RR Lyrae variables in Messier 53: Near-infrared Period--Luminosity relations and the calibration using Gaia Early Data Release 3

TL;DR

This study derives precise near-infrared Period--Luminosity relations for RR Lyrae stars in Messier 53, calibrates them with Gaia EDR3 data, and estimates accurate distances to the cluster and other globular clusters.

Contribution

It provides new near-infrared PLRs for RR Lyrae in M53, calibrates a new empirical PLZ relation using Gaia data, and refines distance measurements to globular clusters.

Findings

Derived tight K_s-band PLR with 0.027 mag dispersion.

Estimated M53 distance modulus as 16.403 mag.

Calibrated a new RR Lyrae PLZ_Ks relation using Gaia EDR3.

Abstract

We present new near-infrared, $JHK_s$, Period--Luminosity relations (PLRs) for RR Lyrae variables in the Messier 53 (M53 or NGC 5024) globular cluster. Multi-epoch $JHK_s$ observations, obtained with the WIRCam instrument on the 3.6-m Canada France Hawaii Telescope, are used for the first time to estimate precise mean-magnitudes for 63 RR Lyrae stars in M53 including 29 fundamental-mode (RRab) and 34 first-overtone modes (RRc) variables. The $JHK_s$-band PLRs for RR Lyrae stars are best constrained for RRab types with a minimal scatter of 22, 23, and 19 mmag, respectively. The combined sample of RR Lyrae is used to derive the $K_s$-band PLR, $K_s = -2.303 (0.063) \log P + 15.212 (0.016)$ exhibiting a $1\sigma$ dispersion of only $0.027$ mag. Theoretical Period--Luminosity--Metallicity (PLZ) relations are used to predict parallaxes for 400 Galactic RR Lyrae resulting in a median parallax zero-point offset of $-7\pm3~\mu$as in {\it Gaia} Early Data Release 3 (EDR3), which increases to $22\pm2~\mu$as if the parallax corrections are applied. We also estimate a robust distance modulus, $\mu_\textrm{M53} = 16.403 \pm 0.024$ (statistical) $\pm 0.033$ (systematic) mag, to M53 based on theoretical calibrations. Homogeneous and precise mean-magnitudes for RR Lyrae in M53 together with similar literature data for M3, M4, M5, and $\omega$ Cen are used to empirically calibrate a new RR Lyrae PLZ$_{K_s}$ relation, $K_s = -0.848 (0.007) -2.320 (0.006) \log P + 0.166 (0.011) {\rm[Fe/H]}$, anchored with {\it Gaia} EDR3 distances and theoretically predicted relations, and simultaneously estimate precise RR Lyrae based distances to these globular clusters.