DSpace Angular :: Browsing by Author "Sbordone, L."

Browsing by Author "Sbordone, L."

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A new algorithm for optimizing the wavelength coverage for spectroscopic studies: Spectral Wavelength Optimization Code (SWOC)
(OXFORD UNIV PRESS, 2016) Ruchti, G. R.; Feltzing, S.; Lind, K.; Caffau, E.; Korn, A. J.; Schnurr, O.; Hansen, C. J.; Koch, A.; Sbordone, L.; de Jong, R. S.
The past decade and a half has seen the design and execution of several ground-based spectroscopic surveys, both Galactic and Extragalactic. Additionally, new surveys are being designed that extend the boundaries of current surveys. In this context, many important considerations must be done when designing a spectrograph for the future. Among these is the determination of the optimum wavelength coverage. In this work, we present a new code for determining the wavelength ranges that provide the optimal amount of information to achieve the required science goals for a given survey. In its first mode, it utilizes a user-defined list of spectral features to compute a figure-of-merit for different spectral configurations. The second mode utilizes a set of flux-calibrated spectra, determining the spectral regions that show the largest differences among the spectra. Our algorithm is easily adaptable for any set of science requirements and any spectrograph design. We apply the algorithm to several examples, including 4MOST, showing the method yields important design constraints to the wavelength regions.
Chemical abundances of giant stars in NGC 5053 and NGC 5634, two globular clusters associated with the Sagittarius dwarf spheroidal galaxy?
(EDP SCIENCES S A, 2015) Sbordone, L.; Monaco, L.; Moni Bidin, C.; Bonifacio, P.; Villanova, S.; Bellazzini, M.; Ibata, R.; Chiba, M.; Geisler, D.; Caffau, E.; Duffau, S.
Context. The tidal disruption of the Sagittarius dwarf spheroidal galaxy (Sgr dSph) is producing the most prominent substructure in the Milky Way (MW) halo, the Sagittarius Stream. Aside from field stars, it is suspected that the Sgr dSph has lost a number of globular clusters (GC). Many Galactic GC are thought to have originated in the Sgr dSph. While for some candidates an origin in the Sgr dSph has been confirmed owing to chemical similarities, others exist whose chemical composition has never been investigated.
Chemical abundances of giant stars in the Crater stellar system
(EDP SCIENCES S A, 2015) Bonifacio, P.; Caffau, E.; Zaggia, S.; Francois, P.; Sbordone, L.; Andrievsky, S. M.; Korotin, S. A.
Aims. We obtained spectra for two giants of Crater (Crater J113613-105227 and Crater J113615-105244) using X-Shooter at the VLT, with the purpose of determining their radial velocities and metallicities.
Chemical composition of a sample of bright solar-metallicity stars
(WILEY-V C H VERLAG GMBH, 2015) Caffau, E.; Mott, A.; Steffen, M.; Bonifacio, P.; Strassmeier, K. G.; Gallagher, A.; Faraggiana, R.; Sbordone, L.
We present a detailed analysis of seven young stars observed with the spectrograph SOPHIE at the Observatoire de Haute-Provence for which the chemical composition was incomplete or absent in the literature. For five stars, we derived the stellar parameters and chemical compositions using our automatic pipeline optimized for F, G, and K stars, while for the other two stars with high rotational velocity, we derived the stellar parameters by using other information (parallax), and performed a line-by-line analysis. Chromospheric emission-line fluxes from Ca II are obtained for all targets. The stellar parameters we derive are generally in good agreement with what is available in the literature. We provide a chemical analysis of two of the stars for the first time. The star HIP 80124 shows a strong Li feature at 670.8 nm implying a high lithium abundance. Its chemical pattern is not consistent with it being a solar sibling, as has been suggested. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Detailed abundances in stars belonging to ultra-faint dwarf spheroidal galaxies
(2012) François, P.; Monaco, L.; Villanova, S.; Catelan, Márcio; Bonifacio, P.; Bellazzini, M.; Moni Bidin, C.; Marconi, G.; Geisler, D.; Sbordone, L.
We report preliminary results concerning the detailed chemical composition of metal poor stars belonging to close ultra-faint dwarf galaxies (hereafter UfDSphs). The abundances have been determined thanks to spectra obtained with X-Shooter, a high efficiency spectrograph installed on one of the ESO VLT units. The sample of ultra-faint dwarf spheroidal stars have abundance ratios slightly lower to what is measured in field halo star of the same metallicity. We did not find extreme abundances in our Hercules stars as the one found by Koch for his 2 Hercules stars. The synthesis of the neutron capture elements Ba and Sr seems to originate from the same nucleosynthetic process in operation during the early stages of the galactic evolution....
Detailed chemical abundances of distant RR Lyrae stars in the Virgo Stellar Stream
(2016) Duffau, S.; Sbordone, L.; Vivas, A. K.; Hansen, C. J.; Zoccali, M.; Catelan, Márcio; Minniti, D.; Grebel, E. K.
We present the first detailed chemical abundances for distant RR Lyrae stars members of the Virgo Stellar Stream (VSS), derived from X- Shooter medium-resolution spectra. Sixteen elements from carbon to barium have been measured in six VSS RR Lyrae stars, sampling all main nucleosynthetic channels. For the first time we will be able to compare in detail the chemical evolution of the VSS progenitor with those of Local Group dwarf spheroidal galaxies (LG dSph) as well as the one of the smooth halo....
Galactic evolution of sulphur as traced by globular clusters
(EDP SCIENCES S A, 2015) Kacharov, N.; Koch, A.; Caffau, E.; Sbordone, L.
Context. Sulphur is an important volatile a element, but its role in the Galactic chemical evolution is still uncertain, and more observations constraining the sulphur abundance in stellar photospheres are required.
The chemical composition of red giants in 47 Tucanae II. Magnesium isotopes and pollution scenarios
(EDP SCIENCES S A, 2016) Thygesen, A. O.; Sbordone, L.; Ludwig, H. G.; Ventura, P.; Yong, D.; Collet, R.; Christlieb, N.; Melendez, J.; Zaggia, S.
Context. The phenomenon of multiple populations in globular clusters is still far from understood, with several proposed mechanisms to explain the observed behaviour. The study of elemental and isotopic abundance patterns are crucial for investigating the differences among candidate pollution mechanisms.
The Gaia-ESO Survey Mg-Al anti-correlation in iDR4 globular clusters
(EDP SCIENCES S A, 2017) Pancino, E.; Romano, D.; Tang, B.; Tautvaisiene, G.; Casey, A. R.; Gruyters, P.; Geisler, D.; San Roman, I.; Randich, S.; Alfaro, E. J.; Bragaglia, A.; Flaccomio, E.; Korn, A. J.; Recio Blanco, A.; Smiljanic, R.; Carraro, G.; Bayo, A.; Costado, M. T.; Damiani, F.; Jofre, P.; Lardo, C.; de laverny, P.; Monaco, L.; Morbidelli, L.; Sbordone, L.; Sousa, S. G.; Villanova, S.
We use Gaia-ESO (GES) Survey iDR4 data to explore the Mg-Alanti-correlation in globular clusters that were observed as calibrators, as a demonstration of the quality of Gaia-ESO Survey data and analysis. The results compare well with the available literature, within 0.1 dex or less, after a small (compared to the internal spreads) off set between the UVES and GIRAFFE data of 0.10-0.15 dex was taken into account. In particular, for the first time we present data for NGC 5927, which is one of the most metal-rich globular clusters studied in the literature so far with [Fe/H] = -0.39 +/- 0.04 dex; this cluster was included to connect with the open cluster regime in the Gaia-ESO Survey internal calibration. The extent and shape of the Mg-Al anti-correlation provide strong constraints on the multiple population phenomenon in globular clusters. In particular, we studied the dependency of the Mg-Al anti-correlation extension with metallicity, present-day mass, and age of the clusters, using GES data in combination with a large set of homogenized literature measurements. We find a dependency with both metallicity and mass, which is evident when fitting for the two parameters simultaneously, but we do not find significant dependency with age. We confirm that the Mg-Al anti-correlation is not seen in all clusters, but disappears for the less massive or most metal-rich clusters. We also use our data set to see whether a normal anti-correlation would explain the low [Mg/ff] observed in some extragalactic globular clusters, but find that none of the clusters in our sample can reproduce it; a more extreme chemical composition, such as that of NGC 2419, would be required. We conclude that GES iDR4 data already meet the requirements set by the main survey goals and can be used to study globular clusters in detail, even if the analysis procedures were not specifically designed for them.
The Gaia-ESO Survey: a quiescent Milky Way with no significant dark/stellar accreted disc(a similar to...)
(OXFORD UNIV PRESS, 2015) Ruchti, G. R.; Read, J. I.; Feltzing, S.; Serenelli, A. M.; McMillan, P.; Lind, K.; Bensby, T.; Bergemann, M.; Asplund, M.; Vallenari, A.; Flaccomio, E.; Pancino, E.; Korn, A. J.; Recio Blanco, A.; Bayo, A.; Carraro, G.; Costado, M. T.; Damiani, F.; Heiter, U.; Hourihane, A.; Jofre, P.; Kordopatis, G.; Lardo, C.; de Laverny, P.; Monaco, L.; Morbidelli, L.; Sbordone, L.; Worley, C. C.; Zaggia, S.
According to our current cosmological model, galaxies like the Milky Way are expected to experience many mergers over their lifetimes. The most massive of the merging galaxies will be dragged towards the disc plane, depositing stars and dark matter into an accreted disc structure. In this work, we utilize the chemodynamical template developed in Ruchti et al. to hunt for accreted stars. We apply the template to a sample of 4675 stars in the third internal data release from the Gaia-ESO Spectroscopic Survey. We find a significant component of accreted halo stars, but find no evidence of an accreted disc component. This suggests that the Milky Way has had a rather quiescent merger history since its disc formed some 8-10 billion years ago and therefore possesses no significant dark matter disc.
The Gaia-ESO Survey: Calibration strategy
(2017) Pancino, E.; Lardo, C.; Altavilla, G.; Marinoni, S.; Ragaini, S.; Cocozza, G.; Bellazzini, M.; Sabbi, E.; Zoccali, Manuela; Sbordone, L.
The Gaia-ESO Survey: Detailed abundances in the metal-poor globular cluster NGC 4372
(EDP SCIENCES S A, 2015) San Roman, I.; Munoz, C.; Geisler, D.; Villanova, S.; Kacharov, N.; Koch, A.; Carraro, G.; Tautvaisiene, G.; Vallenari, A.; Alfaro, E. J.; Bensby, T.; Flaccomio, E.; Francois, P.; Korn, A. J.; Pancino, E.; Recio Blanco, A.; Smiljanic, R.; Bergemann, M.; Costado, M. T.; Damiani, F.; Heiter, U.; Hourihane, A.; Jofre, P.; Lardo, C.; de Laverny, P.; Masseron, T.; Morbidelli, L.; Sbordone, L.; Sousa, S. G.; Worley, C. C.; Zaggia, S.
We present the abundance analysis for a sample of 7 red giant branch stars in the metal-poor globular cluster NGC 4372 based on UVES spectra acquired as part of the Gaia-ESO Survey. This is the first extensive study of this cluster from high-resolution spectroscopy. We derive abundances of O, Na, Mg, Al, Si, Ca, Sc, Ti, Fe, Cr, Ni, Y, Ba, and La. We find a metallicity of [Fe/H] = -2.19 +/- 0.03 and find no evidence of any metallicity spread. This metallicity makes NGC 4372 one of the most metal-poor Galactic globular clusters. We also find an a-enhancement typical of halo globular clusters at this metallicity. Significant spreads are observed in the abundances of light elements. In particular, we find a Na-O anticorrelation. Abundances of O are relatively high compared with other globular clusters. This could indicate that NGC 4372 was formed in an environment with high O for its metallicity. A Mg-Al spread is also present that spans a range of more than 0.5 dex in Al abundances. Na is correlated with Al and Mg abundances at a lower significance level. This pattern suggests that the Mg-Al burning cycle is active. This behavior can also be seen in giant stars of other massive, metal-poor clusters. A relation between light and heavy s-process elements has been identified.
The Gaia-ESO Survey: Empirical determination of the precision of stellar radial velocities and projected rotation velocities
(EDP SCIENCES S A, 2015) Jackson, R. J.; Jeffries, R. D.; Lewis, J.; Koposov, S. E.; Sacco, G. G.; Randich, S.; Gilmore, G.; Asplund, M.; Binney, J.; Bonifacio, P.; Drew, J. E.; Feltzing, S.; Ferguson, A. M. N.; Micela, G.; Neguerela, I.; Prusti, T.; Rix, H. W.; Vallenari, A.; Alfaro, E. J.; Prieto, C. Allende; Babusiaux, C.; Bensby, T.; Blomme, R.; Bragaglia, A.; Flaccomio, E.; Francois, P.; Hambly, N.; Irwin, M.; Korn, A. J.; Lanzafame, A. C.; Pancino, E.; Recio Blanco, A.; Smiljanic, R.; Van Eck, S.; Walton, N.; Bayo, A.; Bergemann, M.; Carraro, G.; Costado, M. T.; Damiani, F.; Edvardsson, B.; Franciosini, E.; Frasca, A.; Heiter, U.; Hill, V.; Hourihane, A.; Jofre, P.; Lardo, C.; de Laverny, P.; Lind, K.; Magrini, L.; Marconi, G.; Martayan, C.; Masseron, T.; Monaco, L.; Morbidelli, L.; Prisinzano, L.; Sbordone, L.; Sousa, S. G.; Worley, C. C.; Zaggia, S.
Context. The Gaia-ESO Survey (GES) is a large public spectroscopic survey at the European Southern Observatory Very Large Telescope.
The Gaia-ESO Survey: Extracting diffuse interstellar bands from cool star spectra DIB-based interstellar medium line-of-sight structures at the kpc scale
(EDP SCIENCES S A, 2015) Puspitarini, L.; Lallement, R.; Babusiaux, C.; Chen, H. C.; Bonifacio, P.; Sbordone, L.; Caffau, E.; Duffau, S.; Hill, V.; Monreal Ibero, A.; Royer, F.; Arenou, F.; Peralta, R.; Drew, J. E.; Bonito, R.; Lopez Santiago, J.; Alfaro, E. J.; Bensby, T.; Bragaglia, A.; Flaccomio, E.; Lanzafame, A. C.; Pancino, E.; Recio Blanco, A.; Smiljanic, R.; Costado, M. T.; Lardo, C.; de Laverny, P.; Zwitter, T.
Aims. We study how diffuse interstellar bands (DIBs) measured toward distance-distributed target stars can be used to locate dense interstellar (IS) clouds in the Galaxy and probe a line-of-sight (LOS) kinematical structure, a potentially useful tool when gaseous absorption lines are saturated or not available in the spectral range. Cool target stars are numerous enough for this purpose.
The Gaia-ESO Survey: Galactic evolution of sulphur and zinc
(EDP SCIENCES S A, 2017) Duffau, S.; Caffau, E.; Sbordone, L.; Bonifacio, P.; Andrievsky, S.; Korotin, S.; Babusiaux, C.; Salvadori, S.; Monaco, L.; Francois, P.; Skuladottir, A.; 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.; Jimenez Esteban, F. M.; Koch, A.; Magrini, L.; Pancino, E.; Tang, B.; Tautvaisiene, 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.; Damiani, F.; Franciosini, E.; Hourihane, A.; Jofre, P.; Lardo, C.; Lewis, J.; Morbidelli, L.; Sousa, S. G.; Worley, C. C.
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.
The Gaia-ESO Survey: radial distribution of abundances in the Galactic disc from open clusters and young-field stars
(EDP SCIENCES S A, 2017) Magrini, L.; Randich, S.; Kordopatis, G.; Prantzos, N.; Romano, D.; Ffi, A. Chie; Limongi, M.; Francois, P.; Pancino, E.; Friel, E.; Bragaglia, A.; Tautvaisiene, G.; Spina, L.; Overbeek, J.; Cantat Gaudin, T.; Donati, P.; Vallenari, A.; Sordo, R.; Jimenez Esteban, F. M.; Tang, B.; Drazdauskas, A.; Sousa, S.; Duffau, S.; Jofre, 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.
The Gaia-ESO Survey: revisiting the Li-rich giant problem
(OXFORD UNIV PRESS, 2016) 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.; Tautvaisiene, G.; Zaggia, S.; Zwitter, T.; Delgado Mena, E.; Chorniy, Y.; Martell, S. L.; Aguirre, V. Silva; 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.
The Gaia-ESO Survey: Sodium and aluminium abundances in giants and dwarfs Implications for stellar and Galactic chemical evolution
(EDP SCIENCES S A, 2016) Smiljanic, R.; Romano, D.; Bragaglia, A.; Donati, P.; Magrini, L.; Friel, E.; Jacobson, H.; Randich, S.; Ventura, P.; Lind, K.; Bergemann, M.; Nordlander, T.; Morel, T.; Pancino, E.; Tautvaisiene, G.; Adibekyan, V.; Tosi, M.; Vallenari, A.; Gilmore, G.; Bensby, T.; Francois, P.; Koposov, S.; Lanzafame, A. C.; Recio Blanco, A.; Bayo, A.; Carraro, G.; Casey, A. R.; Costado, M. T.; Franciosini, E.; Heiter, U.; Hill, V.; Hourihane, A.; Jofre, P.; Lardo, C.; de Laverny, P.; Lewis, J.; Monaco, L.; Morbidelli, L.; Sacco, G. G.; Sbordone, L.; Sousa, S. G.; Worley, C. C.; Zaggia, S.
Context. Stellar evolution models predict that internal mixing should cause some sodium overabundance at the surface of red giants more massive than similar to 1.5-2.0 M-circle dot. The surface aluminium abundance should not be affected. Nevertheless, observational results disagree about the presence and/or the degree of Na and Al overabundances. In addition, Galactic chemical evolution models adopting different stellar yields lead to very different predictions for the behavior of [Na/Fe] and [Al/Fe] versus [Fe/H]. Overall, the observed trends of these abundances with metallicity are not well reproduced.
The Gaia-ESO Survey: the selection function of the Milky Way field stars
(OXFORD UNIV PRESS, 2016) Stonkute, 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.; Tautvaisiene, G.; Casey, A. R.; Korn, A. J.; Lanzafame, A. C.; Pancino, E.; Franciosini, E.; Hourihane, A.; Jofre, 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.
The halo plus cluster system of the Galactic globular cluster NGC 1851(a similar to...)
(2014) Marino, A.F.; Milone, A.P.; Yong, D.; Dotter, A.; Da Costa, G.; Asplund, M.; Jerjen, H.; Cassisi, S.; Sbordone, L.; Angeloni, Rodolfo

Browsing by Author "Sbordone, L."

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