Examinando por Autor "Drazdauskas A."
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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: 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: 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: 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.