The Metallicity Dependence of RR Lyrae Absolute Magnitudes from Synthetic Horizontal-Branch Models | Zendy

P. Demarque | Zendy; R. Zinn | Zendy; YoungWook Lee | Zendy; Sukyoung K. Yi | Zendy

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The Metallicity Dependence of RR Lyrae Absolute Magnitudes from Synthetic Horizontal-Branch Models

Author(s) -

P. Demarque,

R. Zinn,

YoungWook Lee,

Sukyoung K. Yi

Publication year - 2000

Publication title -

the astronomical journal

Language(s) - English

Resource type - Journals

SCImago Journal Rank - 2.61

H-Index - 271

eISSN - 1538-3881

pISSN - 0004-6256

DOI - 10.1086/301261

Subject(s) - rr lyrae variable , globular cluster , horizontal branch , astrophysics , metallicity , instability strip , physics , cluster (spacecraft) , stars , cepheid variable , computer science , programming language

A grid of synthetic horizontal-branch (SHB) models based on HB evolutionarytracks with improved physics has been constructed to reconsider the theoreticalcalibration of the dependence of M_v(RR) on metallicity in globular clusters,and the slope of the mean -[Fe/H] relation. The SHB models confirmLee's earlier finding (Lee 1991) that the slope of the -[Fe/H]relation is itself a function of the metallicity range considered, and that inaddition, 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 instabilitystrip at different evolutionary stages, depending on their original position onthe HB. At [Fe/H]=-1.9, and for HB type 0, the models yield M_v(RR)=0.47 \pm0.10. The mean slope for the zero-age HB models is 0.204. Since there is nosimple universal relation between M_v(RR) and metallicity that is applicable toall globular clusters, the HB morphology of each individual cluster must betaken into account, in addition to [Fe/H], in deriving the appropriate M_v(RR).Taking HB morphology into account, we find that the slope of the mean-[Fe/H] relation varies between 0.36 for the clusters withgalactocentric distances R_gc less than 6 kpc and 0.22 for clusters with6

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