Examinando por Autor "Bonito R."
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Ítem The Gaia -ESO Survey: Calibrating the lithium-age relation with open clusters and associations: I. Cluster age range and initial membership selections(EDP Sciences, 2020-11) Albarrán M.L.G.; Montes D.; Garrido M.G.; Tabernero H.M.; Hernández J.I.G.; Marfil E.; Frasca A.; Lanzafame A.C.; Klutsch A.; Franciosini E.; Randich S.; Smiljanic R.; Korn A.J.; Gilmore G.; Alfaro E.J.; Baratella M.; Bayo A.; Bensby T.; Bonito R.; Carraro G.; Delgado Mena E.; Feltzing S.; Gonneau A.; Heiter U.; Hourihane A.; Esteban F.J.; Jofre P.; Masseron T.; Monaco L.; Morbidelli L.; Prisinzano L.; Roccatagliata V.; Sousa S.; Van Der Swaelmen M.; Worley C.C.; Zaggia S.Context. Previous studies of open clusters have shown that lithium depletion is not only strongly age dependent but also shows a complex pattern with other parameters that is not yet understood. For pre- and main-sequence late-type stars, these parameters include metallicity, mixing mechanisms, convection structure, rotation, and magnetic activity. Aims. We perform a thorough membership analysis for a large number of stars observed within the Gaia-ESO survey (GES) in the field of 20 open clusters, ranging in age from young clusters and associations, to intermediate-age and old open clusters. Methods. Based on the parameters derived from the GES spectroscopic observations, we obtained lists of candidate members for each of the clusters in the sample by deriving radial velocity distributions and studying the position of the kinematic selections in the EW(Li)-versus-Teff plane to obtain lithium members. We used gravity indicators to discard field contaminants and studied [Fe/H] metallicity to further confirm the membership of the candidates. We also made use of studies using recent data from the Gaia DR1 and DR2 releases to assess our member selections. Results. We identified likely member candidates for the sample of 20 clusters observed in GES (iDR4) with UVES and GIRAFFE, and conducted a comparative study that allowed us to characterize the properties of these members as well as identify field contaminant stars, both lithium-rich giants and non-giant outliers. Conclusions. This work is the first step towards the calibration of the lithium-age relation and its dependence on other GES parameters. During this project we aim to use this relation to infer the ages of GES field stars, and identify their potential membership to young associations and stellar kinematic groups of different ages. © ESO 2020.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: 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.