Examinando por Autor "Worley, C. C."
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Ítem The Gaia-ESO Survey: Inhibited extra mixing in two giants of the open cluster Trumpler 20?(EDP SCIENCES, 2016-06) Smiljanic, R.; Franciosini, E.; Randich, S.; Magrini, L.; Bragaglia, A.; Pasquini, L.; Vallenari, A.; Tautvaišienė, G.; Biazzo, K.; Frasca, A.; Donati, P.; Delgado Mena, E.; Casey, A. R.; Geisler, D.; Villanova, S.; Tang, B.; Sousa, S. G.; Gilmore, G.; Bensby, T.; François, P.; Koposov, S. E.; Lanzafame, A. C.; Pancino, E.; Recio-Blanco, A.; Costado, M. T.; Hourihane, A.; Lardo, C.; de Laverny, P.; Lewis, J.; Monaco, L.; Morbidelli, L.; Sacco, G. G.; Worley, C. C.; Zaggia, S.; Martell, S.Aims. We report the discovery of two Li-rich giants, with A(Li) ~ 1.50, in an analysis of a sample of 40 giants of the open cluster Trumpler 20 (with turnoff mass ~1.8 M⊙). The cluster was observed in the context of the Gaia-ESO Survey. Methods. The atmospheric parameters and Li abundances were derived using high-resolution UVES spectra. The Li abundances were corrected for nonlocal thermodynamical equilibrium (non-LTE) effects. Results. Only upper limits of the Li abundance could be determined for the majority of the sample. Two giants with detected Li turned out to be Li rich: star MG 340 has A(Li)non−LTE = 1.54 ± 0.21 dex and star MG 591 has A(Li)non−LTE = 1.60 ± 0.21 dex. Star MG 340 is on average ~0.30 dex more rich in Li than stars of similar temperature, while for star MG 591 this difference is on average ~0.80 dex. Carbon and nitrogen abundances indicate that all stars in the sample have completed the first dredge-up. Conclusions. The Li abundances in this unique sample of 40 giants in one open cluster clearly show that extra mixing is the norm in this mass range. Giants with Li abundances in agreement with the predictions of standard models are the exception. To explain the two Li-rich giants, we suggest that all events of extra mixing have been inhibited. This includes rotation-induced mixing during the main sequence and the extra mixing at the red giant branch luminosity bump. Such inhibition has been suggested in the literature to occur because of fossil magnetic fields in red giants that are descendants of main-sequence Ap-type stars.Ítem The Gaia-ESO Survey: revisiting the Li-rich giant problem(OXFORD UNIV PRESS, 2016-07) Casey, A. R.; Ruchti, G.; Masseron, T.; Randich, S.; Gilmore, G.; Lind, K.; Kennedy, G. M.; Koposov, S. E.; Hourihane, A.; Franciosini, E.; Lewis, J. R.; Magrini, L.; Morbidelli, L.; Sacco, G. G.; Worley, C. C.; Feltzing, S.; Jeffries, R. D.; Vallenari, A.; Bensby, T.; Bragaglia, A.; Flaccomio, E.; Francois, P.; Korn, A. J.; Lanzafame, A.; Pancino, E.; Recio-Blanco, A.; Smiljanic, R.; Carraro, G.; Costado, M. T.; Damiani, F.; Donati, P.; Frasca, A.; Jofre, P.; Lardo, C.; de Laverny, P.; Monaco, L.; Prisinzano, L.; Sbordone, L.; Sousa, S. G.; Tautvaisien, G.; Zaggia, S.; Zwitter, T.; Delgado Mena, E.; Chorniy, Y.; Martell, S. L.; Silva Aguirre, V.; Miglio, A.; Chiappini, C.; Montalban, J.; Morel, T.; Valentini, M.The discovery of lithium-rich giants contradicts expectations from canonical stellar evolution. Here we report on the serendipitous discovery of 20 Li-rich giants observed during the Gaia-ESO Survey, which includes the first nine Li-rich giant stars known towards the CoRoT fields. Most of our Li-rich giants have near-solar metallicities and stellar parameters consistent with being before the luminosity bump. This is difficult to reconcile with deep mixing models proposed to explain lithium enrichment, because these models can only operate at later evolutionary stages: at or past the luminosity bump. In an effort to shed light on the Li-rich phenomenon, we highlight recent evidence of the tidal destruction of close-in hot Jupiters at the sub-giant phase. We note that when coupled with models of planet accretion, the observed destruction of hot Jupiters actually predicts the existence of Li-rich giant stars, and suggests that Li-rich stars should be found early on the giant branch and occur more frequently with increasing metallicity. A comprehensive review of all known Li-rich giant stars reveals that this scenario is consistent with the data. However, more evolved or metal-poor stars are less likely to host close-in giant planets, implying that their Li-rich origin requires an alternative explanation, likely related to mixing scenarios rather than external phenomena.Ítem The Gaia-ESO Survey: Separating disk chemical substructures with cluster models⋆ Evidence of a separate evolution in the metal-poor thin disk(EDP SCIENCES, 2016-02) Rojas-Arriagada, A.; Recio-Blanco, A.; de Laverny, P.; Schultheis, M.; Guiglion, G.; Mikolaitis, Š.; Kordopatis, G.; Hill, V.; Gilmore, G.; Randich, S.; Alfaro, E. J.; Bensby, T.; Koposov, S. E.; Costado, M. T.; Franciosini, E.; Hourihane, A.; Jofré, P.; Lardo, C.; Lewis, J.; Lind, K.; Magrini, L.; Monaco, L.; Morbidelli, L.; Sacco, G. G.; Worley, C. C.; Zaggia, S.; Chiappini, C.Context. Recent spectroscopic surveys have begun to explore the Galactic disk system on the basis of large data samples, with spatial distributions sampling regions well outside the solar neighborhood. In this way, they provide valuable information for testing spatial and temporal variations of disk structure kinematics and chemical evolution. Aims. The main purposes of this study are to demonstrate the usefulness of a rigorous mathematical approach to separate substructures of a stellar sample in the abundance-metallicity plane, and provide new evidence with which to characterize the nature of the metal-poor end of the thin disk sequence. Methods. We used a Gaussian mixture model algorithm to separate in the [Mg/Fe] vs. [Fe/H] plane a clean disk star subsample (essentially at R-GC < 10 kpc) from the Gaia-ESO survey (GES) internal data release 2 (iDR2). We aim at decomposing it into data groups highlighting number density and/or slope variations in the abundance-metallicity plane. An independent sample of disk red clump stars from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) was used to cross-check the identified features. Results. We find that the sample is separated into five groups associated with major Galactic components; the metal-rich end of the halo, the thick disk, and three subgroups for the thin disk sequence. This is confirmed with the sample of red clump stars from APOGEE. The three thin disk groups served to explore this sequence in more detail. The two metal-intermediate and metal-rich groups of the thin disk decomposition ([Fe/H] > 0 : 25 dex) highlight a change in the slope at solar metallicity. This holds true at different radial regions of the Milky Way. The distribution of Galactocentric radial distances of the metal-poor part of the thin disk ([Fe/H] < 0 : 25 dex) is shifted to larger distances than those of the more metal-rich parts. Moreover, the metal-poor part of the thin disk presents indications of a scale height intermediate between those of the thick and the rest of the thin disk, and it displays higher azimuthal velocities than the latter. These stars might have formed and evolved in parallel and/or dissociated from the inside-out formation taking place in the internal thin disk. Their enhancement levels might be due to their origin from gas pre-enriched by outflows from the thick disk or the inner halo. The smooth trends of their properties (their spatial distribution with respect to the plane, in particular) with [Fe/H] and [Mg/Fe] suggested by the data indicates a quiet dynamical evolution, with no relevant merger events.Ítem The Gaia-ESO Survey: the selection function of the Milky Way field stars(Royal Astronomical Society, 2016-04) Stonkutė, E.; Koposov, S. E.; Howes, L. M.; Feltzing, S.; Worley, C. C.; Gilmore, G.; Ruchti, G. R.; Kordopatis, G.; Randich, S.; Zwitter, T.; Bensby, T.; Bragaglia, A.; Smiljanic, R.; Costado, M. T.; Tautvaišienė, G.; Casey, A. R.; Korn, A. J.; Lanzafame, A. C.; Pancino, E.; Franciosini, E.; Hourihane, A.; Jofré, P.; Lardo, C.; Lewis, J.; Magrini, L.; Monaco, L.; Morbidelli, L.; Sacco, G. G.; Sbordone, L.The Gaia-ESO Survey was designed to target all major Galactic components (i.e. bulge, thin and thick discs, halo and clusters), with the goal of constraining the chemical and dynamical evolution of the Milky Way. This paper presents the methodology and considerations that drive the selection of the targeted, allocated and successfully observed Milky Way field stars. The detailed understanding of the survey construction, specifically the influence of target selection criteria on observed Milky Way field stars is required in order to analyse and interpret the survey data correctly. We present the target selection process for the Milky Way field stars observed with Very Large Telescope/Fibre Large Array Multi Element Spectrograph and provide the weights that characterize the survey target selection. The weights can be used to account for the selection effects in the Gaia-ESO Survey data for scientific studies. We provide a couple of simple examples to highlight the necessity of including such information in studies of the stellar populations in the Milky Way.