Examinando por Autor "Sbordone, Luca"

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    Ítem
    Detailed investigation of two high-speed evolved Galactic stars
    (John Wiley and Sons Inc, 2022-03) Matas Pinto, Aroa del Mar; Caffau, Elisabetta; François, Patrick; Spite, Monique; Bonifacio, Piercarlo; Wanajo, Shinya; Aoki, Wako; Monaco, Lorenzo; Suda, Takuma; Spite, François; Sbordone, Luca; Lombardo, Linda; Mucciarelli, Alessio
    The study of metal poor stars provides clarification and knowledge about the primordial Universe. Specially, halo stars provide explanations of the nature of the first generations of stars and the nucleosynthesis in the metal-poor regime. We present a detailed chemical analysis and determination of the kinematic and orbital properties of two stars characterized by high speed with respect to the Sun. We analyzed two high-resolution Subaru spectra employing the MyGIsFOS code, which allows to derive the detailed chemical abundances for 28 elements (C, N, O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, and Eu), and abundance from two ionization states in the case of four elements (Ti, Cr, Fe, and Zr). TYC 622–742–1 and TYC 1193–1918–1 are metal-poor stars ([Fe/H] of −2.37 and −1.60), they are similar in the chemical pattern with respect to Fe, they are (Formula presented.) enhanced and show a slight excess in Eu abundance. Both giant stars are poor in C and rich in N, as expected for evolved stars, and this fact is supported by the low (Formula presented.) isotopic ratio in TYC 1193–1918–1. Nevertheless, the C abundance of TYC 622–742–1 is particularly low. TYC 622–742–1 and TYC 1193–1918–1 have a similar chemical composition to the other Galactic halo stars of comparable metallicity. According to their kinematics, both stars belong to the Galactic halo, but they are not a part of the Gaia-Sausage-Enceladus structure. © 2021 Wiley-VCH GmbH
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    Extra-tidal star candidates in globular clusters of the sagittarius dwarf spheroidal galaxy
    (EDP Sciences, 2022-09) Kundu, Richa; Navarrete, Camila; Sbordone, Luca; Carballo-Bello, Julio A.; Fernández-Trincado, José G.; Minniti, Dante; Singh, Harinder P.
    Context. Globular clusters (GCs) associated with the Sagittarius dwarf spheroidal galaxy (Sgr dSph) have evolved under the gravita tional potential of both Sgr dSph and the Milky Way. The effects of these potentials are most pronounced in the extra-tidal regions as compared to the central regions of the GCs. Aims. We aim to study the extra-tidal regions of the GCs that are possibly associated with Sgr dSph, namely Arp 2, Terzan 8, NGC 5634, NGC 6284, Terzan 7, NGC 2419, NGC 4147, M 54 and Pal 12, using data from the Gaia early data release 3. Methods. We selected the extra-tidal candidates based on their angular distances from the cluster centre in the RA-Dec plane, proper motions of the clusters and the individual extra-tidal star candidates, and their positions on the colour-magnitude diagrams of the clusters. Results. We found extra-tidal candidates for the nine studied GCs. For eight of them, the surface density of candidate extra-tidal stars in the vicinity of the clusters is in significant excess with respect to more distant surrounding fields. No extended extra-tidal features beyond 5 tidal radii were detected for any of the clusters. Conclusions. We publish a list of the most probable extra-tidal candidates that we determined using Gaia astrometric and photometric data. Our analysis shows that the clusters that are associated with Sgr dSph are more likely affected by the gravitational potential of the Sgr, as the distribution of extra-tidal stars is elongated in the same direction as the local stream. NGC 4147 is the only exception. We found some high-probability candidate extra-tidal stars in several of the analysed clusters. We failed to detect any coherent large-scale tidal tail around them
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    Sulfur abundances in the milky way major components
    (Universidad Andrés Bello, 2023) Lucertini, Francesca; Monaco, Lorenzo; Caffau, Elisabetta; Sbordone, Luca; Bonifacio, Piercarlo; Francois, Patrick; Facultad de Ciencias Exactas
    The measurements of chemical abundances and their ratios are a powerful diagnostic to put con straints on both stellar nucleosynthesis and galaxy formation history. For instance, the ratio between elements produced on different timescales, such as α-elements (produced by Supernovae Type-II after ∼30 Myr) and iron (produced by Supernovae Type-Ia on longer timescales), can be used as cosmic clocks. Sulfur is an α-element produced in the final stage of the evolution of massive stars by oxygen convective shell burning and explosive oxygen burning. Moreover, it is moderately volatile so, unlike other α-elements, its abundance measured in stars in the Local Group galaxies can be directly compared to the abundance measured in the gaseous phase in the far Universe, as extra-galactic H II regions or damped Ly-α systems. For these reasons sulfur abundances provide clues on star forma tion history and properties of the interstellar medium, connecting the local and distant Universe. Despite the great potential of this element, most of the available stellar abundances of sulfur come from Galactic stars. Only in the latest years, this analysis was expanded to stars outside the Milky Way. Our view of the behavior of Sulphur in the Milky Way and its satellite is, thus, far from complete. I ran a series of experiments to define the top level requirements needed to measure sulfur abun dances, and I explored the ESO archive looking for available data in a setup adequate for my goal. I identified several interesting public datasets. I focused on the Milky Way major components and, in particular, I found useful data for the Galactic bulge and disk, and a few clusters likely residual of accretion events in the Milky Way (like ω Cen, M 54 and Rup 106). Furthermore, the collaboration with the MINCE project gave me access to high-quality spectra of giant stars at intermediate metallicities in the Milky Way halo. The analysis of this dataset provides important clues about the evolution of Sulphur within the Milky Way. It provides a homogeneous database useful to compare the Milky Way major components with distant systems.
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    The search for extratidal star candidates around Galactic globular clusters NGC 2808, NGC 6266, and NGC 6397 with Gaia DR2 astrometry
    (EDP Sciences, 2021-01) Kundu, Richa; Navarrete, Camila; Fernández-Trincado, José G.; Minniti, Dante; Singh, Harinder P.; Sbordone, Luca; Piatti, Andrés E.; Reylé, Céline
    Abstract Context. Extratidal stars are stellar bodies that end up outside the tidal radius of a cluster as a result of internal processes or external forces acting upon it. The presence and spatial distribution of these stars can give us insights into the past evolution of a cluster inside our Galaxy. Aims. Previous works suggest that globular clusters, when explored in detail, show evidence of extratidal stars. We aim to search for possible extratidal stars in the Galactic globular clusters NGC 6397, NGC 2808, and NGC 6266 using the photometry and proper motion measurements from Gaia DR2 database. Methods. The extratidal stars for the clusters were selected on the basis of: their distance from the cluster center, similarity in their proper motions to the cluster population, and their position on the color-magnitude diagram of the clusters. Each cluster was explored in an annulus disk from the tidal radius up to five times the tidal radii. The significance level of the number of selected extratidal stars was determined on the basis of the distribution of Milky Way stars according to the Besançon Galaxy model and Gaia data. To understand the observed extratidal features, the orbits of the clusters were also determined using GravPot16. Results. Finally, 120, 126, and 107 extratidal candidate stars were found lying outside the tidal radius of the globular clusters NGC 6397, NGC 2808, and NGC 6266, respectively. 70%, 25.4%, and 72.9% of the extratidal stars found are located outside the Jacobi radius of NGC 6397, NGC 2808, and NGC 6266, respectively. The spatial distribution of the extratidal stars belonging to NGC 6397 appears S-like, extending along the curved leading and trailing arms. NGC 2808 has an overdensity of stars in the trailing part of the cluster and NGC 6266 seems to have overdensities of extratidal stars in its eastern and northern sides. Conclusions. Proper motions and color-magnitude diagrams can be used to identify extratidal candidate stars around GCs. Nonetheless, depending on how different the kinematics and stellar populations of a cluster are compared to the Milky Way field, the fraction of contamination can be larger. All three clusters are found to have extratidal stars outside their tidal radii. For NGC 6397 and NGC 2808, these stars may be the result of a combined effect of the disc shocks and tidal disruptions. For NGC 6266, the distribution of extratidal stars is symmetrical around it, most likely indicating that the cluster has an extended stellar envelope.
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    Ítem
    The search for extratidal star candidates around Galactic globular clusters NGC 2808, NGC 6266, and NGC 6397 with Gaia DR2 astrometry
    (EDP Sciences, 2021-01) Kundu, Richa; Navarrete, Camila; Fernández-Trincado, José G; Minniti, Dantee; Singh, Harinder P; Sbordone, Luca; Piatti, Andrés E; Reylé, Céline
    Context. Extratidal stars are stellar bodies that end up outside the tidal radius of a cluster as a result of internal processes or external forces acting upon it. The presence and spatial distribution of these stars can give us insights into the past evolution of a cluster inside our Galaxy. Aims. Previous works suggest that globular clusters, when explored in detail, show evidence of extratidal stars. We aim to search for possible extratidal stars in the Galactic globular clusters NGC 6397, NGC 2808, and NGC 6266 using the photometry and proper motion measurements from Gaia DR2 database. Methods. The extratidal stars for the clusters were selected on the basis of: their distance from the cluster center, similarity in their proper motions to the cluster population, and their position on the color-magnitude diagram of the clusters. Each cluster was explored in an annulus disk from the tidal radius up to five times the tidal radii. The significance level of the number of selected extratidal stars was determined on the basis of the distribution of Milky Way stars according to the Besançon Galaxy model and Gaia data. To understand the observed extratidal features, the orbits of the clusters were also determined using GravPot16. Results. Finally, 120, 126, and 107 extratidal candidate stars were found lying outside the tidal radius of the globular clusters NGC 6397, NGC 2808, and NGC 6266, respectively. 70%, 25.4%, and 72.9% of the extratidal stars found are located outside the Jacobi radius of NGC 6397, NGC 2808, and NGC 6266, respectively. The spatial distribution of the extratidal stars belonging to NGC 6397 appears S-like, extending along the curved leading and trailing arms. NGC 2808 has an overdensity of stars in the trailing part of the cluster and NGC 6266 seems to have overdensities of extratidal stars in its eastern and northern sides. Conclusions. Proper motions and color-magnitude diagrams can be used to identify extratidal candidate stars around GCs. Nonetheless, depending on how different the kinematics and stellar populations of a cluster are compared to the Milky Way field, the fraction of contamination can be larger. All three clusters are found to have extratidal stars outside their tidal radii. For NGC 6397 and NGC 2808, these stars may be the result of a combined effect of the disc shocks and tidal disruptions. For NGC 6266, the distribution of extratidal stars is symmetrical around it, most likely indicating that the cluster has an extended stellar envelope. © ESO 2021.