Suchergebnisse

Atomic diusion and mixing processes in stellar interiors influence the structure and the surface composition of stars. Some of these processes cannot yet be modelled from the first principles, and they require calibrations. This limits their applicability in stellar models used for studies of stellar populations and Galactic evolution. Aims. Our main goal is to put constraints on the stellar structure and evolution models using new refined measurements of the chemical composition in stars of a Galactic open cluster. Methods.We used medium-resolution, 19 200 R 21 500, optical spectra of stars in the open cluster NGC2420 obtained within the Gaia-ESO survey. The sample covers all evolutionary stages from the main sequence to the red giant branch. Stellar parameters were derived using a combined Bayesian analysis of spectra, 2MASS photometry, and astrometric data from Gaia DR2. The abundances of Mg, Ca, Fe, and Li were determined from non-local thermodynamic equilibrium (NLTE) synthetic spectra, which were computed using one-dimensional (1D) and averaged three-dimensional (3D) model atmospheres. We compare our results with a grid of Code d'Evolution Stellaire Adaptatif et Modulaire (CESTAM) stellar evolution models, which include atomic diusion, turbulent, and rotational mixing. Results. We find prominent evolutionary trends in the abundances of Fe, Ca, Mg, and Li with the mass of the stars in the cluster. Furthermore, Fe, Mg, and Ca show a depletion at the cluster turn-o, but the abundances gradually increase and flatten near the base of the red giant branch. The abundance trend for Li displays a signature of rotational mixing on the main sequence and abrupt depletion on the sub-giant branch, which is caused by advection of Li-poor material to the surface. The analysis of abundances combined with the CESTAM model predictions allows us to place limits on the parameter space of the models and to constrain the zone in the stellar interior, where turbulent mixing takes place. ; The work of E.S. was partially funded by the subsidy 3.9780.2017/8.9 allocated to Kazan Federal University for the state assignment in the sphere of scientific activities. MD acknowledges support by FCT/MCTES through national funds (PIDDAC) by these grants UIDB/04434/2020, UIDP/04434/2020 and PTDC/FIS-AST/30389/2017 and by FEDER – Fundo Europeu de Desenvolvimento Regional through COMPETE2020-Programa Operacional Competitividade e Internacionalização by this grant POCI-01-0145-FEDER-030389. MD is supported in the form of a work contract funded by national funds through Fundação para a Ciência e Tecnologia (FCT). M.D. acknowledges financial support from the "Programme National de Physique Stellaire" (PNPS) of the CNRS/INSU co-funded by the CEA and the CNES, France. We acknowledge support by the Collaborative Research centre SFB 881 (projects A5, A10), Heidelberg University, of the Deutsche Forschungsge-meinschaft (DFG, German Research Foundation). A.S. is partially supported by the grants ESP2017-82674-R (Spanish Government) and 2017-SGR-1131 (Gen-eralitat de Catalunya). TB was funded by the project grant "The New Milky Way" from the Knut and Alica Wallenberg Foundation, and project grant No. 2018-04857 from the Swedish Research Council. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www. cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/ consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. Based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 188.B-3002. These data products have been processed by the Cambridge Astronomy Survey Unit (CASU) at the Institute of Astronomy, University of Cambridge, and by the FLAMES/UVES reduction team at INAF/Osservatorio Astrofisico di Arcetri. These data have been obtained from the Gaia-ESO Survey Data Archive, prepared and hosted by the Wide Field Astronomy Unit, Institute for Astronomy, University of Edinburgh, which is funded by the UK Science and Technology Facilities Council. This work was partly supported by the European Union FP7 programme through ERC grant number 320360 and by the Leverhulme Trust through grant RPG-2012-541. We acknowledge the support from INAF and Ministero dell' Istruzione, dell' Università' e della Ricerca (MIUR) in the form of the grant "Premiale VLT 2012". The results presented here benefit from discussions held during the Gaia-ESO workshops and conferences supported by the ESF (European Science Foundation) through the GREAT Research Network Programme. We thank Jan Rybizki for a valuable input concerning the data representation. We thank Andreas Korn for a discussion on modelling the transport of elements. We thank an anonymous referee for their comments and suggestions.

Aims. We present a spectroscopic study of the dynamics of the ionized and neutral gas throughout the Lagoon nebula (M 8), using VLT-FLAMES data from the Gaia-ESO Survey. The new data permit exploration of the physical connections between the nebular gas and the stellar population of the associated star cluster NGC 6530. Methods. We characterized through spectral fitting emission lines of Hα, [N II] and [S II] doublets, [O III], and absorption lines of sodium D doublet, using data from the FLAMES-Giraffe and UVES spectrographs, on more than 1000 sightlines toward the entire face of the Lagoon nebula. Gas temperatures are derived from line-width comparisons, densities from the [S II] doublet ratio, and ionization parameter from Hα/[N II] ratio. Although doubly-peaked emission profiles are rarely found, line asymmetries often imply multiple velocity components along the same line of sight. This is especially true for the sodium absorption, and for the [O III] lines. Results. Spatial maps for density and ionization are derived, and compared to other known properties of the nebula and of its massive stars 9 Sgr, Herschel 36 and HD 165052 which are confirmed to provide most of the ionizing flux. The detailed velocity fields across the nebula show several expanding shells, related to the cluster NGC 6530, the O stars 9 Sgr and Herschel 36, and the massive protostar M 8East-IR. The origins of kinematical expansion and ionization of the NGC 6530 shell appear to be different. We are able to put constrains on the line-of-sight (relative or absolute) distances between some of these objects and the molecular cloud. The data show that the large obscuring band running through the middle of the nebula is being compressed by both sides, which might explain its enhanced density. We also find an unexplained large-scale velocity gradient across the entire nebula. At larger distances, the transition from ionized to neutral gas is studied using the sodium lines.© 2017 ESO. ; This work was partly supported by the European Union FP7 program through ERC grant number 320360 and by the Leverhulme Trust through grant RPG-2012-541. We acknowledge the support from INAF and Ministero dell' Istruzione, dell' Universita e della Ricerca (MIUR) in the form of the grant >Premiale VLT 2012>. T.Z. acknowledges support from the Slovenian Research Agency (research core funding No. P1-0188). F.J.-E. acknowledges financial support from the Spacetec-CM project (S2013/ICE-2822). M.T.C. acknowledges the financial support from the Spanish Ministerio de Economia y Competitividad, through grant AYA2016-75931-C2-1-P. The results presented here benefit from discussions held during the Gaia-ESO workshops and conferences supported by the ESF (European Science Foundation) through the GREAT Research Network Programme. ; Peer Reviewed

The Gaia-ESO Survey (GES) observed many open clusters as part of its programme to spectroscopically characterize the various Milky Way populations. GES spectroscopy and Gaia astrometry from its second data release are used here to assign membership probabilities to targets towards 32 open clusters with ages from 1 to 3800 Myr, based on maximum likelihood modelling of the 3D kinematics of the cluster and field populations. From a parent catalogue of 14 398 individual targets, 5032 stars with uniformly determined 3D velocities, Teff, log g, and chemistry are assigned cluster membership with probability >0.9, and with an average probability of 0.991. The robustness of the membership probabilities is demonstrated using independent membership criteria (lithium and parallax) in two of the youngest clusters. The addition of radial velocities improves membership discrimination over proper motion selection alone, especially in more distant clusters. The kinematically selected nature of the membership lists, independent of photometry and chemistry, makes the catalogue a valuable resource for testing stellar evolutionary models and investigating the time evolution of various parameters. ; This work was partly supported by the European Union FP7 programme through ERC grant number 320360 and by the Leverhulme Trust through grant no. RPG-2012-541. We acknowledge the support from INAF and Ministero dell' Istruzione, dell' Università' e della Ricerca (MIUR) in the form of the grant 'Premiale VLT 2012'. The results presented here benefit from discussions held during the Gaia-ESO workshops and conferences supported by the ESF (European Science Foundation) through the GREAT Research Network Programme. ; Peer reviewed

We take advantage of the Gaia-ESO Survey iDR4 bulge data to search for abundance anomalies that could shed light on the composite nature of the Milky Way bulge. The α-element (Mg, Si, and whenever available, Ca) abundances, and their trends with Fe abundances have been analysed for a total of 776 bulge stars. In addition, the aluminum abundances and their ratio to Fe and Mg have also been examined. Our analysis reveals the existence of low-α element abundance stars with respect to the standard bulge sequence in the [α/ Fe] versus [Fe/H] plane. Eighteen objects present deviations in [α/ Fe] ranging from 2.1 to 5.3σ with respect to the median standard value. Those stars do not show Mg-Al anti-correlation patterns. Incidentally, this sign of the existence of multiple stellar populations is reported firmly for the first time for the bulge globular cluster NGC 6522. The identified low-α abundance stars have chemical patterns that are compatible with those of the thin disc. Their link with massive dwarf galaxies accretion seems unlikely, as larger deviations in α abundance and Al would be expected. The vision of a bulge composite nature and a complex formation process is reinforced by our results. The approach used, which is a multi-method and model-driven analysis of high resolution data, seems crucial to reveal this complexity. © ESO, 2017. ; A.R.B., P.d.L., and V.H. acknowledge financial support form the ANR 14-CE33-014-01. This work was partly supported by the European Union FP7 programme through ERC grant number 320360 and by the Leverhulme Trust through grant RPG-2012-541. We acknowledge the support from INAF and Ministero dell'Istruzione, dell'Universita e della Ricerca (MIUR) in the form of the grant "Premiale VLT 2012". The results presented here benefit from discussions held during the Gaia-ESO workshops and conferences supported by the ESF (European Science Foundation) through the GREAT Research Network Programme. M. Zoccali gratefully acknowledge support by the Ministry of Economy, Development, and Tourism's Millenium Science Initiative through grant IC120009, awarded to the Millenium Institute of Astrophysics (MAS), by Fondecyt Regular 1150345 and by the BASAL-CATA Center for Astrophysics and Associated Technologies PFB-06.

Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S.Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC). ; Our nearest neighbor, Proxima Centauri, hosts a temperate terrestrial planet. We detected in radial velocities evidence of a possible second planet with minimum mass mc sin ic = 5.8 ± 1.9M⊕ and orbital period Pc = 5.21–0.22 +0.26 years. The analysis of photometric data and spectro-scopic activity diagnostics does not explain the signal in terms of a stellar activity cycle, but follow-up is required in the coming years for confirming its planetary origin. We show that the existence of the planet can be ascertained, and its true mass can be determined with high accuracy, by combining Gaia astrometry and radial velocities. Proxima c could become a prime target for follow-up and characterization with next-generation direct imaging instrumentation due to the large maximum angular separation of ~1 arc second from the parent star. The candidate planet represents a challenge for the models of super-Earth formation and evolution. Copyright © 2020 The Authors, some rights reserved. ; M.D. acknowledges financial support from Progetto Premiale 2015 FRONTIERA funding scheme of the Italian Ministry of Education, University, and Research. P.G. acknowledges financial support from the Italian Space Agency (ASI) under contract 2014-025-R.1.2015 to INAF. D.B. acknowledges financial support from INAF and Agenzia Spaziale Italiana (ASI grant no. 2014-025-R.1.2015) for the 2016 PhD fellowship programme of INAF. H.R.A.J. is supported by UK STFC grant ST/R006598/1. J.S.S. and P.A.P.R. acknowledge support by FONDECYT grant 1161218 and partial support from CONICYT project Basal AFB-170002. M.J.L.-G., N.M., C.R.-L., E.R., G.A., and J.F.G. acknowledge financial support from Spanish MINECO AYA2016-79425-C3-3-P, AYA2017-84390-C2-1-R (co-funded by FEDER), ESP2017-87143R, and ESP2017-87676-C05-02-R and the State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award for the Instituto de Astrofisica de Andalucia (SEV-2017-0709). G.A.-E. research is funded via grant ST/P000592/1 "Astronomy Research at Queen Mary"granted by the Science and Technology Facilities Council/United Kingdom. ; Peer reviewed

The combination of precise radial velocities from multi-object spectroscopy and highly accurate proper motions from Gaia DR2 opens up the possibility for detailed 3D kinematic studies of young star-forming regions and clusters. Here, we perform such an analysis by combining Gaia-ESO Survey spectroscopy with Gaia astrometry for ∼900 members of the Lagoon Nebula cluster, NGC 6530. We measure the 3D velocity dispersion of the region to be 5.35+0.39 -0.34 km s, which is large enough to suggest the region is gravitationally unbound. The velocity ellipsoid is anisotropic, implying that the region is not sufficiently dynamically evolved to achieve isotropy, though the central part of NGC 6530 does exhibit velocity isotropy that suggests sufficient mixing has occurred in this denser part. We find strong evidence that the stellar population is expanding, though this is preferentially occurring in the declination direction and there is very little evidence for expansion in the right ascension direction. This argues against a simple radial expansion pattern, as predicted by models of residual gas expulsion. We discuss these findings in the context of cluster formation, evolution, and disruption theories.© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. ; NJW acknowledges an STFC Ernest Rutherford Fellowship (grant number ST/M005569/1). RJP acknowledges support from the Royal Society in the form of a Dorothy Hodgkin Fellowship. AB acknowledges support from ICM (Iniciativa Cientifica Milenio) via the Nucleo Milenio de Formacion Planetaria. EJA acknowledges support from the Spanish Government Ministerio de Ciencia, Innovacion y Universidades though grant AYA2016-75 931-C2-1 and from the State Agency for Research of the Spanish MCIU through the 'Center of Excellence Severo Ochoa' award for the Instituto de Astrofisica de Andalucia (SEV-2017-0709). ; Peer Reviewed

Context. Reconstructing the structure and history of young clusters is pivotal to understanding the mechanisms and timescales of early stellar evolution and planet formation. Recent studies suggest that star clusters often exhibit a hierarchical structure, possibly resulting from several star formation episodes occurring sequentially rather than a monolithic cloud collapse. Aims. We aim to explore the structure of the open cluster and star-forming region NGC 2264 (∼3 Myr), which is one of the youngest, richest and most accessible star clusters in the local spiral arm of our Galaxy; we link the spatial distribution of cluster members to other stellar properties such as age and evolutionary stage to probe the star formation history within the region. Methods. We combined spectroscopic data obtained as part of the Gaia-ESO Survey (GES) with multi-wavelength photometric data from the Coordinated Synoptic Investigation of NGC 2264 (CSI 2264) campaign. We examined a sample of 655 cluster members, with masses between 0.2 and 1.8 M and including both disk-bearing and disk-free young stars. We used T estimates from GES and g,r,i photometry from CSI 2264 to derive individual extinction and stellar parameters. Results. We find a significant age spread of 4-5 Myr among cluster members. Disk-bearing objects are statistically associated with younger isochronal ages than disk-free sources. The cluster has a hierarchical structure, with two main blocks along its latitudinal extension. The northern half develops around the O-type binary star S Mon; the southern half, close to the tip of the Cone Nebula, contains the most embedded regions of NGC 2264, populated mainly by objects with disks and ongoing accretion. The median ages of objects at different locations within the cluster, and the spatial distribution of disked and non-disked sources, suggest that star formation began in the north of the cluster, over 5 Myr ago, and was ignited in its southern region a few Myr later. Star formation is likely still ongoing in the most embedded regions of the cluster, while the outer regions host a widespread population of more evolved objects; these may be the result of an earlier star formation episode followed by outward migration on timescales of a few Myr. We find a detectable lag between the typical age of disk-bearing objects and that of accreting objects in the inner regions of NGC 2264: the first tend to be older than the second, but younger than disk-free sources at similar locations within the cluster. This supports earlier findings that the characteristic timescales of disk accretion are shorter than those of disk dispersal, and smaller than the average age of NGC 2264 (i.e., ≲ 3 Myr). At the same time, we note that disks in the north of the cluster tend to be shorter-lived (∼2.5 Myr) than elsewhere; this may reflect the impact of massive stars within the region (notably S Mon), that trigger rapid disk dispersal. Conclusions. Our results, consistent with earlier studies on NGC 2264 and other young clusters, support the idea of a star formation process that takes place sequentially over a prolonged span in a given region. A complete understanding of the dynamics of formation and evolution of star clusters requires accurate astrometric and kinematic characterization of its population; significant advance in this field is foreseen in the upcoming years thanks to the ongoing Gaia mission, coupled with extensive ground-based surveys like GES.© ESO, 2017. ; This work is based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under program ID 188.B-3002. These data products have been processed by the Cambridge Astronomy Survey Unit (CASU) at the Institute of Astronomy, University of Cambridge, and by the FLAMES/UVES reduction team at INAF/Osservatorio Astrofisico di Arcetri. These data have been obtained from the Gaia-ESO Survey Data Archive, prepared and hosted by the Wide Field Astronomy Unit, Institute for Astronomy, University of Edinburgh, which is funded by the UK Science and Technology Facilities Council. This work is also based on observations made with the Spitzer Space Telescope, operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA, and on data from MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii. The authors acknowledge useful discussions with S. Sciortino. We also thank V. Kalari, A. Klutsch, and L. A. Hillen-brand for their comments on an earlier version of this manuscript. This work was partly supported by the European Union FP7 program through ERC grant number 320360 and by the Leverhulme Trust through grant RPG-2012-541. We acknowledge the support from INAF and Ministero dell'Istruzione, dell'Universita e della Ricerca (MIUR) in the form of the grant >Premiale VLT 2012>. The results presented here benefit from discussions held during the Gaia-ESO workshops and conferences supported by the ESF (European Science Foundation) through the GREAT Research Network program. The authors acknowledge support through the PRIN INAF 2014 funding scheme of the National Institute for Astrophysics (INAF) of the Italian Ministry of Education, University and Research (>The Gaia-ESO Survey>, P.I.: S. Randich). S.H.P.A. acknowledges financial support from CNPq, CAPES and Fapemig. M.T.C. acknowledges financial support from the Spanish Ministerio de Economia y Competitividad, through grant AYA2016-75931-C2-1-P.

Context. There have been conflicting results with respect to the extent that radial migration has played in the evolution of the Galaxy. Additionally, observations of the solar neighborhood have shown evidence of a merger in the past history of the Milky Way that drives enhanced radial migration. Aims. We attempt to determine the relative fraction of stars that have undergone significant radial migration by studying the orbital properties of metal-rich ([Fe/H] > 0.1) stars within 2 kpc of the Sun. We also aim to investigate the kinematic properties, such as velocity dispersion and orbital parameters, of stellar populations near the Sun as a function of [Mg/Fe] and [Fe/H], which could show evidence of a major merger in the past history of the Milky Way. Methods. We used a sample of more than 3000 stars selected from the fourth internal data release of the Gaia-ESO Survey. We used the stellar parameters from the Gaia-ESO Survey along with proper motions from PPMXL to determine distances, kinematics, and orbital properties for these stars to analyze the chemodynamic properties of stellar populations near the Sun. Results. Analyzing the kinematics of the most metal-rich stars ([Fe/H] > 0.1), we find that more than half have small eccentricities (e 7 kpc. We find that the highest [Mg/Fe], metal-poor populations have lower vertical and radial velocity dispersions compared to lower [Mg/Fe] populations of similar metallicity by ~10 km s. The median eccentricity increases linearly with [Mg/Fe] across all metallicities, while the perigalacticon decreases with increasing [Mg/Fe] for all metallicities. Finally, the most [Mg/Fe]-rich stars are found to have significant asymmetric drift and rotate more than 40 km s slower than stars with lower [Mg/Fe] ratios. Conclusions. While our results cannot constrain how far stars have migrated, we propose that migration processes are likely to have played an important role in the evolution of the Milky Way, with metal-rich stars migrating from the inner disk toward to solar neighborhood and past mergers potentially driving enhanced migration of older stellar populations in the disk.© ESO, 2018. ; The authors thank Ivan Minchev for a useful discussion and the anonymous referee for useful comments. M.R.H. and A.R.B. received financial support from ANR, reference 14-CE33-0014-01. S.F. and T.B. acknowledge support from the project grant >The New Milky Way> from the Knut and Alice Wallenberg Foundation. Based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under program ID 188.B-3002. These data products have been processed by the Cambridge Astronomy Survey Unit (CASU) at the Institute of Astronomy, University of Cambridge, and by the FLAMES/UVES reduction team at INAF/Osservatorio Astrofisico di Arcetri. These data have been obtained from the Gaia-ESO Survey Data Archive, prepared and hosted by the Wide Field Astronomy Unit, Institute for Astronomy, University of Edinburgh, which is funded by the UK Science and Technology Facilities Council. This work was partly supported by the European Union FP7 programme through ERC grant number 320360 and by the Leverhulme Trust through grant RPG-2012-541. We acknowledge the support from INAF and Ministero dell' Istruzione, dell' Universita' e della Ricerca (MIUR) in the form of the grant >Premiale VLT 2012>. The results presented here benefit from discussions held during the Gaia-ESO workshops and conferences supported by the ESF (European Science Foundation) through the GREAT Research Network Programme. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France and NASA's Astrophysics Data System.

Aims. We present observations from the Gaia-ESO Survey in the lines of Hα, [N II], [S II], and He I of nebular emission in the central part of the Carina nebula. Methods. We investigate the properties of the two already known kinematic components (approaching and receding), which account for the bulk of emission. Moreover, we investigate the features of the much less known low-intensity high-velocity (absolute RV >50 km s-1) gas emission. Results. We show that gas giving rise to Hα and He I emission is dynamically well correlated with but not identical to gas seen through forbidden-line emission. Gas temperatures are derived from line-width ratios, and densities from [S II] doublet ratios. The spatial variation of N ionization is also studied, and found to differ between the approaching and receding components. The main result is that the bulk of the emission lines in the central part of Carina arise from several distinct shell-like expanding regions, the most evident found around η Car, the Trumpler 14 core, and the star WR25. These "shells" are non-spherical and show distortions probably caused by collisions with other shells or colder, higher-density gas. Some of them are also partially obscured by foreground dust lanes, while very little dust is found in their interior. Preferential directions, parallel to the dark dust lanes, are found in the shell geometries and physical properties, probably related to strong density gradients in the studied region. We also find evidence that the ionizing flux emerging from η Car and the surrounding Homunculus nebula varies with polar angle. The high-velocity components in the wings of Hα are found to arise from expanding dust reflecting the η Car spectrum. ; This work was partly supported by the European Union FP7 programme through ERC grant number 320360 and by the Leverhulme Trust through grant RPG-2012-541.

Lithium abundance in most of the warm metal-poor main sequence stars shows a constarnt plateau (A(Li) ~ 2.2 dex) and then the upper envelope of the lithium vs. metallicity distribution increases as we approach solar metallicity. Meteorites, which carry information about the chemical composition of the interstellar medium (ISM) at the solar system formation time, show a lithium abundance A(Li) ~ 3.26 dex. This pattern reflects the Li enrichment history of the ISM during the Galaxy lifetime. After the initial Li production in big bang nucleosynthesis, the sources of the enrichment include asymptotic giant branch (AGB) stars, low-mass red giants, novae, type II supernovae, and Galactic cosmic rays. The total amount of enriched Li is sensitive to the relative contribution of these sources. Thus different Li enrichment histories are expected in the Galactic thick and thin disc. We investigate the main sequence stars observed with UVES in Gaia-ESO Survey iDR4 catalogue and find a Li-anticorrelation independent of [Fe/H], T, and log(g). Since in stellar evolution different α enhancements at the same metallicity do not lead to a measurable Li abundance change, the anticorrelation indicates that more Li is produced during the Galactic thin disc phase than during the Galactic thick disc phase. We also find a correlation between the abundance of Li and s-process elements Ba and Y, and they both decrease above the solar metallicity, which can be explained in the framework of the adopted Galactic chemical evolution models.© ESO 2018. ; This work is based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 188. B-3002 and 193. B-0936. These data products have been processed by the Cambridge Astronomy Survey Unit (CASU) at the Institute of Astronomy, University of Cambridge, and by the FLAMES/UVES reduction team at INAF/Osservatorio Astrofisico di Arcetri. Data used her were obtained from the Gaia-ESO Survey Data Archive, prepared and hosted by the Wide Field Astronomy Unit, Institute for Astronomy, University of Edinburgh, which is funded by the UK Science and Technology Facilities Council. This work was partly supported by the European Union FP7 programme through ERC grant number 320360 and by the Leverhulme Trust through grant RPG-2012-541. We acknowledge the support from INAF and Ministero dell' Istruzione, dell' Universita' e della Ricerca (MIUR) in the form of the grant >Premiale VLT 2012>. The results presented here benefit from discussions held during the Gaia-ESO workshops and conferences supported by the ESF (European Science Foundation) through the GREAT Research Network Programme. This research has made use of the TOPCAT catalogue handling and plotting tool (Taylor 2005, 2017); of the Simbad database and the VizieR catalogue access tool, CDS, Strasbourg, France (Ochsenbein et al. 2000); and of NASA's Astrophysics Data System. X. F acknowledges helpful discussions with Nikos Prantzos and Paolo Molaro, and thanks Zhiyu Zhang for the help on MCMC calculations. E. D. M. and S. G. S. acknowledge the support from Fundacao para a Ciencia e a Tecnologia (FCT) through national funds and from FEDER through COMPETE2020 by the following grants: UID/FIS/04434/2013 & POCI-01-0145-FEDER-007672, PTDC/FIS-AST/1526/2014 & POCI-01-0145-FEDER-016886, and PTDC/FIS-AST/7073/2014 & POCI-01-0145-FEDER-016880. E. D. M. and S. G. S. also acknowledge the support from FCT through Investigador FCT contracts IF/00849/2015/CP1273/CT003 and IF/00028/2014/CP1215/CT0002. C. A. acknowledges to the Spanish grant AYA2015-63588-P within the European Founds for Regional Development (FEDER). A. K. and T. B. acknowledge the project grant >The New Milky Way> from the Knut and Alice Wallenberg Foundation. R. S. acknowledges support from the Polish Ministry of Science and Higher Education.

Context. In very young clusters, stellar age distribution is empirical proof of the duration of star cluster formation and thus it gives indications of the physical mechanisms involved in the star formation process. Determining the amount of interstellar extinction and the correct reddening law are crucial steps to derive fundamental stellar parameters and in particular accurate ages from the Hertzsprung-Russell diagram. Aims. In this context, we seek to derive accurate stellar ages for NGC 6530, the young cluster associated with the Lagoon Nebula to infer the star formation history of this region. Methods. We used the Gaia-ESO survey observations of the Lagoon Nebula, together with photometric literature data and Gaia DR2 kinematics, to derive cluster membership and fundamental stellar parameters. Using spectroscopic effective temperatures, we analysed the reddening properties of all objects and derived accurate stellar ages for cluster members. Results. We identified 652 confirmed and 9 probable members. The reddening inferred for members and non-members allows us to distinguish foreground objects, mainly main-sequence stars, and background objects, mainly giants, and to trace the three-dimensional structure of the nebula. This classification is in agreement with the distances inferred from Gaia DR2 parallaxes for these objects. Finally, we derive stellar ages for 382 confirmed cluster members for which we obtained the individual reddening values. In addition, we find that the gravity-sensitive γ index distribution for the M-type stars is correlated with stellar age. Conclusions. For all members with Teff The Gaia-ESO Survey>, P.I.: S. Randich). This work was partly supported by the European Union FP7 programme through ERC grant number 320360 and by the Leverhulme Trust through grant RPG-2012-541. ; Peer Reviewed

Context. Pismis 18 is a moderately populated, intermediate-Age open cluster located within the solar circle at a Galactocentric distance of about seven kpc. Few open clusters have been studied in detail in the inner disc region before the Gaia-ESO Survey. Aims. New data from the Gaia-ESO Survey allowed us to conduct an extended radial velocity membership study as well as spectroscopic metallicity and detailed chemical abundance measurements for this cluster. Methods. Gaia-ESO Survey data for 142 potential members, lying on the upper main sequence and on the red clump, yielded radial velocity measurements, which, together with proper motion measurements from the Gaia Second Data Release (Gaia DR2), were used to determine the systemic velocity of the cluster and membership of individual stars. Photometry from Gaia DR2 was used to re-determine cluster parameters based on high confidence member stars only. Cluster abundance measurements of six radial-velocity member stars with UVES high-resolution spectroscopy are presented for 23 elements. Results. The average radial velocity of 26 high confidence members is-27.5 ± 2.5 (std) km s with an average proper motion of pmra =-5.65 ± 0.08 (std) mas yr and pmdec =-2.29 ± 0.11 (std) mas yr. According to the new estimates, based on high confidence members, Pismis 18 has an age of τ = 700 Myr, interstellar reddening of E(B-V) = 0.562 mag and a de-reddened distance modulus of DM = 11.96 mag. The median metallicity of the cluster (using the six UVES stars) is [Fe/H] = +0.23 ± 0.05 dex, with [α/Fe] = 0.07 ± 0.13 and a slight enhancement of s-and r-neutron-capture elements. Conclusions. With the present work, we fully characterized the open cluster Pismis 18. We confirmed its present location in the inner disc. We estimated a younger age than the previous literature values and we gave, for the first time, its metallicity and its detailed abundances. Its [α/Fe] and [s-process/Fe], both slightly super-solar, are in agreement with other inner-disc open clusters observed by the Gaia-ESO survey.© ESO 2019. ; Based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 188.B-3002. These data products have been processed by the Cambridge Astronomy Survey Unit (CASU) at the Institute of Astronomy, University of Cambridge, and by the FLAMES/UVES reduction team at INAF/Osservatorio Astrofisico di Arcetri. These data have been obtained from the Gaia-ESO Survey Data Archive, prepared and hosted by the Wide Field Astronomy Unit, Institute for Astronomy, University of Edinburgh, which is funded by the UK Science and Technology Facilities Council. This work was partly supported by the European Union FP7 programme through ERC grant number 320360 and by the Leverhulme Trust through grant RPG-2012-541. We acknowledge the support from INAF and Ministero dell' Istruzione, dell' Universita' e della Ricerca (MIUR) in the form of the grant >Premiale VLT 2012>. The results presented here benefit from discussions held during the Gaia-ESO workshops and conferences supported by the ESF (European Science Foundation) through the GREAT Research Network Programme. The research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7-SPACE-2013-1) under grant agreement no. 606740. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. E. T. acknowledges the University of Pisa (Low and intermediate mass stellar models for the age determination of stellar clusters observed by the Gaia satellite, PI: S. Degl'Innocenti) and INFN (Iniziativa specifica TAsP). A. R. C. acknowledges support through the Australian Research Council through grant DP160100637. E. D. -M. acknowledges the support from Fundacao para a Ciencia e a Tecnologia (FCT) through national funds and from FEDER through COMPETE2020 by the following grants UID/FIS/04434/2013 & POCI-01-0145-FEDER-007672, PTDC/FIS-AST/7073/2014 & POCI-01-0145-FEDER-016880 and by the Investigador FCT contract IF/00849/2015. S. F. was supported by the project grant >The New Milky Way> from Knut and Alice Wallenberg Foundation. R. S. acknowledges support from the Polish Ministry of Science and Higher Education. A. B. acknowledges PREMIALE 2015 MITiC (PI B. Garilli). ; Peer Reviewed

Aims: We present the first extensive spectroscopic study of the global population in star clusters Trumpler 16, Trumpler 14, and Collinder 232 in the Carina nebula, using data from the Gaia-ESO Survey, down to solar-mass stars. Methods: In addition to the standard homogeneous survey data reduction, a special processing was applied here because of the bright nebulosity surrounding Carina stars. Results: We find about 400 good candidate members ranging from OB types down to slightly subsolar masses. About 100 heavily reddened early-type Carina members found here were previously unrecognized or poorly classified, including two candidate O stars and several candidate Herbig Ae/Be stars. Their large brightness makes them useful tracers of the obscured Carina population. The spectroscopically derived temperatures for nearly 300 low-mass members enables the inference of individual extinction values and the study of the relative placement of stars along the line of sight. Conclusions: We find a complex spatial structure with definite clustering of low-mass members around the most massive stars and spatially variable extinction. By combining the new data with existing X-ray data, we obtain a more complete picture of the three-dimensional spatial structure of the Carina clusters and of their connection to bright and dark nebulosity and UV sources. The identification of tens of background giants also enables us to determine the total optical depth of the Carina nebula along many sightlines. We are also able to put constraints on the star formation history of the region with Trumpler 14 stars found to be systematically younger than stars in other subclusters. We find a large percentage of fast-rotating stars among Carina solar-mass members, which provide new constraints on the rotational evolution of pre-main-sequence stars in this mass range.© 2017 ESO. ; This work was partly supported by the European Union FP7 program through ERC grant number 320360 and by the Leverhulme Trust through grant RPG-2012-541. ; Peer Reviewed

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 ≲ 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 (τ < 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, Ti » I, Ti » II, Na » I, Mg » I, Al » I, Si » I, 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. ; With funding from the Spanish government through the "María de Maeztu Unit of Excellence" accreditation (MDM-2017-0737)