The independence of the mid-infrared RR Lyrae Period-Luminosity relation from metallicity from a study of three globular clusters in the Large Magellanic Cloud
Abstract
RR Lyrae are pulsating variable stars tracing old (>10 Gyr) stellar populations, and exhibit a strong mid-infrared Period-Luminosity (PL) relation that can be calibrated with known parallaxes to infer distances. Here we present Period-Luminosity relations and distance moduli for three isolated globular clusters in the Large Magellanic Cloud: Reticulum, NGC 1841, and NGC 1466. Our analysis uses legacy \textit{Spitzer Space Telescope} images obtained by the Carnegie RR Lyrae Program, and an internally self-consistent sample restricted to RRab stars, with cluster membership confirmed using Gaia DR3 proper motions and photometry. In the Spitzer 3.6~μm band, we simultaneously fit a PL for these clusters using a slope derived from Galactic Globular Clusters, yielding extinction-corrected distance moduli of 18.47±0.09 mag for Reticulum, 18.29±0.09 mag for NGC 1841, and 18.61±0.09 mag for NGC 1466. The latter two are the first RR Lyrae PL-based distance moduli for these clusters, and all three are consistent with literature values from other techniques. Additionally we fit a PL with slope as a free parameter, and find that this LMC-derived PL is consistent with that derived from Galactic GCs. Simultaneously fitting a PLZ for the three clusters yields a metallicity coefficient c= −0.03±0.05 mag dex−1 which can be considered a negligible dependence of the PL on metallicity (|c| <0.1 mag dex−1). Modelling an intrinsic width, W, to the PL/ PLZ yields a consistent value W≈0.1±0.02 mag, suggesting intrinsic width is not driven by metallicity.
Versions
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BibTeX
@misc{ardern2026independence,
title = {{The independence of the mid-infrared RR Lyrae Period-Luminosity relation from metallicity from a study of three globular clusters in the Large Magellanic Cloud}},
author = {Steve Ardern and Vicky Scowcroft and Stijn Wuyts},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.21494},
eprint = {2609.21494},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.21494},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - The independence of the mid-infrared RR Lyrae Period-Luminosity relation from metallicity from a study of three globular clusters in the Large Magellanic Cloud
AU - Steve Ardern
AU - Vicky Scowcroft
AU - Stijn Wuyts
PY - 2026
DA - 2026/09/18
PB - arXiv
DO - 10.48550/arxiv.2609.21494
UR - https://arxiv.org/abs/2609.21494
AB - RR Lyrae are pulsating variable stars tracing old (>10 Gyr) stellar populations, and exhibit a strong mid-infrared Period-Luminosity (PL) relation that can be calibrated with known parallaxes to infer distances. Here we present Period-Luminosity relations and distance moduli for three isolated globular clusters in the Large Magellanic Cloud: Reticulum, NGC 1841, and NGC 1466. Our analysis uses legacy \textit{Spitzer Space Telescope} images obtained by the Carnegie RR Lyrae Program, and an internally self-consistent sample restricted to RRab stars, with cluster membership confirmed using Gaia DR3 proper motions and photometry. In the Spitzer 3.6~μm band, we simultaneously fit a PL for these clusters using a slope derived from Galactic Globular Clusters, yielding extinction-corrected distance moduli of 18.47±0.09 mag for Reticulum, 18.29±0.09 mag for NGC 1841, and 18.61±0.09 mag for NGC 1466. The latter two are the first RR Lyrae PL-based distance moduli for these clusters, and all three are consistent with literature values from other techniques. Additionally we fit a PL with slope as a free parameter, and find that this LMC-derived PL is consistent with that derived from Galactic GCs. Simultaneously fitting a PLZ for the three clusters yields a metallicity coefficient c= −0.03±0.05 mag dex^−1 which can be considered a negligible dependence of the PL on metallicity (|c| <0.1 mag dex^−1). Modelling an intrinsic width, W, to the PL/ PLZ yields a consistent value W≈0.1±0.02 mag, suggesting intrinsic width is not driven by metallicity.
ER -