Examinando por Autor "Sacco G."
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Ítem The Gaia -ESO Survey: Open clusters in Gaia -DR1: A way forward to stellar age calibration(EDP Sciences, 2018-04) Randich S.; Tognelli E.; Jackson R.; Jeffries R.D.; Degl'Innocenti S.; Pancino E.; Fiorentin, P. Re; Spagna A.; Sacco G.; Bragaglia A.; Magrini L.; Moroni, P. G. Prada; Alfaro E.; Franciosini E.; Morbidelli L.; Roccatagliata V.; Bouy H.; Bravi L.; Jiménez-Esteban F.M.; Jordi C.; Zari E.l.; Tautvaišiene G.; Drazdauskas A.; Mikolaitis S.; Gilmore G.; Feltzing S.; Vallenari A.; Bensby T.; Koposov S.; Korn A.; Lanzafame A.; Smiljanic R.; Bayo A.; Carraro G.; Costado M.T.; Heiter U.; Hourihane A.; Jofré P.; Lewis J.; Monaco L.; Prisinzano L.; Sbordone L.; Sousa S.G.; Worley C.C.; Zaggia S.Context. Determination and calibration of the ages of stars, which heavily rely on stellar evolutionary models, are very challenging, while representing a crucial aspect in many astrophysical areas. Aims. We describe the methodologies that, taking advantage of Gaia-DR1 and the Gaia-ESO Survey data, enable the comparison of observed open star cluster sequences with stellar evolutionary models. The final, long-term goal is the exploitation of open clusters as age calibrators. Methods. We perform a homogeneous analysis of eight open clusters using the Gaia-DR1 TGAS catalogue for bright members and information from the Gaia-ESO Survey for fainter stars. Cluster membership probabilities for the Gaia-ESO Survey targets are derived based on several spectroscopic tracers. The Gaia-ESO Survey also provides the cluster chemical composition. We obtain cluster parallaxes using two methods. The first one relies on the astrometric selection of a sample of bona fide members, while the other one fits the parallax distribution of a larger sample of TGAS sources. Ages and reddening values are recovered through a Bayesian analysis using the 2MASS magnitudes and three sets of standard models. Lithium depletion boundary (LDB) ages are also determined using literature observations and the same models employed for the Bayesian analysis. Results. For all but one cluster, parallaxes derived by us agree with those presented in Gaia Collaboration (2017, A&A, 601, A19), while a discrepancy is found for NGC 2516; we provide evidence supporting our own determination. Inferred cluster ages are robust against models and are generally consistent with literature values. Conclusions. The systematic parallax errors inherent in the Gaia DR1 data presently limit the precision of our results. Nevertheless, we have been able to place these eight clusters onto the same age scale for the first time, with good agreement between isochronal and LDB ages where there is overlap. Our approach appears promising and demonstrates the potential of combining Gaia and ground-based spectroscopic datasets. © ESO 2018.Ítem The Gaia -ESO Survey: radial distribution of abundances in the Galactic disc from open clusters and young-field stars(EDP Sciences, 2017-07) Magrini L.; Randich S.; Kordopatis G.; Prantzos N.; Romano D.; Chieffi A.; Limongi M.; François P.; Pancino E.; Friel E.; Bragaglia A.; Tautvaišiene G.; Spina L.; Overbeek J.; Cantat-Gaudin T.; Donati P.; Vallenari A.; Sordo R.; Jiménez-Esteban F.M.; Tang B.; Drazdauskas A.; Sousa S.; Duffau S.; Jofré P.; Gilmore G.; Feltzing S.; Alfaro E.; Bensby T.; Flaccomio E.; Koposov S.; Lanzafame A.; Smiljanic R.; Bayo A.; Carraro G.; Casey A.R.; Costado M.T.; Damiani F.; Franciosini E.; Hourihane A.; Lardo C.; Lewis J.; Monaco L.; Morbidelli L.; Sacco G.; Sbordone L.; Worley C.C.; Zaggia S.Context. The spatial distribution of elemental abundances in the disc of our Galaxy gives insights both on its assembly process and subsequent evolution, and on the stellar nucleogenesis of the different elements. Gradients can be traced using several types of objects as, for instance, (young and old) stars, open clusters, HII regions, planetary nebulae. Aims. We aim to trace the radial distributions of abundances of elements produced through different nucleosynthetic channels - the α-elements O, Mg, Si, Ca and Ti, and the iron-peak elements Fe, Cr, Ni and Sc - by use of the Gaia-ESO IDR4 results for open clusters and young-field stars. Methods. From the UVES spectra of member stars, we have determined the average composition of clusters with ages > 0.1 Gyr. We derived statistical ages and distances of field stars. We traced the abundance gradients using the cluster and field populations and compared them with a chemo-dynamical Galactic evolutionary model. Results. The adopted chemo-dynamical model, with the new generation of metallicity-dependent stellar yields for massive stars, is able to reproduce the observed spatial distributions of abundance ratios, in particular the abundance ratios of [O/Fe] and [Mg/Fe] in the inner disc (5 kpcÍtem 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: The inner disk intermediate-age open cluster NGC 6802(EDP Sciences, 2017-05) Tang B.; Geisler D.; Friel E.; Villanova S.; Smiljanic R.; Casey A.R.; Randich S.; Magrini L.; San Roman I.; Muñoz C.; Cohen R.E.; Mauro F.; Bragaglia A.; Donati P.; Tautvaišiene G.; Drazdauskas A.; Ženoviene R.; Snaith O.; Sousa S.; Adibekyan V.; Costado M.T.; Blanco-Cuaresma S.; Jiménez-Esteban F.; Carraro G.; Zwitter T.; François P.; Jofrè P.; Sordo R.; Gilmore G.; Flaccomio E.; Koposov S.; Korn A.J.; Lanzafame A.C.; Pancino E.; Bayo A.; Damiani F.; Franciosini E.; Hourihane A.; Lardo C.; Lewis J.; Monaco L.; Morbidelli L.; Prisinzano L.; Sacco G.; Worley C.C.; Zaggia S.Milky Way open clusters are very diverse in terms of age, chemical composition, and kinematic properties. Intermediate-age and old open clusters are less common, and it is even harder to find them inside the solar Galactocentric radius, due to the high mortality rate and strong extinction inside this region. NGC 6802 is one of the inner disk open clusters (IOCs) observed by the Gaia-ESO survey (GES). This cluster is an important target for calibrating the abundances derived in the survey due to the kinematic and chemical homogeneity of the members in open clusters. Using the measurements from Gaia-ESO internal data release 4 (iDR4), we identify 95 main-sequence dwarfs as cluster members from the GIRAFFE target list, and eight giants as cluster members from the UVES target list. The dwarf cluster members have a median radial velocity of 13.6 ± 1.9 km s-1, while the giant cluster members have a median radial velocity of 12.0 ± 0.9 km s-1 and a median [Fe/H] of 0.10 ± 0.02 dex. The color-magnitude diagram of these cluster members suggests an age of 0.9 ± 0.1 Gyr, with (m-M)0 = 11.4 and E(B-V) = 0.86. We perform the first detailed chemical abundance analysis of NGC 6802, including 27 elemental species. To gain a more general picture about IOCs, the measurements of NGC 6802 are compared with those of other IOCs previously studied by GES, that is, NGC 4815, Trumpler 20, NGC 6705, and Berkeley 81. NGC 6802 shows similar C, N, Na, and Al abundances as other IOCs. These elements are compared with nucleosynthetic models as a function of cluster turn-off mass. The α, iron-peak, and neutron-capture elements are also explored in a self-consistent way. © ESO, 2017.Ítem The Gaia -ESO Survey: The N/O abundance ratio in the Milky Way?(EDP Sciences, 2018-10) Magrini L.; Vincenzo F.; Randich S.; Pancino E.; Casali G.; Tautvaišien G.; Drazdauskas A.; Mikolaitis S.; Minkevičiūt R.; Stonkut E.; Chorniy Y.; Bagdonas V.; Kordopatis G.; Friel E.; Roccatagliata V.; Jiménez-Esteban F.M.; Gilmore G.; Vallenari A.; Bensby T.; Bragaglia A.I.; Korn A.J.; Lanzafame A.C.; Smiljanic R.; Bayo A.; Casey A.R.; Costado M.T.; Franciosini E.; Jofré P.; Lewis J.; Mónaco L.; Morbidelli L.; Sacco G.; Worley C.; Hourihane A.Context. The abundance ratio N/O is a useful tool to study the interplay of galactic processes, for example star formation e ciency, timescale of infall, and outflow loading factor. Aims. We aim to trace log(N/O) versus [Fe/H] in the Milky Way and to compare this ratio with a set of chemical evolution models to understand the role of infall, outflow, and star formation e ciency in the building up of the Galactic disc. Methods. We used the abundances from IDR2-3, IDR4, IDR5 data releases of the Gaia-ESO Survey both for Galactic field and open cluster stars. We determined membership and average composition of open clusters and we separated thin and thick disc field stars. We considered the e ect of mixing in the abundance of N in giant stars. We computed a grid of chemical evolution models, suited to reproduce the main features of our Galaxy, exploring the e ects of the star formation e ciency, infall timescale, and di erential outflow. Results. With our samples, we map the metallicity range0:6 [Fe/H] 0.3 with a corresponding1:2 log(N/O) 0:2, where the secondary production of N dominates. Thanks to the wide range of Galactocentric distances covered by our samples, we can distinguish the behaviour of log(N/O) in di erent parts of the Galaxy. Conclusions. Our spatially resolved results allow us to distinguish di erences in the evolution of N/O with Galactocentric radius. Comparing the data with our models, we can characterise the radial regions of our Galaxy. A shorter infall timescale is needed in the inner regions, while the outer regions need a longer infall timescale, coupled with a higher star formation e ciency. We compare our results with nebular abundances obtained in MaNGA galaxies, finding in our Galaxy a much wider range of log(N/O) than in integrated observations of external galaxies of similar stellar mass, but similar to the ranges found in studies of individual H II regions. © ESO 2018.Ítem The Gaia -ESO Survey: The origin and evolution of s -process elements(EDP Sciences, 2018-09) Magrini L.; Spina L.; Randich S.; Friel E.; Kordopatis G.; Worley C.; Pancino E.; Bragaglia A.; Donati P.; Tautvaišienė G.; Bagdonas V.; Delgado-Mena E.; Adibekyan V.; Sousa S.G.; Jiménez-Esteban F.M.; Sanna N.; Roccatagliata V.; Bonito R.; Sbordone L.; Duffau S.; Gilmore G.; Feltzing S.; Jeffries R.D.; Vallenari A.; Alfaro E.J.; Bensby T.; Francois P.; Koposov S.; Korn A.J.; Recio-Blanco A.; Smiljanic R.; Bayo A.; Carraro G.; Casey A.R.; Costado M.T.; Damiani F.; Franciosini E.; Frasca A.; Hourihane A.; Jofré P.; De Laverny P.; Lewis J.; Masseron T.; Monaco L.; Morbidelli L.; Prisinzano L.; Sacco G.; Zaggia S.Context. Several works have found an increase of the abundances of the s-process neutron-capture elements in the youngest Galactic stellar populations. These trends provide important constraints on stellar and Galactic evolution and they need to be confirmed with large and statistically significant samples of stars spanning wide age and distance intervals. Aims. We aim to trace the abundance patterns and the time evolution of five s-process elements - two belonging to the first peak, Y and Zr, and three belonging to the second peak, Ba, La, and Ce - using the Gaia-ESO IDR5 results for open clusters and disc stars. Methods. From the UVES spectra of cluster member stars, we determined the average composition of clusters with ages >0.1 Gyr. We derived statistical ages and distances of field stars, and we separated them into thin and thick disc populations. We studied the time-evolution and dependence on metallicity of abundance ratios using open clusters and field stars whose parameters and abundances were derived in a homogeneous way. Results. Using our large and homogeneous sample of open clusters, thin and thick disc stars, spanning an age range larger than 10 Gyr, we confirm an increase towards young ages of s-process abundances in the solar neighbourhood. These trends are well defined for open clusters and stars located nearby the solar position and they may be explained by a late enrichment due to significant contribution to the production of these elements from long-living low-mass stars. At the same time, we find a strong dependence of the s-process abundance ratios on the Galactocentric distance and on the metallicity of the clusters and field stars. Conclusions. Our results, derived from the largest and most homogeneous sample of s-process abundances in the literature, confirm the growth with decreasing stellar ages of the s-process abundances in both field and open cluster stars. At the same time, taking advantage of the abundances of open clusters located in a wide Galactocentric range, these results offer a new perspective on the dependence of the s-process evolution on the metallicity and star formation history, pointing to different behaviours at various Galactocentric distances. © 2018 ESO.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: Matching chemodynamical simulations to observations of the Milky Way(Oxford University Press, 2018-01) Thompson B.B.; Few C.G.; Bergemann M.; Gibson B.K.; MacFarlane B.A.; Serenelli A.; Gilmore G.; Randich S.; Vallenari A.; Alfaro E.J.; Bensby T.I.; Francois P.; Korn A.J.; Bayo A.; Carraro G.; Casey A.R.; Costado M.T.; Donati P.; Franciosini E.; Frasca A.; Hourihane A.; Jofrè P.; Hill V.; Heiter U.; Koposov S.E.; Lanzafame A.; Lardo C.; de Laverny P.; Lewis J.; Magrini L.; Marconi G.; Masseron T.; Monaco L.; Morbidelli L.; Pancino E.; Prisinzano L.; Recio-Blanco A.; Sacco G.; Sousa S.G.; Tautvaišiene G.; Worley C.C.; Zaggia S.The typical methodology for comparing simulated galaxies with observational surveys is usually to apply a spatial selection to the simulation to mimic the region of interest covered by a comparable observational survey sample. In this work, we compare this approach with a more sophisticated post-processing in which the observational uncertainties and selection effects (photometric, surface gravity and effective temperature) are taken into account. We compare a 'solar neighbourhood analogue' region in a model MilkyWay-like galaxy simulated with RAMSES-CH with fourth release Gaia-ESO survey data. We find that a simple spatial cut alone is insufficient and that the observational uncertainties must be accounted for in the comparison. This is particularly true when the scale of uncertainty is large compared to the dynamic range of the data, e.g. in our comparison, the [Mg/Fe] distribution is affected much more than the more accurately determined [Fe/H] distribution. Despite clear differences in the underlying distributions of elemental abundances between simulation and observation, incorporating scatter to our simulation results to mimic observational uncertainty produces reasonable agreement. The quite complete nature of the Gaia-ESO survey means that the selection function has minimal impact on the distribution of observed age and metal abundances but this would become increasingly more important for surveys with narrower selection functions. © 2017 The Author(s).