Precise Empirical Determination of Metallicity Dependence of Near-infrared Period–Luminosity Relations for RR Lyrae Variables

[摘要] RR Lyrae variables are excellent Population II distance indicators thanks to their well-defined period–luminosityrelations (PLRs) at infrared wavelengths. We present results of near-infrared (NIR) monitoring of Galactic globularclusters to empirically quantify the metallicity dependence of NIR PLRs for RR Lyrae variables. Our sampleincludes homogeneous, accurate, and precise photometric data for 964 RR Lyrae variables in 11 globular clusterscovering a large metallicity range (Δ[Fe/H] ∼ 2 dex). We derive JHKs-band period–luminosity–metallicity (PLZ)and period–Wesenheit–metallicity (PWZ) relations anchored using 346 Milky Way field RR Lyrae stars with Gaiaparallaxes, and simultaneously solved for independent distances to globular clusters. We find a significantmetallicity dependence of ∼0.2 mag dex−1 in the JHKs-band PLZ and PWZ relations for RR Lyrae starsindependent of the adopted metallicity scale. The metallicity coefficients and the zero-points of the empirical PLZand PWZ relations are in excellent agreement with the predictions from the horizontal branch evolution andpulsation models. Furthermore, RR Lyrae–based distances to our sample of globular clusters are also statisticallyconsistent with other independent measurements in the literature. Our recommended empirical JHKs-band PLZrelations for RR Lyrae stars with periods of fundamental mode pulsation (Pf) are:( ) ( ) ( ) ( )[ ]( )( ) ( ) ( ) ( )[ ] ( )( ) ( ) ( ) ( )[ ]( )sss=-  -  +  ==-  -  +  ==-  -  +  =M PM PM P0.44 0.03 1.83 0.02 log 0.20 0.02 Fe H 0.05 mag0.74 0.02 2.29 0.02 log 0.19 0.01 Fe H 0.05 mag0.80 0.02 2.37 0.02 log 0.18 0.01 Fe H 0.05 mag .