COMMON ORIGIN of TWO RR LYRAE POPULATIONS and the DOUBLE RED CLUMP in the MILKY WAY BULGE

Young Wook Lee, Sohee Jang

Research output: Contribution to journalArticle

10 Citations (Scopus)

Abstract

A recent survey looking toward the Milky Way bulge has discovered two sequences of RR Lyrae stars on the Period-amplitude diagram with a maximum period-shift of Δ log 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.

Original languageEnglish
Article number236
JournalAstrophysical Journal
Volume833
Issue number2
DOIs
Publication statusPublished - 2016 Dec 20

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clumps
stars
metallicity
shift
metal
chemical evolution
globular clusters
metals
helium
halos
diagram
diagrams
chemical

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

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title = "COMMON ORIGIN of TWO RR LYRAE POPULATIONS and the DOUBLE RED CLUMP in the MILKY WAY BULGE",
abstract = "A recent survey looking toward the Milky Way bulge has discovered two sequences of RR Lyrae stars on the Period-amplitude diagram with a maximum period-shift of Δ log 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.",
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COMMON ORIGIN of TWO RR LYRAE POPULATIONS and the DOUBLE RED CLUMP in the MILKY WAY BULGE. / Lee, Young Wook; Jang, Sohee.

In: Astrophysical Journal, Vol. 833, No. 2, 236, 20.12.2016.

Research output: Contribution to journalArticle

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AB - A recent survey looking toward the Milky Way bulge has discovered two sequences of RR Lyrae stars on the Period-amplitude diagram with a maximum period-shift of Δ log 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.

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