 15 years different ground-based spectroscopic surveys have been started (and completed) with the general aim of delivering stellar parameters and elemental abundances for large samples of Galactic stars, complementing Gaia astrometry. Among those surveys, the Gaia-ESO Public Spectroscopic Survey, the only one performed on a 8m class telescope, was designed to target 100 000 stars using FLAMES on the ESO VLT (both Giraffe and UVES spectrographs), covering all the Milky Way populations, with a special focus on open star clusters. Aims. This article provides an overview of the survey implementation (observations, data quality, analysis and its success, data products, and releases), of the open cluster survey, of the science results and potential, and of the survey legacy. A companion article reviews the overall survey motivation, strategy, Giraffe pipeline data reduction, organisation, and workflow. Methods. We made use of the information recorded and archived in the observing blocks; during the observing runs; in a number of relevant documents; in the spectra and master catalogue of spectra; in the parameters delivered by the analysis nodes and the working groups; in the final catalogue; and in the science papers. Based on these sources, we critically analyse and discuss the output and products of the Survey, including science highlights. We also determined the average metallicities of the open clusters observed as science targets and of a sample of clusters whose spectra were retrieved from the ESO archive. Results. The Gaia-ESO Survey has determined homogeneous good-quality radial velocities and stellar parameters for a large fraction of its more than 110 000 unique target stars. Elemental abundances were derived for up to 31 elements for targets observed with UVES. Lithium abundances are delivered for about 1/3 of the sample. The analysis and homogenisation strategies have proven to be successful; several science topics have been addressed by the Gaia-ESO consortium and the community, with many highlight results achieved. Conclusions. The final catalogue will be released through the ESO archive in the first half of 2022, including the complete set of advanced data products. In addition to these results, the Gaia-ESO Survey will leave a very important legacy, for several aspects and for many years to come.
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| 3. |
- Hourihane, A., et al.
(författare)
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The Gaia-ESO Survey : Homogenisation of stellar parameters and elemental abundances
- 2023
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 676
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Tidskriftsartikel (refereegranskat)abstract
- The Gaia-ESO Survey is a public spectroscopic survey that targeted greater than or similar to 10(5) stars covering all major components of the Milky Way from the end of 2011 to 2018, delivering its final public release in May 2022. Unlike other spectroscopic surveys, Gaia-ESO is the only survey that observed stars across all spectral types with dedicated, specialised analyses: from O (T-eff similar to 30 000-52 000 K) all the way to K-M (greater than or similar to 3500 K). The physics throughout these stellar regimes varies significantly, which has previously prohibited any detailed comparisons between stars of significantly different types. In the final data release (internal data release 6) of the Gaia-ESO Survey, we provide the final database containing a large number of products, such as radial velocities, stellar parameters and elemental abundances, rotational velocity, and also, for example, activity and accretion indicators in young stars and membership probability in star clusters for more than 114 000 stars. The spectral analysis is coordinated by a number of working groups (WGs) within the survey, each specialised in one or more of the various stellar samples. Common targets are analysed across WGs to allow for comparisons (and calibrations) amongst instrumental setups and spectral types. Here we describe the procedures employed to ensure all survey results are placed on a common scale in order to arrive at a single set of recommended results for use by all survey collaborators. We also present some general quality and consistency checks performed on the entirety of the survey results.
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| 4. |
- Baratella, M., et al.
(författare)
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The Gaia-ESO Survey: A new approach to chemically characterising young open cluster : II. Abundances of the neutron-capture elements Cu, Sr, Y, Zr, Ba, La, and Ce
- 2021
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 653
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Tidskriftsartikel (refereegranskat)abstract
- Context. Young open clusters (ages of less than 200 Myr) have been observed to exhibit several peculiarities in their chemical compositions. These anomalies include a slightly sub-solar iron content, super-solar abundances of some atomic species (e.g. ionised chromium), and atypical enhancements of [Ba/Fe], with values up to ~0.7 dex. Regarding the behaviour of the other s-process elements like yttrium, zirconium, lanthanum, and cerium, there is general disagreement in the literature: some authors claim that they follow the same trend as barium, while others find solar abundances at all ages. Aims. In this work we expand upon our previous analysis of a sample of five young open clusters (IC 2391, IC 2602, IC 4665, NGC 2516, and NGC 2547) and one star-forming region (NGC 2264), with the aim of determining abundances of different neutron-capture elements, mainly Cu I, Sr I, Sr II, Y II, Zr II, Ba II, La II, and Ce II. For NGC 2264 and NGC 2547 we present the measurements of these elements for the first time. Methods. We analysed high-resolution, high signal-to-noise spectra of 23 solar-type stars observed within the Gaia-ESO survey. After a careful selection, we derived abundances of isolated and clean lines via spectral synthesis computations and in a strictly differential way with respect to the Sun. Results. We find that our clusters have solar [Cu/Fe] within the uncertainties, while we confirm that [Ba/Fe] is super-solar, with values ranging from +0.22 to +0.64 dex. Our analysis also points to a mild enhancement of Y, with [Y/Fe] ratios covering values between 0 and +0.3 dex. For the other s-process elements we find that [X/Fe] ratios are solar at all ages. Conclusions. It is not possible to reconcile the anomalous behaviour of Ba and Y at young ages with standard stellar yields and Galactic chemical evolution model predictions. We explore different possible scenarios related to the behaviour of spectral lines, from the dependence on the different ionisation stages and the sensitivity to the presence of magnetic fields (through the Landé factor) to the first ionisation potential effect. We also investigate the possibility that they may arise from alterations of the structure of the stellar photosphere due to the increased levels of stellar activity that affect the spectral line formation, and consequently the derived abundances. These effects seem to be stronger in stars at ages of less than ∼ 100 Myr. However, we are still unable to explain these enhancements, and the Ba puzzle remains unsolved. With the present study we suggest that other elements, for example Sr, Zr, La, and Ce, might be more reliable tracer of the s-process at young ages, and we strongly encourage further critical observations.
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| 5. |
- Gutierrez Albarran, M. L., et al.
(författare)
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The Gaia-ESO Survey : Calibrating the lithium-age relation with open clusters and associations I. Cluster age range and initial membership selections
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 643
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Tidskriftsartikel (refereegranskat)abstract
- Context: Previous studies of open clusters have shown that lithium depletion is not only strongly age dependent but also shows a complex pattern with other parameters that is not yet understood. For pre- and main-sequence late-type stars, these parameters include metallicity, mixing mechanisms, convection structure, rotation, and magnetic activity.Aims: We perform a thorough membership analysis for a large number of stars observed within the Gaia-ESO survey (GES) in the field of 20 open clusters, ranging in age from young clusters and associations, to intermediate-age and old open clusters.Methods: Based on the parameters derived from the GES spectroscopic observations, we obtained lists of candidate members for each of the clusters in the sample by deriving radial velocity distributions and studying the position of the kinematic selections in the EW(Li)-versus-T-eff plane to obtain lithium members. We used gravity indicators to discard field contaminants and studied [Fe/H] metallicity to further confirm the membership of the candidates. We also made use of studies using recent data from the Gaia DR1 and DR2 releases to assess our member selections.Results: We identified likely member candidates for the sample of 20 clusters observed in GES (iDR4) with UVES and GIRAFFE, and conducted a comparative study that allowed us to characterize the properties of these members as well as identify field contaminant stars, both lithium-rich giants and non-giant outliers.Conclusions: This work is the first step towards the calibration of the lithium-age relation and its dependence on other GES parameters. During this project we aim to use this relation to infer the ages of GES field stars, and identify their potential membership to young associations and stellar kinematic groups of different ages.
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| 6. |
- Baratella, M., et al.
(författare)
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The Gaia-ESO Survey : a new approach to chemically characterising young open clusters I. Stellar parameters, and iron-peak, alpha-, and proton-capture elements
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP SCIENCES S A. - 0004-6361 .- 1432-0746. ; 634
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Tidskriftsartikel (refereegranskat)abstract
- Context: Open clusters are recognised as excellent tracers of Galactic thin-disc properties. At variance with intermediate-age and old open clusters, for which a significant number of studies is now available, clusters younger than less than or similar to 150 Myr have been mostly overlooked in terms of their chemical composition until recently (with few exceptions). On the other hand, previous investigations seem to indicate an anomalous behaviour of young clusters, which includes (but is not limited to) slightly sub-solar iron (Fe) abundances and extreme, unexpectedly high barium (Ba) enhancements.Aims: 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.Methods: We present a new determination of the atmospheric parameters for 23 dwarf stars observed by the Gaia-ESO survey in five young open clusters (tau < 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 and Fe lines is used to obtain effective temperatures. We also infer the abundances of Fe I, Fe II, Tit, Tin,Na I, Mg I, Al I,Sit, Ca I, Cr I, and Ni I.Results: 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.Conclusions: Our clusters display a metallicity [Fe/H] between +0.04 +/- 0.01 and +0.12 +/- 0.02; 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 open clusters with Galactic chemical evolution models.
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| 7. |
- Magrini, L., et al.
(författare)
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The Gaia-ESO survey : Mapping the shape and evolution of the radial abundance gradients with open clusters
- 2023
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 669
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Tidskriftsartikel (refereegranskat)abstract
- Context: The spatial distribution of elemental abundances and their time evolution are among the major constraints to disentangling the scenarios of formation and evolution of the Galaxy.Aims: In this paper we used the sample of open clusters available in the final release of the Gaia-ESO survey to trace the Galactic radial abundance and abundance-to-iron ratio gradients, and their time evolution.Methods: We selected member stars in 62 open clusters, with ages from 0.1 to about 7 Gyr, located in the Galactic thin disc at galactocentric radii (R-GC) from about 6 to 21 kpc. We analysed the shape of the resulting [Fe/H] gradient, the average gradients [El/H] and [El/Fe] combining elements belonging to four different nucleosynthesis channels, and their individual abundance and abundance ratio gradients. We also investigated the time evolution of the gradients dividing open clusters in three age bins.Results: The [Fe/H] gradient has a slope of -0.054 dex kpc(-1). It can be better approximated with a two-slope shape, steeper for R-GC <= 11.2 kpc and flatter in the outer regions. We saw different behaviours for elements belonging to different channels. For the time evolution of the gradient, we found that the youngest clusters (age < 1 Gyr) in the inner disc have lower metallicity than their older counterparts and that they outline a flatter gradient. We considered some possible explanations, including the effects of gas inflow and migration. We suggest that the most likely one may be related to a bias introduced by the standard spectroscopic analysis producing lower metallicities in the analysis of low-gravity stars.Conclusions: To delineate the shape of the 'true' gradient, we should most likely limit our analysis to stars with low surface gravity log g> 2.5 and microturbulent parameter xi< 1.8 km s(-1). Based on this reduced sample, we can conclude that the gradient has minimally evolved over the time-frame outlined by the open clusters, indicating a slow and stationary formation of the thin disc over the last 3 Gyr. We found a secondary role of cluster migration in shaping the gradient, with a more prominent role of migration for the oldest clusters.
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| 8. |
- Viscasillas Vázquez, C., et al.
(författare)
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The Gaia -ESO survey : Age-chemical-clock relations spatially resolved in the Galactic disc
- 2022
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 660
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Tidskriftsartikel (refereegranskat)abstract
- Context. The last decade has seen a revolution in our knowledge of the Galaxy thanks to the Gaia and asteroseismic space missions and the ground-based spectroscopic surveys. Aims. To complete this picture, it is necessary to map the ages of its stellar populations. During recent years, the dependence on time of abundance ratios involving slow (s) neutron-capture and α elements (called chemical-clocks) has been used to provide estimates of stellar ages, usually in a limited volume close to the Sun. We aim to analyse the relations of chemical clocks in the Galactic disc extending the range to RGC∼ 6- 20 kpc. Methods. Using the sixth internal data release of the Gaia-ESO survey, we calibrated several relations between stellar ages and abundance ratios [s/α] using a sample of open clusters, the largest one so far used with this aim (62 clusters). Thanks to their wide galactocentric coverage, we investigated the radial variations of the shape of these relations, confirming their non-universality. Results. The multi-variate relations allowed us to infer stellar ages for field stars. We estimated our accuracy (ranging from 0.0 to -0.9 Gyr) and precision (from 0.4 to 2.3 Gyr) in recovering the global ages of open clusters, and the ages of their individual members. We applied the relations with the highest correlation coefficients to the field star population, finding an older population at lower metallicity and higher [α/Fe] in the thin disc, and a younger one at higher [Fe/H] and low [α/Fe], as expected. Conclusion. We confirm that there is no single age-chemical clock relationship valid for the whole disc, but that there is a dependence on the galactocentric position, which is related to the radial variation of the star formation history combined with the non-monotonic dependence on metallicity of the yields of the s-process elements from low- and intermediate-mass stars. Finally, the abundance ratios [Ba/α] are more sensitive to age than those with [Y/α] for young disc stars, and their slopes vary less with galactocentric distance. We remind the reader that the application of such relationships to field stars is only of statistical value.
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| 9. |
- Casali, G., et al.
(författare)
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The Gaia-ESO survey : the non-universality of the age-chemical-clocks-metallicity relations in the Galactic disc
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 639
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Tidskriftsartikel (refereegranskat)abstract
- Context. In the era of large spectroscopic surveys, massive databases of high-quality spectra coupled with the products of the Gaia satellite 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, and consequently to sketch a Galactic timeline.Aims. We aim to provide empirical relations between stellar ages and abundance ratios for a sample of stars with very similar stellar parameters to those of the Sun, namely the so-called solar-like stars. We investigate the dependence on metallicity, and we apply our relations to independent samples, that is, the Gaia-ESO samples of open clusters and of field stars.Methods. We analyse high-resolution and high-signal-to-noise-ratio HARPS spectra of a sample of solar-like stars to obtain precise determinations of their atmospheric parameters and abundances for 25 elements and/or ions belonging to the main nucleosynthesis channels through differential spectral analysis, and of their ages through isochrone fitting.Results. We investigate the relations between stellar ages and several abundance ratios. For the abundance ratios with a steeper dependence on age, we perform multivariate linear regressions, in which we include the dependence on metallicity, [Fe/H]. We apply our best relations to a sample of open clusters located from the inner to the outer regions of the Galactic disc. Using our relations, we are able to recover the literature ages only for clusters located at R-GC > 7 kpc. The values that we obtain for the ages of the inner-disc clusters are much greater than the literature ones. In these clusters, the content of neutron capture elements, such as Y and Zr, is indeed lower than expected from chemical evolution models, and consequently their [Y/Mg] and [Y/Al] 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 stellar yields of s-process elements can substantially modify the slope of the [s/alpha]-[Fe/H]-age relation in different regions of the Galaxy.Conclusions. Our results point towards a non-universal relation [s/alpha]-[Fe/H]-age, indicating the existence of relations with different slopes and intercepts at different Galactocentric distances or for different star formation histories. Therefore, relations between ages and abundance ratios obtained from samples of stars located in a limited region of the Galaxy cannot be translated into general relations valid for the whole disc. A better understanding of the s-process at high metallicity is necessary to fully understand the origin of these variations.
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| 10. |
- Merle, T., et al.
(författare)
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The Gaia -ESO Survey : Detection and characterisation of single-line spectroscopic binaries
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 635
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Tidskriftsartikel (refereegranskat)abstract
- Context: Multiple stellar systems play a fundamental role in the formation and evolution of stellar populations in galaxies. Recent and ongoing large ground-based multi-object spectroscopic surveys significantly increase the sample of spectroscopic binaries (SBs) allowing analyses of their statistical properties. Aims: We investigate the repeated spectral observations of the Gaia-ESO Survey internal data release 5 (GES iDR5) to identify and characterise SBs with one visible component (SB1s) in fields covering mainly the discs, the bulge, the CoRot fields, and some stellar clusters and associations. Methods: A statistical X2-test is performed on spectra of the iDR5 subsample of approximately 43 500 stars characterised by at least two observations and a signal-to-noise ratio larger than three. In the GES iDR5, most stars have four observations generally split into two epochs. A careful estimation of the radial velocity (RV) uncertainties is performed. Our sample of RV variables is cleaned from contamination by pulsation- and/or convection-induced variables using Gaia DR2 parallaxes and photometry. Monte-Carlo simulations using the SB9 catalogue of spectroscopic orbits allow to estimate our detection effciency and to correct the SB1 rate to evaluate the GES SB1 binary fraction and its relation to effective temperature and metallicity. Result: We find 641 (resp., 803) FGK SB1 candidates at the 5σ (resp., 3σ) level. The maximum RV differences range from 2.2 km s-1 at the 5σ confidence level (1.6 km s-1 at 3σ) to 133 km s-1 (in both cases). Among them a quarter of the primaries are giant stars and can be located as far as 10 kpc. The orbital-period distribution is estimated from the RV standard-deviation distribution and reveals that the detected SB1s probe binaries with log P[d] / 4. We show that SB1s with dwarf primaries tend to have shorter orbital periods than SB1s with giant primaries. This is consistent with binary interactions removing shorter period systems as the primary ascends the red giant branch. For two systems, tentative orbital solutions with periods of 4 and 6 d are provided. After correcting for detection efficiency, selection biases, and the present-day mass function, we estimate the global GES SB1 fraction to be in the range 7-14% with a typical uncertainty of 4%. A small increase of the SB1 frequency is observed from K- towards F-type stars, in agreement with previous studies. The GES SB1 frequency decreases with metallicity at a rate of (-9 ± 3)% dex-1 in the metallicity range -2:7 ≤ [Fe=H] ≤ +0:6. This anticorrelation is obtained with a confidence level higher than 93% on a homogeneous sample covering spectral types FGK and a large range of metallicities. When the present-day mass function is accounted for, this rate turns to (-4 ± 2)% dex-1 with a confidence level higher than 88%. In addition we provide the variation of the SB1 fraction with metallicity separately for F, G, and K spectral types, as well as for dwarf and giant primaries.
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