Examinando por Autor "Vieira K."

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    Aluminium-enriched metal-poor stars buried in the inner Galaxy
    (EDP Sciences, 2020-11) Fernández-Trincado J.G.; Beers T.C.; Minniti D.; Tang B.; Villanova S.; Geisler D.; Pérez-Villegas A.; Vieira K.
    Stars with higher levels of aluminium and nitrogen enrichment are often key pieces in the chemical makeup of multiple populations in almost all globular clusters (GCs). There is also compelling observational evidence that some Galactic components could be partially built from dissipated GCs. The identification of such stars among metal-poor field stars may therefore provide insight into the composite nature of the Milky Way (MW) bulge and inner stellar halo, and could also reveal other chemical peculiarities. Here, based on APOGEE spectra, we report the discovery of 29 mildly metal-poor ([Fe/H] -0.7) stars with stellar atmospheres strongly enriched in aluminium (Al-rich stars: [Al/Fe] +0.5), well above the typical Galactic levels, located within the solar radius toward the bulge region, which lies in highly eccentric orbits (e 0.6). We find many similarities for almost all of the chemical species measured in this work with the chemical patterns of GCs, and therefore we propose that they have likely been dynamically ejected into the bulge and inner halo from GCs formed in situ and/or GCs formed in different progenitors of known merger events experienced by the MW, such as the Gaia-Sausage-Enceladus and/or Sequoia. © 2020 ESO.
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    Atypical Mg-poor Milky Way Field Stars with Globular Cluster Second-generation-like Chemical Patterns
    (Institute of Physics Publishing, 2017-09) Fernández-Trincado J.G.; Zamora O.; Garcia-Hernández D.A.; Souto, Diogo; Dell'Agli F.; Schiavon R.P.; Geisler D.; Tang B.; Villanova S.; Hasselquist, Sten; Mennickent R.E.; Cunha, Katia; Shetrone M.; Prieto, Carlos Allende; Vieira K.; Zasowski G.; Sobeck J.; Hayes C.R.; Majewski S.R.; Placco V.M.; Beers T.C.; Schleicher D.R.G.; Robin A.C.; Mészáros, Sz.; Masseron T.; Pérez, Ana E. Garcia; Anders F.; Meza A.; Alves-Brito A.; Carrera R.; Minniti D.; Lane R.R.; Fernández-Alvar E.; Moreno E.; Pichardo B.; Pérez-Villegas A.; Schultheis M.; Roman-Lopes A.; Fuentes C.E.; Nitschelm C.; Harding P.; Bizyaev D.; Pan K.; Oravetz D.; Simmons A.; Ivans, Inese; Blanco-Cuaresma S.; Hernández J.; Alonso-Garcia J.; Valenzuela O.; Chanamé J.
    We report the peculiar chemical abundance patterns of 11 atypical Milky Way (MW) field red giant stars observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE). These atypical giants exhibit strong Al and N enhancements accompanied by C and Mg depletions, strikingly similar to those observed in the so-called second-generation (SG) stars of globular clusters (GCs). Remarkably, we find low Mg abundances ([Mg/Fe] < 0.0) together with strong Al and N overabundances in the majority (5/7) of the metal-rich ([Fe/H] -1.0) sample stars, which is at odds with actual observations of SG stars in Galactic GCs of similar metallicities. This chemical pattern is unique and unprecedented among MW stars, posing urgent questions about its origin. These atypical stars could be former SG stars of dissolved GCs formed with intrinsically lower abundances of Mg and enriched Al (subsequently self-polluted by massive AGB stars) or the result of exotic binary systems. We speculate that the stars Mg-deficiency as well as the orbital properties suggest that they could have an extragalactic origin. This discovery should guide future dedicated spectroscopic searches of atypical stellar chemical patterns in our Galaxy, a fundamental step forward to understanding the Galactic formation and evolution. © 2017. The American Astronomical Society. All rights reserved.