Mullen, Joseph P.Joseph P.MullenMarengo, MassimoMassimoMarengoMARTINEZ VAZQUEZ, CLARA EUGENIACLARA EUGENIAMARTINEZ VAZQUEZNeeley, Jillian R.Jillian R.NeeleyBONO, GiuseppeGiuseppeBONODALL'ORA, MassimoMassimoDALL'ORAChaboyer, BrianBrianChaboyerThévenin, FrédéricFrédéricThéveninBRAGA, Vittorio FrancescoVittorio FrancescoBRAGACrestani, JulianaJulianaCrestaniFABRIZIO, MicheleMicheleFABRIZIOFIORENTINO, GiulianaGiulianaFIORENTINOGilligan, Christina K.Christina K.GilliganMONELLI, MatteoMatteoMONELLIStetson, Peter B.Peter B.Stetson2025-03-062025-03-0620210004-637Xhttp://hdl.handle.net/20.500.12386/36460We present newly calibrated period-φ<SUB>31</SUB>-[Fe/H] relations for fundamental-mode RR Lyrae stars in the optical and, for the first time, mid-infrared. This work's calibration data set provides the largest and most comprehensive span of parameter space to date, with homogeneous metallicities from -3 ≲ [Fe/H] ≲ 0.4 and accurate Fourier parameters derived from 1980 ASAS-SN (V band) and 1083 WISE (NEOWISE extension, W1 and W2 bands) RR Lyrae stars with well-sampled light curves. We compare our optical period-φ<SUB>31</SUB>-[Fe/H] relation with those available in the literature and demonstrate that our relation minimizes systematic trends in the lower and higher metallicity range. Moreover, a direct comparison shows that our optical photometric metallicities are consistent with both those from high-resolution spectroscopy and globular clusters, supporting the good performance of our relation. We found an intrinsic scatter in the photometric metallicities (0.41 dex in the V band and 0.50 dex in the infrared) by utilizing large calibration data sets covering a broad metallicity range. This scatter becomes smaller when optical and infrared bands are used together (0.37 dex). Overall, the relations derived in this work have many potential applications, including large-area photometric surveys with James Webb Space Telescope in the infrared and LSST in the optical.STAMPAenArticle10.3847/1538-4357/abefd42-s2.0-85106275852https://iopscience.iop.org/article/10.3847/1538-4357/abefd4https://api.elsevier.com/content/abstract/scopus_id/851062758522021ApJ...912..144MFIS/05 - ASTRONOMIA E ASTROFISICA