The Milky Way without X: An alternative interpretation of the double red clump in the Galactic bulge

Young Wook Lee, Seok Joo Joo, Chul Chung

Research output: Contribution to journalArticlepeer-review

41 Citations (Scopus)


The presence of two red clumps (RCs) in high-latitude fields of the Milky Way bulge is interpreted as evidence for an X-shaped structure originated from the bar instability. Here we show, however, that this double RC phenomenon is more likely to be another manifestation of multiple populations observed in globular clusters (GCs) in the metal-rich regime. As in the bulge GC Terzan 5, the helium enhanced second-generation stars in the classical bulge component of the Milky Way are placed on the bright RC, which is about 0.5 mag brighter than the normal RC originated from the first-generation stars, producing the observed double RC. In a composite bulge, where a classical bulge can coexist with a boxy pseudo bulge, our models can also reproduce key observations, such as the dependence of the double RC feature on metallicity and Galactic latitude and longitude. If confirmed by Gaia trigonometric parallax distances, this would indicate that the Milky Way bar is not sufficiently buckled to form the X-shaped structure in the bulge, and suggest that the early-type galaxies would be similarly prevailed by super-helium-rich subpopulation.

Original languageEnglish
Pages (from-to)3906-3911
Number of pages6
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Publication statusPublished - 2015 Nov 11

Bibliographical note

Publisher Copyright:
© 2015 The Authors.

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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