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Separating the conjoined red clump in the Galactic bulge: kinematics and abundances

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  • Roberto De Propris
  • R. Michael Rich
  • Andrea Kunder
  • Christian I. Johnson
  • Andreas Koch
  • Sarah Brough
  • Christopher J. Conselice
  • Madusha Gunawardhana
  • David Palamara
  • Kevin Pimbblet
  • Dinuka Wijesinghe
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Article numberL36
<mark>Journal publication date</mark>25/04/2011
<mark>Journal</mark>Astrophysical Journal Letters
Issue number2
Volume732
Number of pages5
Publication StatusPublished
<mark>Original language</mark>English

Abstract

We have used the AAOMEGA spectrograph to obtain R ~ 1500 spectra of 714 stars that are members of two red clumps in the Plaut Window Galactic bulge field (l, b) = (0°, – 8°). We discern no difference between the clump populations based on radial velocities or abundances measured from the Mgb index. The velocity dispersion has a strong trend with Mgb-index metallicity, in the sense of a declining velocity dispersion at higher metallicity. We also find a strong trend in mean radial velocity with abundance. Our red clump sample shows distinctly different kinematics for stars with [Fe/H] <–1, which may plausibly be attributable to a minority classical bulge or inner halo population. The transition between the two groups is smooth. The chemo-dynamical properties of our sample are reminiscent of those of the Milky Way globular cluster system. If correct, this argues for no bulge/halo dichotomy and a relatively rapid star formation history. Large surveys of the composition and kinematics of the bulge clump and red giant branch are needed to further define these trends.

Bibliographic note

5 pages, 4 figures, Accepted for Publication in the Astrophysical Journal Letters Fixed typos, updated affiliations and added some references upon request