New Optical and Mid-Infrared RR Lyrae Period-Luminosity-Metallicity Relations for Precision Distances and Metallicity Distributions in the Magellanic Clouds
Abstract
RR Lyrae (RRL) stars, thanks to the existence of their period-luminosity relations, have been widely used as primary standard candles within the Milky Way and the Local Group of galaxies. We present in this work the latest empirical RRL period-luminosity-metallicity (PLZ) and period-Wesenheit-metallicity (PWZ) relations combining optical ($V, I$) and mid-infrared data (W1) using OGLE and WISE photometry, anchored to Gaia DR3 parallaxes. We calibrate these relations with the largest, most complete, and homogeneous catalog of Galactic halo field RRL spectroscopic metallicities. These new PLZ/PWZ relations provide distance measurements in remarkable agreement with those derived from eclipsing binaries in the Large and Small Magellanic Clouds (MC): (m−M)0, LMC = 18.47 ± 0.07 (stat) ± 0.05 (sys) mag and (m−M)0, SMC = 18.87 ± 0.09 (stat) ± 0.06 (sys) mag (within 1% and 10% of eclipsing binary distances, respectively). We have also re-calibrated photometric metallicity relations to derive individual [Fe/H] abundances of LMC and SMC RRL stars. This allowed us to investigate the metallicity gradient of the MCs and discover two distinct populations of fundamental mode RRL stars in the LMC (only one is instead found in the SMC). Our newly derived mid-infrared period-luminosity relations are poised to become an essential tool to derive precise distances of older stellar populations in the Local Group of galaxies, and can easily be adapted to observations obtained in JWST NIRCam photometric bands.
Related
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BibTeX
@misc{martinezvazquez2026optical,
title = {{New Optical and Mid-Infrared RR Lyrae Period-Luminosity-Metallicity Relations for Precision Distances and Metallicity Distributions in the Magellanic Clouds}},
author = {Clara E. Martínez-Vázquez and Joseph P. Mullen and Massimo Marengo and Giuseppe Bono and Vittorio F. Braga and Santi Cassisi and Brian Chaboyer and Massimo Dall'Ora and Valentina D'Orazi and Michele Fabrizio and Giuliana Fiorentino and Matteo Monelli and Peter B. Stetson and Frédéric Thévenin},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.27119},
eprint = {2609.27119},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.27119},
}
RIS
TY - UNPB
TI - New Optical and Mid-Infrared RR Lyrae Period-Luminosity-Metallicity Relations for Precision Distances and Metallicity Distributions in the Magellanic Clouds
AU - Clara E. Martínez-Vázquez
AU - Joseph P. Mullen
AU - Massimo Marengo
AU - Giuseppe Bono
AU - Vittorio F. Braga
AU - Santi Cassisi
AU - Brian Chaboyer
AU - Massimo Dall'Ora
AU - Valentina D'Orazi
AU - Michele Fabrizio
AU - Giuliana Fiorentino
AU - Matteo Monelli
AU - Peter B. Stetson
AU - Frédéric Thévenin
PY - 2026
DA - 2026/09/22
PB - arXiv
DO - 10.48550/arxiv.2609.27119
UR - https://arxiv.org/abs/2609.27119
AB - RR Lyrae (RRL) stars, thanks to the existence of their period-luminosity relations, have been widely used as primary standard candles within the Milky Way and the Local Group of galaxies. We present in this work the latest empirical RRL period-luminosity-metallicity (PLZ) and period-Wesenheit-metallicity (PWZ) relations combining optical ($V, I$) and mid-infrared data (W1) using OGLE and WISE photometry, anchored to Gaia DR3 parallaxes. We calibrate these relations with the largest, most complete, and homogeneous catalog of Galactic halo field RRL spectroscopic metallicities. These new PLZ/PWZ relations provide distance measurements in remarkable agreement with those derived from eclipsing binaries in the Large and Small Magellanic Clouds (MC): (m−M)_0, LMC = 18.47 ± 0.07 (stat) ± 0.05 (sys) mag and (m−M)_0, SMC = 18.87 ± 0.09 (stat) ± 0.06 (sys) mag (within 1% and 10% of eclipsing binary distances, respectively). We have also re-calibrated photometric metallicity relations to derive individual [Fe/H] abundances of LMC and SMC RRL stars. This allowed us to investigate the metallicity gradient of the MCs and discover two distinct populations of fundamental mode RRL stars in the LMC (only one is instead found in the SMC). Our newly derived mid-infrared period-luminosity relations are poised to become an essential tool to derive precise distances of older stellar populations in the Local Group of galaxies, and can easily be adapted to observations obtained in JWST NIRCam photometric bands.
ER -