Examinando por Autor "Anders F."

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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.
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    The Milky Way bar and bulge revealed by APOGEE and Gaia EDR3
    (EDP Sciences, 2021-12-01) Queiroz A.B.A.; Chiappini C.; Perez-Villegas A.; Khalatyan A.; Anders F.; Barbuy B.; Santiago B.X.; Steinmetz M.; Cunha K.; Schultheis M.; Majewski S.R.; Minchev I.; Minniti D.; Beaton R.L.; Cohen R.E.; Da Costa L.N.; Fernández-Trincado J.G.; Garcia-Hernández D.A.; Geisler D.; Hasselquist S.; Lane R.R.; Nitschelm C.; Rojas-Arriagada A.; Roman-Lopes A.; Smith V.; Zasowski G.
    We investigate the inner regions of the Milky Way using data from APOGEE and Gaia EDR3. Our inner Galactic sample has more than 26 500 stars within |XGal|< 5 kpc, |YGal|< 3.5 kpc, |ZGal|< 1 kpc, and we also carry out the analysis for a foreground-cleaned subsample of 8000 stars that is more representative of the bulge-bar populations. These samples allow us to build chemo-dynamical maps of the stellar populations with vastly improved detail. The inner Galaxy shows an apparent chemical bimodality in key abundance ratios [α/Fe], [C/N], and [Mn/O], which probe different enrichment timescales, suggesting a star formation gap (quenching) between the high- and low-α populations. Using a joint analysis of the distributions of kinematics, metallicities, mean orbital radius, and chemical abundances, we can characterize the different populations coexisting in the innermost regions of the Galaxy for the first time. The chemo-kinematic data dissected on an eccentricity-|Z|max plane reveal the chemical and kinematic signatures of the bar, the thin inner disc, and an inner thick disc, and a broad metallicity population with large velocity dispersion indicative of a pressure-supported component. The interplay between these different populations is mapped onto the different metallicity distributions seen in the eccentricity-|Z|max diagram consistently with the mean orbital radius and Vφ distributions. A clear metallicity gradient as a function of |Z|max is also found, which is consistent with the spatial overlapping of different populations. Additionally, we find and chemically and kinematically characterize a group of counter-rotating stars that could be the result of a gas-rich merger event or just the result of clumpy star formation during the earliest phases of the early disc that migrated into the bulge. Finally, based on 6D information, we assign stars a probability value of being on a bar orbit and find that most of the stars with large bar orbit probabilities come from the innermost 3 kpc, with a broad dispersion of metallicity. Even stars with a high probability of belonging to the bar show chemical bimodality in the [α/Fe] versus [Fe/H] diagram. This suggests bar trapping to be an efficient mechanism, explaining why stars on bar orbits do not show a significant, distinct chemical abundance ratio signature.