Examinando por Autor "Lind K."
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Ítem Atomic data for the Gaia-ESO Survey(EDP Sciences, 2021-01-01) Heiter U.; Lind K.; Bergemann M.; Asplund M.; Mikolaitis Š.; Barklem P. S.; Masseron T.; De Laverny P.; Magrini L.; Edvardsson B.; Jönsson H.; Pickering J. C.; Ryde N.; Bayo Arán A.; Bensby T.; Casey A. R.; Feltzing S.; Jofré P.; Korn A. J.; Pancino E.; Damiani F.; Lanzafame A.; Lardo C.; Monaco L.; Morbidelli L.; Smiljanic R.; Worley C.; Zaggia S.; Randich S.; Gilmore G.F.Context. We describe the atomic and molecular data that were used for the abundance analyses of FGK-type stars carried out within the Gaia-ESO Public Spectroscopic Survey in the years 2012 to 2019. The Gaia-ESO Survey is one among several current and future stellar spectroscopic surveys producing abundances for Milky-Way stars on an industrial scale. Aims. We present an unprecedented effort to create a homogeneous common line list, which was used by several abundance analysis groups using different radiative transfer codes to calculate synthetic spectra and equivalent widths. The atomic data are accompanied by quality indicators and detailed references to the sources. The atomic and molecular data are made publicly available at the CDS. Methods. In general, experimental transition probabilities were preferred but theoretical values were also used. Astrophysical gf-values were avoided due to the model-dependence of such a procedure. For elements whose lines are significantly affected by a hyperfine structure or isotopic splitting, a concerted effort has been made to collate the necessary data for the individual line components. Synthetic stellar spectra calculated for the Sun and Arcturus were used to assess the blending properties of the lines. We also performed adetailed investigation of available data for line broadening due to collisions with neutral hydrogen atoms. Results. Among a subset of over 1300 lines of 35 elements in the wavelength ranges from 475 to 685 nm and from 850 to 895 nm, we identified about 200 lines of 24 species which have accurate gf-values and are free of blends in the spectra of the Sun and Arcturus. For the broadening due to collisions with neutral hydrogen, we recommend data based on Anstee-Barklem-O'Mara theory, where possible. We recommend avoiding lines of neutral species for which these are not available. Theoretical broadening data by R.L. Kurucz should be used for Sc II, Ti II, and Y II lines; additionally, for ionised rare-earth species, the Unsöld approximation with an enhancement factor of 1.5 for the line width can be used. Conclusions. The line list has proven to be a useful tool for abundance determinations based on the spectra obtained within the Gaia-ESO Survey, as well as other spectroscopic projects. Accuracies below 0.2 dex are regularly achieved, where part of the uncertainties are due to differences in the employed analysis methods. Desirable improvements in atomic data were identified for a number of species, most importantly Al I, S I, and Cr II, but also Na I, Si I, Ca II, and Ni I.Ítem The Gaia -ESO Survey: Exploring the complex nature and origins of the Galactic bulge populations(EDP Sciences, 2017-05) Rojas-Arriagada A.; Recio-Blanco A.; De Laverny P.; Mikolaitis Š.; Matteucci F.; Spitoni E.; Schultheis M.; Hayden M.; Hill V.; Zoccali M.; Minniti D.; Gonzalez O.A.; Gilmore G.; Randich S.; Feltzing S.; Alfaro E.J.; Babusiaux C.; Bensby T.; Bragaglia A.; Flaccomio E.; Koposov S.E.; Pancino E.; Bayo A.; Carraro G.; Casey A.R.; Costado M.T.; Damiani F.; Donati P.; Franciosini E.; Hourihane A.; Jofré P.; Lardo C.; Lewis J.; Lind K.; Magrini L.; Morbidelli L.; Sacco G.G.; Worley C.C.; Zaggia S.Context. As observational evidence steadily accumulates, the nature of the Galactic bulge has proven to be rather complex: the structural, kinematic, and chemical analyses often lead to contradictory conclusions. The nature of the metal-rich bulge - and especially of the metal-poor bulge - and their relation with other Galactic components, still need to be firmly defined on the basis of statistically significant high-quality data samples. Aims. We used the fourth internal data release of the Gaia-ESO survey to characterize the bulge metallicity distribution function (MDF), magnesium abundance, spatial distribution, and correlation of these properties with kinematics. Moreover, the homogeneous sampling of the different Galactic populations provided by the Gaia-ESO survey allowed us to perform a comparison between the bulge, thin disk, and thick disk sequences in the [Mg/Fe] vs. [Fe/H] plane in order to constrain the extent of their eventual chemical similarities. Methods. We obtained spectroscopic data for ∼2500 red clump stars in 11 bulge fields, sampling the area -10° ≥ l ≥ +8° and -10° ≥ b ≥ -4° from the fourth internal data release of the Gaia-ESO survey. A sample of ∼6300 disk stars was also selected for comparison. Spectrophotometric distances computed via isochrone fitting allowed us to define a sample of stars likely located in the bulge region. Results. From a Gaussian mixture models (GMM) analysis, the bulge MDF is confirmed to be bimodal across the whole sampled area. The relative ratio between the two modes of the MDF changes as a function of b, with metal-poor stars dominating at high latitudes. The metal-rich stars exhibit bar-like kinematics and display a bimodality in their magnitude distribution, a feature which is tightly associated with the X-shape bulge. They overlap with the metal-rich end of the thin disk sequence in the [Mg/Fe] vs. [Fe/H] plane. On the other hand, metal-poor bulge stars have a more isotropic hot kinematics and do not participate in the X-shape bulge. Their Mg enhancement level and general shape in the [Mg/Fe] vs. [Fe/H] plane is comparable to that of the thick disk sequence. The position at which [Mg/Fe] starts to decrease with [Fe/H], called the "knee", is observed in the metal-poor bulge at [Fe/H]knee = -0:37 ± 0:09, being 0.06 dex higher than that of the thick disk. Although this difference is inside the error bars, it suggest a higher star formation rate (SFR) for the bulge than for the thick disk. We estimate an upper limit for this difference of Δ[Fe/H]knee = 0:24 dex. Finally, we present a chemical evolution model that suitably fits the whole bulge sequence by assuming a fast (<1 Gyr) intense burst of stellar formation that takes place at early epochs. Conclusions.We associate metal-rich stars with the bar boxy/peanut bulge formed as the product of secular evolution of the early thin disk. On the other hand, the metal-poor subpopulation might be the product of an early prompt dissipative collapse dominated by massive stars. Nevertheless, our results do not allow us to firmly rule out the possibility that these stars come from the secular evolution of the early thick disk. This is the first time that an analysis of the bulge MDF and α-abundances has been performed in a large area on the basis of a homogeneous, fully spectroscopic analysis of high-resolution, high S/N data. © ESO 2017.Ítem The Gaia -ESO Survey: Lithium enrichment histories of the Galactic thick and thin disc(EDP Sciences, 2018-02) Fu X.; Romano D.; Bragaglia A.; Mucciarelli A.; Lind K.; Delgado Mena E.; Sousa S.G.; Randich S.; Bressan A.; Sbordone L.; Martell S.; Korn A.J.; Abia C.; Smiljanic R.; Jofré P.; Pancino E.; Tautvaišiene G.; Tang B.; Magrini L.; Lanzafame A.C.; Carraro G.; Bensby T.; Damiani F.; Alfaro E.J.; Flaccomio E.; Morbidelli L.; Zaggia S.; Lardo C.; Monaco L.; Frasca A.; Donati P.; Drazdauskas A.; Chorniy Y.; Bayo A.; Kordopatis G.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], Teff, 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.Ítem The Gaia -ESO Survey: Spectroscopic-asteroseismic analysis of K2 stars in Gaia -ESO(EDP Sciences, 2020-11) Worley C.C.; Jofré P.; Rendle B.; Miglio A.; Magrini L.; Feuillet D.; Gavel A.; Smiljanic R.; Lind K.; Korn A.; Gilmore G.; Randich S.; Hourihane A.; Gonneau A.; Francois P.; Lewis J.; Sacco G.; Bragaglia A.; Heiter U.; Feltzing S.; Bensby T.; Irwin M.; Gonzalez Solares E.; Murphy D.; Bayo A.; Sbordone L.; Zwitter T.; Lanzafame A.C.; Walton N.; Zaggia S.; Alfaro E.J.; Morbidelli L.; Sousa S.; Monaco L.; Carraro G.; Lardo C.Context. The extensive stellar spectroscopic datasets that are available for studies in Galactic Archeaology thanks to, for example, the Gaia-ESO Survey, now benefit from having a significant number of targets that overlap with asteroseismology projects such as Kepler, K2, and CoRoT. Combining the measurements from spectroscopy and asteroseismology allows us to attain greater accuracy with regard to the stellar parameters needed to characterise the stellar populations of the Milky Way. Aims. The aim of this Gaia-ESO Survey special project is to produce a catalogue of self-consistent stellar parameters by combining measurements from high-resolution spectroscopy and precision asteroseismology. Methods. We carried out an iterative analysis of 90 K2@Gaia-ESO red giants. The spectroscopic values of Teff were used as input in the seismic analysis to obtain log g values. The seismic estimates of log were then used to re-determine the spectroscopic values of Teff and [Fe/H]. Only one iteration was required to obtain parameters that are in good agreement for both methods and, thus, to obtain the final stellar parameters. A detailed analysis of outliers was carried out to ensure a robust determination of the parameters. The results were then combined with Gaia DR2 data to compare the seismic log with a parallax-based log and to investigate instances of variations in the velocity and possible binaries within the dataset. Results. This analysis produced a high-quality catalogue of stellar parameters for 90 red giant stars from K2@Gaia-ESO that were determined through iterations between spectroscopy and asteroseismology. We compared the seismic gravities with those based on Gaia parallaxes to find an offset which is similar to other studies that have used asteroseismology. Our catalogue also includes spectroscopic chemical abundances and radial velocities, as well as indicators for possible binary detections. © ESO 2020.Ítem The Gaia-ESO Survey: Churning through the Milky Way(EDP Sciences, 2018-01) Hayden M.R.; Recio-Blanco A.; De Laverny P.; Mikolaitis S.; Guiglion G.; Randich S.; Bayo A.; Bensby T.; Bergemann M.; Bragaglia A.; Casey A.; Costado M.; Feltzing S.; Franciosini E.; Hourihane A.; Jofre P.; Koposov S.; Kordopatis G.; Lanzafame A.; Lardo C.; Lewis J.; Lind K.; Magrini L.; Monaco L.; Morbidelli L.; Pancino E.; Sacco G.; Stonkute E.; Worley C.C.; Zwitter T.; Hill V.; Gilmore G.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< 0.2) or are on nearly circular orbits. Slightly more than 20% of the metal-rich stars have perigalacticons Rp> 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-1. 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-1 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.Ítem The Gaia-ESO Survey: The present-day radial metallicity distribution of the Galactic disc probed by pre-main-sequence clusters(EDP Sciences, 2017-05) Spina L.; Randich S.; Magrini L.; Jeffries R.D.; Friel E.D.; Sacco G.G.; Pancino E.; Bonito R.; Bravi L.; Franciosini E.; Klutsch A.; Montes D.; Gilmore G.; Vallenari A.; Bensby T.; Bragaglia A.; Flaccomio E.; Koposov S.E.; Korn A.J.; Lanzafame A.C.; Smiljanic R.; Bayo A.; Carraro G.; Casey A.R.; Costado M.T.; Damiani F.; Donati P.; Frasca A.; Hourihane A.; Jofré P.; Lewis J.; Lind K.; Monaco L.; Morbidelli L.; Prisinzano L.; Sousa S.G.; Worley C.C.; Zaggia S. lContext. The radial metallicity distribution in the Galactic thin disc represents a crucial constraint for modelling disc formation and evolution. Open star clusters allow us to derive both the radial metallicity distribution and its evolution over time. Aims. In this paper we perform the first investigation of the present-day radial metallicity distribution based on [Fe/H] determinations in late type members of pre-main-sequence clusters. Because of their youth, these clusters are therefore essential for tracing the current interstellar medium metallicity. Methods. We used the products of the Gaia-ESO Survey analysis of 12 young regions (age < 100 Myr), covering Galactocentric distances from 6.67 to 8.70 kpc. For the first time, we derived the metal content of star forming regions farther than 500 pc from the Sun. Median metallicities were determined through samples of reliable cluster members. For ten clusters the membership analysis is discussed in the present paper, while for other two clusters (i.e. Chamaeleon I and Gamma Velorum) we adopted the members identified in our previous works. Results. All the pre-main-sequence clusters considered in this paper have close-To-solar or slightly sub-solar metallicities. The radial metallicity distribution traced by these clusters is almost flat, with the innermost star forming regions having [Fe/H] values that are 0.10-0.15 dex lower than the majority of the older clusters located at similar Galactocentric radii. Conclusions. This homogeneous study of the present-day radial metallicity distribution in the Galactic thin disc favours models that predict a flattening of the radial gradient over time. On the other hand, the decrease of the average [Fe/H] at young ages is not easily explained by the models. Our results reveal a complex interplay of several processes (e.g. star formation activity, initial mass function, supernova yields, gas flows) that controlled the recent evolution of the Milky Way. © ESO, 2017.