Discovery of a New Stellar Subpopulation Residing in the (Inner) Stellar Halo of the Milky Way

José G. Fernández-Trincado, Timothy C. Beers, Vinicius M. Placco, Edmundo Moreno, Alan Alves-Brito, Dante Minniti, Baitian Tang, Angeles Pérez-Villegas, Céline Reylé, Annie C. Robin, Sandro Villanova

Research output: Contribution to journalArticlepeer-review

28 Citations (Scopus)

Abstract

We report the discovery of a unique collection of metal-poor giant stars that exhibit anomalously high levels of 28Si, clearly above typical Galactic levels. Our sample spans a narrow range of metallicities, peaking at -1.07 ± 0.06, and exhibits abundance ratios of [Si, Al/Fe] that are as extreme as those observed in Galactic globular clusters (GCs), and Mg is slightly less overabundant. In almost all the sources we used, the elemental abundances were redetermined from high-resolution spectra, which were reanalyzed assuming LTE. Thus, we compiled the main element families, namely, the light elements (C, N), α-elements (O, Mg, Si), iron-peak element (Fe), s-process elements (Ce, Nd), and the light odd-Z element (Al). We also provide dynamical evidence that most of these stars lie on tight (inner) halo-like and retrograde orbits passing through the bulge. Such kinds of objects have been found in present-day halo GCs, providing the clearest chemical signature of past accretion events in the (inner) stellar halo of the galaxy, possibly formed as the result of dissolved halo GCs. Their chemical composition is, in general, similar to that of typical GC populations, although several differences exist.

Original languageEnglish
Article numberL8
JournalAstrophysical Journal Letters
Volume886
Issue number1
DOIs
Publication statusPublished - 20 Nov 2019

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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