Examinando por Autor "Sousa S.G."
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Ítem SWEET-Cat updated: New homogenous spectroscopic parameters(EDP Sciences, 2018-12) Sousa S.G.; Adibekyan V.; Delgado-Mena E.; Santos N.C.; Andreasen D.T.; Ferreira A.C.S.; Tsantaki M.; Barros S.C.C.; Demangeon O.; Israelian G.; Faria J.P.; Figueira P.; Mortier A.; Brandão I.; Montalto M.; Rojas-Ayala B.; Santerne A.Context. Exoplanets have now been proven to be very common. The number of its detections continues to grow following the development of better instruments and missions. One key step for the understanding of these worlds is their characterization, which mostly depend on their host stars. Aims. We perform a significant update of the Stars With ExoplanETs CATalog (SWEET-Cat), a unique compilation of precise stellar parameters for planet-host stars provided for the exoplanet community. Methods. We made use of high-resolution spectra for planet-host stars, either observed by our team or found in several public archives. The new spectroscopic parameters were derived for the spectra following the same homogeneous process (ARES+MOOG). The host star parameters were then merged together with the planet properties listed in exoplanet.eu to perform simple data analysis. Results. We present new spectroscopic homogeneous parameters for 106 planet-host stars. Sixty-three planet hosts are also reviewed with new parameters. We also show that there is a good agreement between stellar parameters derived for the same star but using spectra obtained from different spectrographs. The planet-metallicity correlation is reviewed showing that the metallicity distribution of stars hosting low-mass planets (below 30 M is indistinguishable from that from the solar neighborhood sample in terms of metallicity distribution. © ESO 2018.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: 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: 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: Evidence of atomic diffusion in M67?(Oxford University Press, 2018-07) Bertelli Motta C.; Pasquali A.; Richer J.; Michaud G.; Salaris M.; Bragaglia A.; Magrini L.; Randich S.; Grebel E.K.; Adibekyan V.; Blanco-Cuaresma S.; Drazdauskas A.; Fu X.; Martell S.; Tautvaišiene G.; Gilmore G.; Alfaro E.J.; Bensby T.; 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.; Franciosini E.; Heiter U.; Hourihane A.; Jofré P.; Lardo C.; Lewis J.; Monaco L.; Morbidelli L.; Sousa S.G.; Worley C.C.; Zaggia S.; Sacco, G.G.Investigating the chemical homogeneity of stars born from the same molecular cloud at virtually the same time is very important for our understanding of the chemical enrichment of the interstellar medium and with it the chemical evolution of the Galaxy. One major cause of inhomogeneities in the abundances of open clusters is stellar evolution of the cluster members. In this work, we investigate variations in the surface chemical composition of member stars of the old open clusterM67 as a possible consequence of atomic diffusion effects taking place during the main-sequence phase. The abundances used are obtained from high-resolution UVES/FLAMES spectra within the framework of the Gaia-ESO Survey. We find that the surface abundances of stars on the main sequence decrease with increasing mass reaching a minimum at the turn-off. After deepening of the convective envelope in subgiant branch stars, the initial surface abundances are restored.We found themeasured abundances to be consistent with the predictions of stellar evolutionary models for a cluster with the age and metallicity of M67. Our findings indicate that atomic diffusion poses a non-negligible constraint on the achievable precision of chemical tagging methods. © 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.Ítem The Gaia-ESO Survey: Galactic evolution of sulphur and zinc(EDP Sciences, 2017-08) Duffau S.; Caffau E.; Babusiaux C.; Damiani F.; Franciosini E.; Jofré P.; Sbordone L.; Salvadori S.; Hourihane A.; Lardo C.; Lewis J.; Morbidelli L.; Sousa S.G.; Worley C.C.; Bonifacio P.; Andrievsky S.; Korotin S.; Monaco L.; François P.; Skúladóttir Á.; Bragaglia A.; Donati P.; Spina L.; Gallagher A.J.; Ludwig H.-G.; Christlieb N.; Hansen C.J.; Mott A.; Steffen M.; Zaggia S.; Blanco-Cuaresma S.; Calura F.; Friel E.; Jiménez-Esteban F.M.; Koch A.; Magrini L.; Pancino E.; Tang B.; Tautvaišiene G.; Vallenari A.; Hawkins K.; Gilmore G.; Randich S.; Feltzing S.; Bensby T.; Flaccomio E.; Smiljanic R.; Bayo A.; Carraro G.; Casey A.R.; Costado M.T.Context. Due to their volatile nature, when sulphur and zinc are observed in external galaxies, their determined abundances represent the gas-phase abundances in the interstellar medium. This implies that they can be used as tracers of the chemical enrichment of matter in the Universe at high redshift. Comparable observations in stars are more difficult and, until recently, plagued by small number statistics. Aims. We wish to exploit the Gaia-ESO Survey (GES) data to study the behaviour of sulphur and zinc abundances of a large number of Galactic stars, in a homogeneous way. Methods. By using the UVES spectra of the GES sample, we are able to assemble a sample of 1301 Galactic stars, including stars in open and globular clusters in which both sulphur and zinc were measured. Results. We confirm the results from the literature that sulphur behaves as an α-element. We find a large scatter in [Zn/Fe] ratios among giant stars around solar metallicity. The lower ratios are observed in giant stars at Galactocentric distances less than 7.5 kpc. No such effect is observed among dwarf stars, since they do not extend to that radius. Conclusions. Given the sample selection, giants and dwarfs are observed at different Galactic locations, and it is plausible, and compatible with simple calculations, that Zn-poor giants trace a younger population more polluted by SN Ia yields. It is necessary to extend observations in order to observe both giants and dwarfs at the same Galactic location. Further theoretical work on the evolution of zinc is also necessary. © 2017 ESO.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).Ítem The Gaia-ESO Survey: Structural and dynamical properties of the young cluster Chamaeleon i(EDP Sciences, 2017-05) Sacco G.G.; Spina L.; Randich S.; Palla F.; Parker R.J.; Jeffries R.D.; Jackson R.; Meyer M.R.; Mapelli M.; Lanzafame A.C.; Bonito R.; Damiani F.; Franciosini E.; Frasca A.; Klutsch A.; Prisinzano L.; Tognelli E.; Degl'Innocenti S.; Prada Moroni P.G.; Alfaro E.J.; Micela G.; Prusti T.; Barrado D.; Biazzo K.; Bouy H.; Bravi L.; Lopez-Santiago J.; Wright N.J.; Bayo A.; Gilmore G.; Bragaglia A.; Flaccomio E.; Koposov S.E.; Pancino E.; Casey A.R.; Costado M.T.; Donati P.; Hourihane A.; Jofré P.; Lardo C.; Lewis J.; Magrini L.; Monaco L.; Morbidelli L.; Sousa S.G.; Worley C.C.; Zaggia S.Investigating the physical mechanisms driving the dynamical evolution of young star clusters is fundamental to our understanding of the star formation process and the properties of the Galactic field stars. The young (~2 Myr) and partially embedded cluster Chamaeleon I is one of the closest laboratories for the study of the early stages of star cluster dynamics in a low-density environment. The aim of this work is to study the structural and kinematical properties of this cluster combining parameters from the high-resolution spectroscopic observations of the Gaia-ESO Survey with data from the literature. Our main result is the evidence of a large discrepancy between the velocity dispersion (σstars = 1.14 ± 0.35 km s-1) of the stellar population and the dispersion of the pre-stellar cores (~0.3 km s-1) derived from submillimeter observations. The origin of this discrepancy, which has been observed in other young star clusters, is not clear. It has been suggested that it may be due to either the effect of the magnetic field on the protostars and the filaments or to the dynamical evolution of stars driven by two-body interactions. Furthermore, the analysis of the kinematic properties of the stellar population puts in evidence a significant velocity shift (~1 km s-1) between the two subclusters located around the north and south main clouds of the cluster. This result further supports a scenario where clusters form from the evolution of multiple substructures rather than from a monolithic collapse. Using three independent spectroscopic indicators (the gravity indicator γ, the equivalent width of the Li line at 6708 Å, and the Hα 10% width), we performed a new membership selection. We found six new cluster members all located in the outer region of the cluster, proving that Chamaeleon I is probably more extended than previously thought. Starting from the positions and masses of the cluster members, we derived the level of substructure Q, the surface density Σ, and the level of mass segregation ΛMSR of the cluster. The comparison between these structural properties and the results of N-body simulations suggests that the cluster formed in a low-density environment, in virial equilibrium or a supervirial state, and highly substructured. © 2017 ESO.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.