Nodo ANID

URI permanente para esta colección

https://repositorio.unab.cl/handle/ria/62103

Examinar

Examinando Nodo ANID por Autor "Beers, Timothy C."

Mostrando 1 - 2 de 2
  • No hay miniatura disponible
    Ítem
    Galactic ArchaeoLogIcaL ExcavatiOns (GALILEO): I. An updated census of APOGEE N-rich giants across the Milky Way
    (EDP Sciences, 2022-07-01) Fernández Trincado, José G.; Beers, Timothy C.; Barbuy, Beatriz; Minniti, Dante; Chiappini, Cristina; Garro, Elisa R.; Tang, Baitian; Alves Brito, Alan; Villanova, Sandro; Geisler, Doug; Lane, Richard R.; Diaz, Danilo G.
    We use the 17th data release of the second phase of the Apache Point Observatory Galactic Evolution Experiment (APOGEE-2) to provide a homogenous census of N-rich red giant stars across the Milky Way (MW). We report a total of 149 newly identified N-rich field giants toward the bulge, metal-poor disk, and halo of our Galaxy. They exhibit significant enrichment in their nitrogen abundance ratios ([N/Fe]³a+0.5), along with simultaneous depletions in their [C/Fe] abundance ratios ([C/Fe]< +0.15), and they cover a wide range of metallicities (1.8< [Fe/H]< 0.7). The final sample of candidate N-rich red giant stars with globular-cluster-like (GC-like) abundance patterns from the APOGEE survey includes a grand total of 412 unique objects. These strongly N-enhanced stars are speculated to have been stripped from GCs based on their chemical similarities with these systems. Even though we have not found any strong evidence for binary companions or signatures of pulsating variability yet, we cannot rule out the possibility that some of these objects were members of binary systems in the past and/or are currently part of a variable system. In particular, the fact that we identify such stars among the field stars in our Galaxy provides strong evidence that the nucleosynthetic process(es) producing the anomalous [N/Fe] abundance ratios occurs over a wide range of metallicities. This may provide evidence either for or against the uniqueness of the progenitor stars to GCs and/or the existence of chemical anomalies associated with likely tidally shredded clusters in massive dwarf galaxies such as Kraken/Koala, Gaia-Enceladus-Sausage, among others, before or during their accretion by the MW. A dynamical analysis reveals that the newly identified N-rich stars exhibit a wide range of dynamical characteristics throughout the MW, indicating that they were produced in a variety of Galactic environments. ©
  • No hay miniatura disponible
    Ítem
    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.