The metallicity dependence of RR Lyrae absolute magnitudes from synthetic horizontal-branch models

Pierre Demarque, Robert Zinn, Young-Wook Lee, Sukyoung Yi

Research output: Contribution to journalArticle

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Abstract

A grid of synthetic horizontal-branch (SHB) models based on horizontal-branch (HB) evolutionary tracks with improved physics has been constructed to reconsider the theoretical calibration of the dependence of Mv(RR) on metallicity in globular clusters and the slope of the mean 〈Mv(RR)〉-[Fe/H] relation. The SHB models confirm Lee's earlier finding that the slope of the 〈Mv(RR)>-[Fe/H] relation is itself a function of the metallicity range considered and that, in addition, for a given [Fe/H] RR Lyrae luminosities depend on HB morphology. This is due to the fact that HB stars pass through the RR Lyrae instability strip at different evolutionary stages, depending on their original position on the HB. At [Fe/H] = -1.9, and for HB type 0, the models yield Mv(RR) = 0.47 ± 0.10. The mean slope for the zero-age HB models is 0.204. Since there is no simple universal relation between Mv(RR) and metallicity that is applicable to all globular clusters, the HB morphology of each individual cluster must be taken into account, in addition to [Fe/H], in deriving the appropriate Mv(RR). Taking HB morphology into account, we find that the slope of the mean 〈Mv(R.R)>-[Fe/H] relation varies between 0.36 for the clusters with Galactocentric distances Rgc. less than 6 kpc and 0.22 for clusters with 6 kpc < Rgc ≤ 20 kpc. Implications for interpreting observations of field RR Lyrae variables and for absolute globular cluster ages and Galactic chronology are briefly discussed.

Original languageEnglish
Pages (from-to)1398-1404
Number of pages7
JournalAstronomical Journal
Volume119
Issue number3
DOIs
Publication statusPublished - 2000 Jan 1

Fingerprint

metallicity
globular clusters
slopes
horizontal branch stars
chronology
strip
physics
grids
luminosity
calibration

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

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abstract = "A grid of synthetic horizontal-branch (SHB) models based on horizontal-branch (HB) evolutionary tracks with improved physics has been constructed to reconsider the theoretical calibration of the dependence of Mv(RR) on metallicity in globular clusters and the slope of the mean 〈Mv(RR)〉-[Fe/H] relation. The SHB models confirm Lee's earlier finding that the slope of the 〈Mv(RR)>-[Fe/H] relation is itself a function of the metallicity range considered and that, in addition, for a given [Fe/H] RR Lyrae luminosities depend on HB morphology. This is due to the fact that HB stars pass through the RR Lyrae instability strip at different evolutionary stages, depending on their original position on the HB. At [Fe/H] = -1.9, and for HB type 0, the models yield Mv(RR) = 0.47 ± 0.10. The mean slope for the zero-age HB models is 0.204. Since there is no simple universal relation between Mv(RR) and metallicity that is applicable to all globular clusters, the HB morphology of each individual cluster must be taken into account, in addition to [Fe/H], in deriving the appropriate Mv(RR). Taking HB morphology into account, we find that the slope of the mean 〈Mv(R.R)>-[Fe/H] relation varies between 0.36 for the clusters with Galactocentric distances Rgc. less than 6 kpc and 0.22 for clusters with 6 kpc < Rgc ≤ 20 kpc. Implications for interpreting observations of field RR Lyrae variables and for absolute globular cluster ages and Galactic chronology are briefly discussed.",
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The metallicity dependence of RR Lyrae absolute magnitudes from synthetic horizontal-branch models. / Demarque, Pierre; Zinn, Robert; Lee, Young-Wook; Yi, Sukyoung.

In: Astronomical Journal, Vol. 119, No. 3, 01.01.2000, p. 1398-1404.

Research output: Contribution to journalArticle

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T1 - The metallicity dependence of RR Lyrae absolute magnitudes from synthetic horizontal-branch models

AU - Demarque, Pierre

AU - Zinn, Robert

AU - Lee, Young-Wook

AU - Yi, Sukyoung

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N2 - A grid of synthetic horizontal-branch (SHB) models based on horizontal-branch (HB) evolutionary tracks with improved physics has been constructed to reconsider the theoretical calibration of the dependence of Mv(RR) on metallicity in globular clusters and the slope of the mean 〈Mv(RR)〉-[Fe/H] relation. The SHB models confirm Lee's earlier finding that the slope of the 〈Mv(RR)>-[Fe/H] relation is itself a function of the metallicity range considered and that, in addition, for a given [Fe/H] RR Lyrae luminosities depend on HB morphology. This is due to the fact that HB stars pass through the RR Lyrae instability strip at different evolutionary stages, depending on their original position on the HB. At [Fe/H] = -1.9, and for HB type 0, the models yield Mv(RR) = 0.47 ± 0.10. The mean slope for the zero-age HB models is 0.204. Since there is no simple universal relation between Mv(RR) and metallicity that is applicable to all globular clusters, the HB morphology of each individual cluster must be taken into account, in addition to [Fe/H], in deriving the appropriate Mv(RR). Taking HB morphology into account, we find that the slope of the mean 〈Mv(R.R)>-[Fe/H] relation varies between 0.36 for the clusters with Galactocentric distances Rgc. less than 6 kpc and 0.22 for clusters with 6 kpc < Rgc ≤ 20 kpc. Implications for interpreting observations of field RR Lyrae variables and for absolute globular cluster ages and Galactic chronology are briefly discussed.

AB - A grid of synthetic horizontal-branch (SHB) models based on horizontal-branch (HB) evolutionary tracks with improved physics has been constructed to reconsider the theoretical calibration of the dependence of Mv(RR) on metallicity in globular clusters and the slope of the mean 〈Mv(RR)〉-[Fe/H] relation. The SHB models confirm Lee's earlier finding that the slope of the 〈Mv(RR)>-[Fe/H] relation is itself a function of the metallicity range considered and that, in addition, for a given [Fe/H] RR Lyrae luminosities depend on HB morphology. This is due to the fact that HB stars pass through the RR Lyrae instability strip at different evolutionary stages, depending on their original position on the HB. At [Fe/H] = -1.9, and for HB type 0, the models yield Mv(RR) = 0.47 ± 0.10. The mean slope for the zero-age HB models is 0.204. Since there is no simple universal relation between Mv(RR) and metallicity that is applicable to all globular clusters, the HB morphology of each individual cluster must be taken into account, in addition to [Fe/H], in deriving the appropriate Mv(RR). Taking HB morphology into account, we find that the slope of the mean 〈Mv(R.R)>-[Fe/H] relation varies between 0.36 for the clusters with Galactocentric distances Rgc. less than 6 kpc and 0.22 for clusters with 6 kpc < Rgc ≤ 20 kpc. Implications for interpreting observations of field RR Lyrae variables and for absolute globular cluster ages and Galactic chronology are briefly discussed.

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