Near-infrared Census of RR Lyrae variables in the Messier 3 globular cluster and the Period--Luminosity Relations

TL;DR

This study provides new near-infrared time-series data for RR Lyrae stars in Messier 3, establishing period-luminosity relations and a precise distance measurement to the cluster, enhancing understanding of variable star properties.

Contribution

It presents the largest homogeneous near-infrared RR Lyrae sample in a single cluster and derives new period-luminosity relations with improved distance calibration.

Findings

Established near-infrared period-luminosity relations for RR Lyrae in Messier 3.

Derived a precise distance modulus of 15.041 mag for Messier 3.

Confirmed consistency between theoretical and parallax-based distance estimates.

Abstract

We present new near-infrared ($JHK_s$) 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 $\sim 21'\times 21'$ around the cluster center and provide an average of twenty epochs of homogeneous $JHK_s$-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, multi-band near-infrared photometry. Near-infrared to optical amplitude ratios for RR Lyrae in Messier 3 exhibit a systematic increase moving from RRc to short-period ($P < 0.6$~days) and long-period ($P \gtrsim 0.6$~days) RRab variables. We derive $JHK_s$-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, $\mu = 15.041 \pm 0.017~(\textrm{statistical}) \pm 0.036~(\textrm{systematic})$~mag, to Messier 3. When anchored to trigonometric parallaxes for nearby RR Lyrae stars from the {\it Hubble Space Telescope} and the {\it Gaia} mission, our distance estimates are consistent with those resulting from the theoretical calibrations, albeit with relatively larger systematic uncertainties.