Near-infrared census of RR Lyrae variables in the Messier 3 globular cluster and the period–luminosity relations

Anupam Bhardwaj*, Marina Rejkuba, Richard de Grijs, Gregory J. Herczeg, Harinder P. Singh, Shashi Kanbur, Chow Choong Ngeow

*Corresponding author for this work

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    We present new near-infrared (NIR), JHKs, time-series observations of RR Lyrae variables in the Messier 3 (NGC 5272) globular cluster using the WIRCam instrument at the 3.6 m Canada–France–Hawaii Telescope. Our observations cover a sky area of ∼21′ × 21′ around the cluster center and provide an average of 20 epochs of homogeneous JHKs-band photometry. New homogeneous photometry is used to estimate robust mean magnitudes for 175 fundamental-mode (RRab), 47 overtone-mode (RRc), and 11 mixed-mode (RRd) variables. Our sample of 233 RR Lyrae variables is the largest thus far obtained in a single cluster with time-resolved, multiband NIR photometry. NIR-to-optical amplitude ratios for RR Lyrae in Messier 3 exhibit a systematic increase moving from RRc to short-period (P < 0.6 day) and long-period (P ≳ 0.6 day) RRab variables. We derive JHKs-band period–luminosity relations for RRab, RRc, and the combined sample of variables. Absolute calibrations based on the theoretically predicted period–luminosity–metallicity relations for RR Lyrae stars yield a distance modulus, μ = 15.041± 0.017 (statistical) ± 0.036 (systematic) mag, to Messier 3. When anchored to trigonometric parallaxes for nearby RR Lyrae stars from the Hubble Space Telescope and the Gaia mission, our distance estimates are consistent with those resulting from the theoretical calibrations, albeit with relatively larger systematic uncertainties.

    Original languageEnglish
    Article number220
    Pages (from-to)1-18
    Number of pages18
    JournalAstronomical Journal
    Issue number5
    Publication statusPublished - 1 Nov 2020

    Bibliographical note

    Copyright 2020 The American Astronomical Society. First published in The Astronomical Journal, 160(5), 220, 2020. The original publication is available at, published by IOP Publishing. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.


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