Examinando por Autor "Nataf, David M."

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    Discovery of a nitrogen-enhanced mildly metal-poor binary system: Possible evidence for pollution from an extinct AGB star
    (Astronomy and Astrophysics, 2019) Fernández-Trincado, José G.; Mennickent, Ronald; Cabezas, Mauricio; Zamora, Olga; Martell, Sarah L.; Beers, Timothy C.; Placco, Vinicius M.; Nataf, David M.; Mészáros, Szabolcsk; Minniti, Dantel; Schleicher, Dominik R. G.; Tang, Baitian
    We report the serendipitous discovery of a nitrogen-rich, mildly metal-poor ([Fe/H] = -1.08) giant star in a single-lined spectroscopic binary system found in the SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE-2) survey, Data Release 14 (DR14). Previous work has assumed that two percent of halo giants with unusual elemental abundances have been evaporated from globular clusters, but other origins for their abundance signatures, including binary mass transfer, must also be explored. We present the results of an abundance reanalysis of the APOGEE-2 high-resolution near-infrared spectrum of 2M12451043+1217401 with the Brussels Automatic Stellar Parameter (BACCHUS) automated spectral analysis code. We manually re-derive the main element families, namely light elements (C, N), elements (O, Mg, Si), the iron-peak element (Fe), s-process element (Ce), and light odd-Z element (Al). Our analysis confirms the N-rich nature of 2M12451043+1217401, which has a [N/Fe] ratio of +0.69, and shows that the abundances of C and Al are slightly discrepant from those of a typical mildly metal-poor red giant branch star, but exhibit Mg, Si, O and s-process abundances (Ce) of typical field stars. We also detect a particularly large variability in the radial velocity of this star over the period of the APOGEE-2 observations; the most likely orbit fit to the radial velocity data has a period of 730.89 ±106.86 days, a velocity semi-amplitude of 9.92 ±0.14 km s-1, and an eccentricity of ∼0.1276 ±0.1174. These data support the hypothesis of a binary companion, which has probably been polluted by a now-extinct asymptotic giant branch star.
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    Is Terzan 5 the remnant of a building block of the Galactic bulge? Evidence from APOGEE
    (Oxford University Press, 2022-07-01) Taylor, Dominic J.; Mason, Andrew C.; Schiavon, Ricardo P.; Horta, Danny; Nataf, David M.; Geisler, Doug; Kisku, Shobhit; Phillips, Siân G.; Cohen, Roger E.; Fernández Trincado, José G.; Beers, Timothy C.; Bizyaev, Dmitry; García Hernández, Domingo Aníbal; Lane, Richard R.; Longa Peña, Penélope; Minniti, Dante; Muñoz, Cesar; Pan, Kaike; Villanova, Sandro
    It has been proposed that the globular cluster-like system Terzan 5 is the surviving remnant of a primordial building block of the Milky Way bulge, mainly due to the age/metallicity spread and the distribution of its stars in the α-Fe plane. We employ Sloan Digital Sky Survey data from the Apache Point Observatory Galactic Evolution Experiment to test this hypothesis. Adopting a random sampling technique, we contrast the abundances of 10 elements in Terzan 5 stars with those of their bulge field counterparts with comparable atmospheric parameters, finding that they differ at statistically significant levels. Abundances between the two groups differ by more than 1σ in Ca, Mn, C, O, and Al, and more than 2σ in Si and Mg. Terzan 5 stars have lower [α/Fe] and higher [Mn/Fe] than their bulge counterparts. Given those differences, we conclude that Terzan 5 is not the remnant of a major building block of the bulge. We also estimate the stellar mass of the Terzan 5 progenitor based on predictions by the Evolution and Assembly of GaLaxies and their Environments suite of cosmological numerical simulations, concluding that it may have been as low as ∼3 × 108 M⊙ so that it was likely unable to significantly influence the mean chemistry of the bulge/inner disc, which is significantly more massive (∼1010 M⊙). We briefly discuss existing scenarios for the nature of Terzan 5 and propose an observational test that may help elucidate its origin. © 2022 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.