Common Origin of Two RR Lyrae Populations and the Double Red Clump in the Milky Way Bulge

Abstract

A recent survey toward the Milky Way bulge has discovered two sequences of RR Lyrae stars on the period-amplitude diagram with a maximum period-shift of Δlog P = 0.015 between the two populations. Here we show, from our synthetic horizontal-branch models, that this period-shift is most likely due to the small difference in helium abundance (ΔY = 0.012) between the first and second-generation stars (G1 and G2), as is the case in our models for the inner halo globular clusters with similar metallicity ([Fe/H] = -1.1). We further show that the observed double red clump (RC) in the bulge is naturally reproduced when these models are extended to solar metallicity following ΔY/ΔZ = 6 for G2, as would be expected from the chemical evolution models. Therefore, the two populations of RR Lyrae stars and the double RC observed in the bulge appear to be different manifestations of the same multiple population phenomenon in the metal-poor and metal-rich regimes respectively.

arXiv commentAccepted for publication in ApJ

References in corpus (20)

• Multiple populations in globular clusters. Lessons learned from the Milky Way globular clusters
• Na-O Anticorrelation and HB. VII. The chemical composition of first and second-generation stars in 15 globular clusters from GIRAFFE spectra
• Formation and Dynamical Evolution of Multiple Stellar Generations in Globular Clusters
• Quantifying the uncertainties of chemical evolution studies. II. Stellar yields
• Two Red Clumps and the X-Shaped Milky Way Bulge
• The early evolution of Globular Clusters: the case of NGC 2808
• The Split Red Clump of the Galactic Bulge from OGLE-III
• Super Helium-Rich Population and the Origin of Extreme Horizontal-Branch Stars in Globular Clusters
• Deciphering the 3D structure of the old Galactic bulge from the OGLE RR Lyrae stars
• Stellar Models with Enhanced Abundances of C, N, O, Ne, Na, Mg, Si, S, Ca, and Ti, in Turn, at Constant Helium and Iron Abundances
• NGC 6441: another indication for a very high helium content in Globular Cluster stars
• Exploring the Variable Sky with LINEAR. II. Halo Structure and Substructure Traced by RR Lyrae Stars to 30 kpc
• The X-shaped Bulge of the Milky Way revealed by WISE
• CNO abundances in the globular clusters NGC 1851 and NGC 6752
• Star Formation Histories of Globular Clusters with Multiple Populations. I. ω Cen, M22, and NGC 1851
• The Milky Way without X: An alternative interpretation of the double red clump in the Galactic bulge
• Metallicity Analysis of MACHO Galactic Bulge RR0 Lyrae stars from their Lightcurves
• Multiple Populations in Globular Clusters and the Origin of the Oosterhoff Period Groups
• Reinforcing the link between the double red clump and the X-shaped bulge of the Milky Way
• Nucleosynthesis from massive stars 50 years after B2FH

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• Explaining the multiple populations in globular clusters by multiple episodes of star formation and enrichment without gas expulsion from massive star feedback
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• Assembling the Milky Way bulge from globular clusters: Evidence from the double red clump
• The Globular Cluster Origin of the Milky Way Outer Bulge: Evidence from Sodium Bimodality
• Masses of RR Lyrae Stars with Different Chemical Abundances in the Galactic Field
• Impact of distance determinations on Galactic structure. II. Old tracers
• Multiple populations in globular clusters: Unified efforts from stellar evolution and chemical evolution models
• Distribution of red clump stars does not support the X-shaped Galactic bulge
• Are the double-mode bulge RR Lyrae stars with identical period-ratios the relic of a disrupted stellar system?
• New insights on the origin of multiple stellar populations in globular clusters