Examinando por Autor "Klutsch A."
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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: Lithium depletion in the Gamma Velorum cluster and inflated radii in low-mass pre-main-sequence stars(Oxford University Press, 2017-01) Jeffries R.D.; Jackson R.J.; Franciosini E.; Randich S.; Barrado D.; Frasca A.; Klutsch A.; Lanzafame A.C.; Prisinzano L.; Sacco G.G.; Gilmore G.; Vallenari A.; Alfaro E.J.; Koposov S.E.; Pancino E.; Bayo A.; Casey A.R.; Costado M.T.; Damiani F.; Hourihane A.; Lewis J.; Jofre P.; Magrini L.; Monaco L.; Morbidelli L.; Worley C.C.; Zaggia S.; Zwitter T.We show that non-magnetic models for the evolution of pre-main-sequence (PMS) stars cannot simultaneously describe the colour-magnitude diagram (CMD) and the pattern of lithium depletion seen in the cluster of young, low-mass stars surrounding γ 2 Velorum. The age of 7.5 ± 1 Myr inferred from the CMD is much younger than that implied by the strong Li depletion seen in the cluster M-dwarfs, and the Li depletion occurs at much redder colours than predicted. The epoch at which a star of a given mass depletes its Li and the surface temperature of that star are both dependent on its radius. We demonstrate that if the low-mass stars have radii ~10 per cent larger at a given mass and age, then both the CMD and the Li-depletion pattern of the Gamma Velorum cluster are explained at a common age of ≃ 18- 21 Myr. This radius inflation could be produced by some combination of magnetic suppression of convection and extensive cool starspots. Models that incorporate radius inflation suggest that PMS stars, similar to those in the Gamma Velorum cluster, in the range 0.2 < M/M ⊙ < 0.7, are at least a factor of 2 older and ~7 per cent cooler than previously thought and that their masses are much larger (by > 30 per cent) than inferred from conventional, non-magnetic models in the Hertzsprung-Russell diagram. Systematic changes of this size may be of great importance in understanding the evolution of young stars, disc lifetimes and the formation of planetary systems. © 2016 The Authors.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.