University of Hertfordshire

From the same journal

From the same journal

By the same authors

The COMBS Survey -- III. The Chemodynamical Origins of Metal-Poor Bulge Stars

Research output: Contribution to journalArticlepeer-review


  • Madeline Lucey
  • Keith Hawkins
  • Melissa Ness
  • Tyler Nelson
  • Victor P. Debattista
  • Alice Luna
  • Thomas Bensby
  • Kenneth C. Freeman
  • Chiaki Kobayashi
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Original languageEnglish
Number of pages24
JournalMonthly Notices of the Royal Astronomical Society
Early online date6 Oct 2021
Publication statusPublished - 1 Jan 2022


The characteristics of the stellar populations in the Galactic Bulge inform and constrain the Milky Way's formation and evolution. The metal-poor population is particularly important in light of cosmological simulations, which predict that some of the oldest stars in the Galaxy now reside in its center. The metal-poor bulge appears to consist of multiple stellar populations that require dynamical analyses to disentangle. In this work, we undertake a detailed chemodynamical study of the metal-poor stars in the inner Galaxy. Using R$\sim$ 20,000 VLT/GIRAFFE spectra of 319 metal-poor (-2.55 dex$\leq$[Fe/H]$\leq$0.83 dex, with $\overline{\rm{[Fe/H]}}$=-0.84 dex) stars, we perform stellar parameter analysis and report 12 elemental abundances (C, Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Mn, Zn, Ba, and Ce) with precisions of $\approx$0.10 dex. Based on kinematic and spatial properties, we categorise the stars into four groups, associated with the following Galactic structures: the inner bulge, the outer bulge, the halo, and the disk. We find evidence that the inner and outer bulge population is more chemically complex (i.e., higher chemical dimensionality and less correlated abundances) than the halo population. This result suggests that the older bulge population was enriched by a larger diversity of nucleosynthetic events. We also find one inner bulge star with a [Ca/Mg] ratio consistent with theoretical pair-instability supernova yields and two stars that have chemistry consistent with globular cluster stars.


© 2021 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society.

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