University of Hertfordshire

From the same journal

From the same journal

By the same authors

The COMBS Survey II: Distinguishing the Metal-Poor Bulge from the Halo Interlopers

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  • 200903886v1

    Accepted author manuscript, 6 MB, PDF document

  • Madeline Lucey
  • Keith Hawkins
  • Melissa Ness
  • Victor P. Debattista
  • Alice Luna
  • Martin Asplund
  • Thomas Bensby
  • Luca Casagrande
  • Sofia Feltzing
  • Kenneth C. Freeman
  • Chiaki Kobayashi
  • Anna F. Marino
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Original languageEnglish
Article numberstab003
JournalMonthly Notices of the Royal Astronomical Society
Early online date6 Jan 2021
Publication statusE-pub ahead of print - 6 Jan 2021


The metal-poor stars in the bulge are important relics of the Milky Way's formation history, as simulations predict that they are some of the oldest stars in the Galaxy. In order to determine if they are truly ancient stars, we must understand the origins of this population. Currently, it is unclear if the metal-poor stars in the bulge ([Fe/H] <-1 dex) are merely halo interlopers, a unique accreted population, part of the boxy/peanut-shaped (B/P) bulge or a classical bulge population. In this work, we use spectra from the VLT/FLAMES spectrograph to obtain metallicity estimates using the Ca-II triplet (CaT) of 473 bulge stars (187 of which have [Fe/H] 50\% probability of being bound to the bulge, and half are halo interlopers. We also see that the occurrence rate of halo interlopers increases steadily with decreasing metallicity across the full range of our sample (-3 <[Fe/H] <0.5). Our examination of the kinematics of the confined compared to the unbound stars indicates the metal-poor bulge ([Fe/H] <-1 dex) comprises at least two populations; those confined to the boxy/peanut bulge and halo stars passing through the inner galaxy. We conclude that an orbital analysis approach, as we have employed, is important to uncover and understand the composite nature of the metal-poor stars in the inner region.


This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2021 the Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

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