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Context. Large spectroscopic surveys devoted to the study of the Milky Way, including Gaia, use automated pipelines to massively determine the atmospheric parameters of millions of stars. The Gaia FGK Benchmark Stars are reference stars with Teff and log g derived through fundamental relations, independently of spectroscopy, to be used as anchors for the parameter scale. The first and second versions of the sample have been extensively used for that purpose, and more generally to help constrain stellar models. Aims. We provide the third version of the Gaia FGK Benchmark Stars, an extended set intended to improve the calibration of spectroscopic surveys, and their interconnection. Methods. We have compiled about 200 candidates which have precise measurements of angular diameters and parallaxes. We determined their bolometric fluxes by fitting their spectral energy distribution. Masses were determined using two sets of stellar evolution models. In a companion paper we describe the determination of metallicities and detailed abundances. Results. We provide a new set of 192 Gaia FGK Benchmark Stars with their fundamental Teff and logg, and with uncertainties lower than 2% for most stars. Compared to the previous versions, the homogeneity and accuracy of the fundamental parameters are significantly improved thanks to the high quality of the Gaia data reflecting on distances and bolometric fluxes., Comment: accepted in A&A

WEAVE, the new wide-field, massively multiplexed spectroscopic survey facility for the William Herschel Telescope, will see first light in late 2022. WEAVE comprises a new 2-degree field-of-view prime-focus corrector system, a nearly 1000-multiplex fibre positioner, 20 individually deployable 'mini' integral field units (IFUs), and a single large IFU. These fibre systems feed a dual-beam spectrograph covering the wavelength range 366$-$959\,nm at $R\sim5000$, or two shorter ranges at $R\sim20\,000$. After summarising the design and implementation of WEAVE and its data systems, we present the organisation, science drivers and design of a five- to seven-year programme of eight individual surveys to: (i) study our Galaxy's origins by completing Gaia's phase-space information, providing metallicities to its limiting magnitude for $\sim$3 million stars and detailed abundances for $\sim1.5$ million brighter field and open-cluster stars; (ii) survey $\sim0.4$ million Galactic-plane OBA stars, young stellar objects and nearby gas to understand the evolution of young stars and their environments; (iii) perform an extensive spectral survey of white dwarfs; (iv) survey $\sim400$ neutral-hydrogen-selected galaxies with the IFUs; (v) study properties and kinematics of stellar populations and ionised gas in $z<0.5$ cluster galaxies; (vi) survey stellar populations and kinematics in $\sim25\,000$ field galaxies at $0.3\lesssim z \lesssim 0.7$; (vii) study the cosmic evolution of accretion and star formation using $>1$ million spectra of LOFAR-selected radio sources; (viii) trace structures using intergalactic/circumgalactic gas at $z>2$. Finally, we describe the WEAVE Operational Rehearsals using the WEAVE Simulator., Comment: 41 pages, 27 figures, accepted for publication by MNRAS; updated version including information on individual grants in a revised Acknowledgements section, corrections to the affiliation list, and an updated references list

The recently re-discovered open cluster Stock 2, located roughly 375 pc away and about 400 Myr old, has the potential to be an exciting new testbed for our understanding of stellar evolution. We present results from a spectroscopic campaign to characterize stars near the cluster's main-sequence turnoff; our goal is to identify candidate chemically peculiar stars among the cluster's A stars. We obtained echelle spectra for 64 cluster members with ESPaDOnS on the 3.6-m Canada-France-Hawaii Telescope, Mauna Kea Observatory, USA, and for six stars with SOPHIE on the 1.93-m telescope at the Observatoire de Haute-Provence, France. We complemented these new observations with those of 13 high-mass cluster members from the HARPS-N archive; our overall sample is of 71 stars. We derived the fundamental parameters (Teff, log g, [M/H]) as well as vsini for our sample using the Sliced Inverse Regression (SIR) technique, and then used iSpec to derive individual abundances of 12 chemical species. With these abundance determinations, we identified nine A stars with anomalous levels of Sc, Ca, and other metallic lines. Follow-up observations of these Am candidates with a known age can transform them into benchmarks for evolutionary models that include atomic diffusion and help build a better understanding of the complex interactions between macroscopic and microscopic processes in stellar interiors., Comment: Accepted for publication in AJ

The number of stars with a measured value of [Fe/H] is considerably increasing thanks to spectroscopic surveys. However different methodologies, inputs and assumptions used in spectral analyses lead to different precisions in [Fe/H] and possibly to systematic differences that need to be evaluated. It is essential to understand the characteristics of each survey to fully exploit their potential, in particular if the surveys are combined. The purpose of this study is to compare [Fe/H] determinations from the largest spectroscopic surveys (APOGEE, GALAH, the Gaia ESO survey, RAVE, LAMOST, SEGUE ) to other catalogues taken as reference. Offsets and dispersions of the residuals are examined as well as their trends with other parameters. We use reference samples providing independent determinations of [Fe/H] which are compared to those from the surveys for common stars. The distribution of the residuals is assessed through simple statistics that measures the offset between two catalogues and the dispersion representative of the precision of both catalogues. When relevant, linear fits are performed. A large sample of FGK-type stars with [Fe/H] based on high-resolution, high signal to noise spectroscopy was built from the PASTEL catalogue to provide a reference sample. We also use FGK members in open and globular clusters to assess the internal consistency of [Fe/H] of each survey. The agreement of median [Fe/H] values for clusters observed by different surveys is discussed. All the surveys overestimate the low metallicities, and some of them also underestimate the high metallicities. They perform well in the most populated intermediate metallicity range, whatever the resolution. In most cases the typical precision that we deduce from the comparisons is in good agreement with the uncertainties quoted in the catalogues. Some exceptions to this general behaviour are discussed., Comment: accepted in A&A

We present new observational data for the heavy elements molybdenum (Mo, Z = 42) and ruthenium (Ru, Z = 44) in F-, G-, and K-stars belonging to different substructures of the Milky Way. The range of metallicity covered is --1.0 $<$ [Fe/H] $<$ +0.3. The spectra of Galactic disc stars have a high resolution of 42,000 and 75,000 and signal-to-noise ratio better than 100. Mo and Ru abundances were derived by comparing the observed and synthetic spectra in the region of Mo I lines at 5506, 5533 \AA~ for 209 stars and Ru I lines at 4080, 4584, 4757 \AA~ for 162 stars using the LTE approach. For all the stars, the Mo and Ru abundance determinations are obtained for the first time with an average error of 0.14 dex. This is the first extended sample of stellar observations for Mo and Ru in the Milky Way disc, and together with earlier observations in halo stars it is pivotal in providing a complete picture of the evolution of Mo and Ru across cosmic timescales. The Mo and Ru abundances were compared with those of the neutron-capture elements (Sr, Y, Zr, Ba, Sm, Eu). The complex nucleosynthesis history of Mo and Ru is compared with different Galactic Chemical Evolution (GCE) simulations. In general, present theoretical GCE simulations show underproduction of Mo and Ru at all metallicities compared to observations. This highlights a significant contribution of nucleosynthesis processes not yet considered in our simulations. A number of possible scenarios are discussed., Comment: 23 pages, 12 figures, 7 tables, accepted in MNRAS

There has been an incredibly large investment in obtaining high-resolution stellar spectra for determining chemical abundances of stars. This information is crucial to answer fundamental questions in Astronomy by constraining the formation and evolution scenarios of the Milky Way as well as the stars and planets residing in it. We have just entered a new era, in which chemical abundances of FGK-type stars are being produced at industrial scales, where the observations, reduction, and analysis of the data are automatically performed by machines. Here we review the latest human efforts to assess the accuracy and precision of such industrial abundances by providing insights in the steps and uncertainties associated with the process of determining stellar abundances. To do so, we highlight key issues in the process of spectral analysis for abundance determination, with special effort in disentangling sources of uncertainties. We also provide a description of current and forthcoming spectroscopic surveys, focusing on their reported abundances and uncertainties. This allows us to identify which elements and spectral lines are best and why. Finally, we make a brief selection of main scientific questions the community is aiming to answer with abundances., Comment: Accepted by Annual Review of Astronomy & Astrophysics, Volume 57, copyright Annual Reviews

The Gaia FGK benchmark stars are among the preferred samples of reference stars to test parametrisation pipelines of spectroscopic surveys. They consist of a small but carefully selected sample whose parameters are derived consistently and homogeneously. Here we summarise this work and provide our current list of stars with associated parameters which are recommended for validation and calibration purposes for stellar surveys. Data available at CDS as catalog III/281., Comment: published in RNAAS

Stellar elemental abundances are important for understanding the fundamental properties of a star or stellar group, such as age and evolutionary history, as well as the composition of an orbiting planet. However, as abundance measurement techniques have progressed, there has been little standardization between individual methods and their comparisons. As a result, different stellar abundance procedures determine measurements that vary beyond quoted error for the same elements within the same stars (Hinkel et al. 2014). The purpose of this paper is to better understand the systematic variations between methods and offer recommendations for producing more accurate results in the future. We have invited a number of participants from around the world (Australia, Portugal, Sweden, Switzerland, and USA) to calculate ten element abundances (C, O, Na, Mg, Al, Si, Fe, Ni, Ba, and Eu) using the same stellar spectra for four stars (HD361, HD10700, HD121504, HD202206). Each group produced measurements for each of the stars using: 1) their own autonomous techniques, 2) standardized stellar parameters, 3) standardized line list, and 4) both standardized parameters and line list. We present the resulting stellar parameters, absolute abundances, and a metric of data similarity that quantifies homogeneity of the data. We conclude that standardization of some kind, particularly stellar parameters, improves the consistency between methods. However, because results did not converge as more free parameters were standardized, it is clear there are inherent issues within the techniques that need to be reconciled. Therefore, we encourage more conversation and transparency within the community such that stellar abundance determinations can be reproducible as well as accurate and precise., Comment: 86 pages, 5 figures, 24 tables, accepted to Astrophysical Journal Supplement

Since the release of the Hipparcos catalog in 1997, the distance to the Pleiades open cluster has been heavily debated. The distance obtained from Hipparcos and those by alternative methods differ by 10 to 15 %. As accurate stellar distances are key to understanding stellar structure and evolution, this dilemma puts the validity of stellar evolution models into question. Using our model-independent method to determine parallaxes based on twin stars, we report individual parallaxes of 15 FGK type stars in the Pleiades in anticipation of the astrometric mission Gaia. These parallaxes give a mean cluster parallax of $7.42\pm0.09~\mathrm{mas}$ corresponding to a mean cluster distance of ${ 134.8\pm 1.7~\mathrm{pc}}$. This value agrees with the current results obtained from stellar evolution models., Comment: refereed version, accepted for publication in A&A

We have entered an era of large spectroscopic surveys in which we can measure, through automated pipelines, the atmospheric parameters and chemical abundances for large numbers of stars. Calibrating these survey pipelines using a set of "benchmark stars" in order to evaluate the accuracy and precision of the provided parameters and abundances is of utmost importance. The recent proposed set of Gaia FGK benchmark stars of Heiter et al. (2015) has no recommended stars within the critical metallicity range of $-2.0 <$ [Fe/H] $< -1.0$ dex. In this paper, we aim to add candidate Gaia benchmark stars inside of this metal-poor gap. We began with a sample of 21 metal-poor stars which was reduced to 10 stars by requiring accurate photometry and parallaxes, and high-resolution archival spectra. The procedure used to determine the stellar parameters was similar to Heiter et al. (2015) and Jofre et al. (2014) for consistency. The effective temperature (T$_{\mathrm{eff}}$) of all candidate stars was determined using the Infrared Flux Method utilizing multi-band photometry. The surface gravity (log g) was determined through fitting stellar evolutionary tracks. The [Fe/H] was determined using four different spectroscopic methods fixing the T$_{\mathrm{eff}}$ and log g from the values determined independent of spectroscopy. We discuss, star-by-star, the quality of each parameter including how it compares to literature, how it compares to a spectroscopic run where all parameters are free, and whether Fe I ionisation-excitation balance is achieved. From the 10 stars, we recommend a sample of five new metal-poor benchmark candidate stars which have consistent T$_{\mathrm{eff}}$ , log g, and [Fe/H] determined through several means. These stars can be used for calibration and validation purpose of stellar parameter and abundance pipelines and should be of highest priority for future interferometric studies., Comment: Accepted for publication in A&A, 18 Pages, 8 Figures, 7 Tables

The bibliographical compilation of stellar atmospheric parameters (Teff, logg, [Fe/H]) relying on high-resolution, high signal-to-noise spectroscopy started in the eighties with the so-called [Fe/H] catalogue, and was continued in 2010 with the PASTEL catalogue, which also includes determinations of Teff alone, based on various methods. Here we present an update of the PASTEL catalogue. The main journals and the CDS database have been surveyed to find relevant publications presenting new determinations of atmospheric parameters. As of February 2016, PASTEL includes 64082 determinations of either Teff or (Teff, logg, [Fe/H]) for 31401 stars, corresponding to 1142 bibliographical references. Some 11197 stars have a determination of the three parameters (Teff, logg, [Fe/H]) with a high-quality spectroscopic metallicity., Comment: 7 pages, accepted in A&A

In anticipation of the Gaia astrometric mission, a large sample of spectroscopic binaries has been observed since 2010 with the SOPHIE spectrograph at the Haute--Provence Observatory. Our aim is to derive the orbital elements of double-lined spectroscopic binaries (SB2s) with an accuracy sufficient to finally obtain the masses of the components with relative errors as small as 1 % when the astrometric measurements of Gaia are taken into account. In this paper we present the results from five years of observations of 10 SB2 systems with periods ranging from 37 to 881 days. Using the TODMOR algorithm we computed radial velocities from the spectra, and then derived the orbital elements of these binary systems. The minimum masses of the components are then obtained with an accuracy better than 1.2 % for the ten binaries. Combining the radial velocities with existing interferometric measurements, we derived the masses of the primary and secondary components of HIP 87895 with an accuracy of 0.98 % and 1.2 % respectively., Comment: 9 pages, 3 figures, 6 tables, Monthly Notices of the Royal Astronomical Society (2016)

Mass models of galactic disks traditionally rely on axisymmetric density and rotation curves, paradoxically acting as if their most remarkable asymmetric features, such as lopsidedness or spiral arms, were not important. In this article, we relax the axisymmetry approximation and introduce a methodology that derives 3D gravitational potentials of disk-like objects and robustly estimates the impacts of asymmetries on circular velocities in the disk midplane. Mass distribution models can then be directly fitted to asymmetric line-of-sight velocity fields. Applied to the grand-design spiral M99, the new strategy shows that circular velocities are highly nonuniform, particularly in the inner disk of the galaxy, as a natural response to the perturbed gravitational potential of luminous matter. A cuspy inner density profile of dark matter is found in M99, in the usual case where luminous and dark matter share the same center. The impact of the velocity nonuniformity is to make the inner profile less steep, although the density remains cuspy. On another hand, a model where the halo is core dominated and shifted by 2.2-2.5 kpc from the luminous mass center is more appropriate to explain most of the kinematical lopsidedness evidenced in the velocity field of M99. However, the gravitational potential of luminous baryons is not asymmetric enough to explain the kinematical lopsidedness of the innermost regions, irrespective of the density shape of dark matter. This discrepancy points out the necessity of an additional dynamical process in these regions: possibly a lopsided distribution of dark matter., Comment: Accepted for publication in Astronomy & Astrophysics, 20 pages, 17 figures. 2nd version after language editing

A large dataset of ~2800 spectra extracted from the ELODIE archive was analysed in order to find solar twins. A list of stellar spectra closely resembling the spectrum of the Sun was selected by applying a purely differential method, directly on the fluxes. As solar reference, 18 spectra of asteroids, Moon and blue sky were used. Atmospheric parameters and differential abundances of 8 chemical elements were determined for the solar twin candidates, after a careful selection of appropriate lines. The Li feature of the targets was investigated and additional information on absolute magnitude and age was gathered from the literature. HIP076114 (HD138573) is our best twin candidate, looking exactly like the Sun in all these properties., Comment: Accepted for publication in Astronomy & Astrophysics, 15 pages, 5 figures. All tables will be available on VizieR at CDS

In the fundamental quest of the rotation curve of the Milky Way, the tangent-point (TP) method has long been the simplest way to infer velocities for the inner, low latitude regions of the Galactic disk from observations of the gas component. We test the validity of the method on realistic gas distribution and kinematics of the Milky Way, using a numerical simulation of the Galaxy. We show that the resulting velocity profile strongly deviates from the true rotation curve of the simulation, as it overstimates it in the central regions, and underestimates it around the bar corotation. Also, its shape strongly depends on the orientation of the stellar bar. The discrepancies are caused by highly non-uniform azimuthal velocities, and the systematic selection by the TP method of high-velocity gas along the bar and spiral arms, or low-velocity gas in less dense regions. The velocity profile is in good agreement with the rotation curve only beyond corotation, far from massive asymmetric structures. Therefore the observed velocity profile of the Milky Way inferred by the TP method is expected to be very close to the true Galactic rotation curve for 4.5

In this article we summarise on-going work on the so-called Gaia FGK Benchmark Stars. This work consists of the determination of their atmospheric parameters and of the construction of a high-resolution spectral library. The definition of such a set of reference stars has become crucial in the current era of large spectroscopic surveys. Only with homogeneous and well documented stellar parameters can one exploit these surveys consistently and understand the structure and history of the Milky Way and therefore other of galaxies in the Universe., Comment: to appear in ASI Conference Series, 2014, Vol. 10 for the Workshop of Spectral Libraries held in Lyon, Oct. 2013

The stellar population models dramatically progressed with the arrival of large and complete libraries, ELODIE, CFLIB (=Indo-US) and MILES at a relatively high resolution. We show that the quality of the fits is not anymore limited by the size of the stellar libraries in a large range of ages (0.1 to 10 Gyrs) and metallicities (-2 to +0.4 dex). The main limitations of the empirical stellar libraries are (i) the coverage of the parameters space (lack of hot stars of low metallicity), (ii) the precision and homogeneity of the atmospheric parameters and (iii) the non-resolution of individual element abundances (in particular [$\alpha$/Fe]). Detailed abundance measurements in the large libraries, and usage of theoretical libraries are probably the next steps, and we show that a combination between an empirical (ELODIE) and a theoretical library (Coelho et al. 2005) immediately improves the modeling of ($\alpha$-enhanced) globular clusters., Comment: 4 pages; proceedings of IAU Symposium No. 241, "Stellar Populations as Building Blocks of Galaxies", editors A. Vazdekis and R. Peletier

We have compared simple stellar populations (SSPs) generated with different population synthesis tools: BC03, Vazdekis and Pegase.HR and different stellar libraries: ELODIE3.1, SteLib and MILES. We find that BC03/SteLib SSPs are biased toward solar metallicity, however Pegase.HR/ELODIE3.1 and Vazdekis/MILES are extremely consistent. The extensive coverage of the space of atmospheric parameters in the large stellar libraries allows precise synthesis for a large range of ages (0.1 .. 10 Gyr) and metallicities (-2 .. +0.4 dex) limited by the quality of the determination of stellar parameters (like temperature scale of the giants)., Comment: 2 pages; proceedings of IAU Symposium No. 241, "Stellar Populations as Building Blocks of Galaxies", editors A. Vazdekis and R. Peletier

We present the results of our investigation of three samples kinematically representative of the thin and thick disks and the Hercules stream using the catalogue of Soubiran & Girard (2005). We have observed abundance trends and age distribution of each component. Our results show that the two disks are chemically well separated, they overlap greatly in metallicity and both show parallel decreasing trends of alpha elements with increasing metallicity, in the interval -0.80 < [Fe/H] < -0.30. The thick disk is clearly older than the thin disk with a tentative evidence of an Age-Metallicity Relation over 2-3 Gyr and a hiatus in star formation before the formation of the thin disk. In order to improve the statistics on the disk's abundance trends, we have developed an automatic code, TGMET{\Large\alpha}; to determine (Teff, logg, [Fe/H], [\alpha/Fe]) for thousands of stellar spectra available in spectroscopic archives. We have assessed the performances of the algorithm for 350 spectra of stars being part of the abundance catalogue.

One way to extract more information from the integrated light of galaxies is to improve the spectral resolution at which observations and analysis are carried out. The population synthesis code currently providing the highest spectral resolution is Pegase-HR, which was made available by D. Le Borgne et al. in 2004. Based on an empirical stellar library, it provides synthetic spectra between 4000 and 6800 A at lambda/d(lambda)=10000 for any star formation history, with or without chemical evolution. Such a resolution is particularly useful for the study of low mass galaxies, massive star clusters, or other galaxy regions with low internal velocity dispersions. After a summary of the main features of Pegase-HR and comparisons with other population synthesis codes, this paper focuses on the inversion of optical galaxy spectra. We explore the limits of what information can or can not be recovered, based on theoretical principles and extensive simulations. First applications to extragalactic objects are shown., Comment: Inv. talk in "The Spectral Energy Distribution of Gas-Rich Galaxies: Confronting Models with Data", Heidelberg, 4-8 Oct. 2004, eds. C.C. Popescu and R.J. Tuffs, AIP Conf. Ser., in press

We test an automatic procedure to measure [Fe/H] and [alpha/Fe] on high resolution spectra. The test sample is the intersection of the ELODIE library and a catalogue of 830 stars having well determined abundances., Comment: Three-dimensional Universe with Gaia, 4-7 October 2004, Observatoire de Paris-Meudon, France (ESA SP-576), eds M. Perryman & C. Turon

We have investigated the abundance of several chemical elements in two large stellar samples kinematically representative of the thin and the thick disks of the Galaxy. Chemical, kinematical and age data have been collected from high quality sources in the literature. Velocities (U,V,W) have been computed and used to select stars with the highest probability to belong to the thin disk and the thick disk respectively. Our results show that the two disks are chemically well separated. Both exhibit a decline of [$\alpha$/Fe] with increasing [Fe/H]. A transition between the thin/thick disks stars is observed at 10 Gyr., Comment: To appear in Chemical Abundances and Mixing in Stars in the Milky Way Galaxy and its Satellites, ESO Astrophysics Symposia, ed. L. Pasquini & S. Randich (Springer-Verlag Press)

We present PEGASE-HR, a new stellar population synthesis program generating high resolution spectra (R=10 000) over the optical range lambda=400--680 nm. It links the spectro-photometric model of galaxy evolution PEGASE.2 (Fioc & Rocca-Volmerange 1997) to an updated version of the ELODIE library of stellar spectra observed with the 193 cm telescope at the Observatoire de Haute-Provence (Prugniel & Soubiran 2001a). The ELODIE star set gives a fairly complete coverage of the Hertzprung-Russell (HR) diagram and makes it possible to synthesize populations in the range [Fe/H]=-2 to +0.4. This code is an exceptional tool for exploring signatures of metallicity, age, and kinematics. We focus on a detailed study of the sensitivity to age and metallicity of the high-resolution stellar absorption lines and of the classical metallic indices proposed until now to solve the age-metallicity degeneracy. Validity tests on several stellar lines are performed by comparing our predictions for Lick indices to the models of other groups. The comparison with the lower resolution library BaSeL (Lejeune et al. 1997) confirms the quality of the ELODIE library when used for simple stellar populations (SSPs) from 10 Myr to 20 Gyr. Predictions for the evolved populations of globular clusters and elliptical galaxies are given and compared to observational data. Two new high-resolution indices are proposed around the Hgamma line. They should prove useful in the analysis of spectra from the new generation of telescopes and spectrographs., Comment: 18 pages, 18 figures. Astronomy & Astrophysics, in press. The models are available at http://www.iap.fr/pegase/

We present a database of 908 spectra of 709 stars obtained with the ELODIE spectrograph at Observatoire de Haute-Provence. 52 orders of the echelle spectra have been carefully fitted together to provide continuous, high-resolution spectra in the wavelength range 410 nm - 680 nm. The archive provides a large coverage of the space of atmospheric parameters : Teff from 3700 K to 13600 K, logg from 0.03 to 5.86 and [Fe/H] from -2.8 to +0.7. At the nominal resolution, R=42000, the mean signal-to-noise ratio is 150 per pixel. The spectra given at this resolution are normalized to their pseudo-continuum and are intended to serve for abundance studies, spectral classification and tests of stellar atmosphere models. A lower resolution version of the archive, at R=10000, is calibrated in physical flux with a broad-band photometric precision of 2.5% and narrow-band precision of 0.5%. It is scoped for stellar population synthesis of galaxies and clusters, and for kinematical investigations of stellar systems., Comment: 10 pages, accepted for publication in A&A, data available at http://www-obs.univ-lyon1.fr/hypercat/11/spectrophotometry.html