Examinando por Autor "Duffau S."
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Ítem Discovery of a thin stellar stream in the SLAMS survey(Oxford University Press, 2018) Jethwa P.; Torrealba G.; Navarrete C.; Carballo-Bello J.A.; de Boer T.; Erkal D.; Koposov S.E.; Duffau S.; Geisler D.; Catelan M.; Belokurov V.We report the discovery of a thin stellar stream - which we name the Jet stream - crossing the constellations of Hydra and Pyxis. The discovery was made in data from the Search for the Leading Arm of Magellanic Satellites (SLAMS) survey, which comprises deep g and r imaging for a 650 deg2 region above the Galactic disc performed by the CTIO Blanco + DECam. SLAMS photometric catalogues have been made publicly available. The stream is approximately 0.18 deg wide and 10 deg long, though it is truncated by the survey footprint. Its colour-magnitude diagram is consistent with an old, metal-poor stellar population at a heliocentric distance of approximately 29 kpc. We corroborate thismeasurement by identifying a spatially coincident overdensity of likely blue horizontal branch stars at the same distance. There is no obvious candidate for a surviving stream progenitor. © 2018 The Author(s).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 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.Ítem The globular cluster NGC7492 and the Sagittarius tidal stream: Together but unmixed(Oxford University Press, 2018-03) Carballo-Bello J.A.; Corral-Santana J.M.; Catelan M.; Martínez-Delgado D.; Muñoz R.R.; Sollima A.; Navarrete C.; Duffau S.; Côté P.; Mora M.D.We have derived from VIMOS spectroscopy the radial velocities for a sample of 71 stars selected from CFHT/Megacam photometry around the Galactic globular cluster NGC7492. In the resulting velocity distribution, it is possible to distinguish two relevant non-Galactic kinematic components along the same line of sight: a group of stars at 〈vr〉~125 km s-1 which is compatible with the velocity of the old leading arm of the Sagittarius tidal stream, and a larger number of objects at 〈 vr〉 ~ -110 km s-1 that might be identified as members of the trailing wrap of the same stream. The systemic velocity of NGC7492 set at vr ~-177 km s-1 differs significantly from that of both components, thus our results confirm that this cluster is not one of the globular clusters deposited by the Sagittarius dwarf spheroidal in the Galactic halo, even if it is immersed in the stream. A group of stars with 〈 vr〉 ~ - 180 km s-1 might be comprised of cluster members along one of the tidal tails of NGC7492. © 2017 The Author(s).