Examinando por Autor "Friel E."
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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: 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: 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.