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

Abstract

We present new near-infrared, $JH{K}_s$, Period--Luminosity relations (PLRs) for RR Lyrae variables in the Messier 53 (M53 or NGC 5024) globular cluster. Multi-epoch $JH{K}_s$ 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 $JH{K}_s$-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 $1\ddot{I}ƒ$ 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 $-7\pm 3\hat{I}¼$as in {\it Gaia} Early Data Release 3 (EDR3), which increases to $22\pm 2\hat{I}¼$as if the parallax corrections are applied. We also estimate a robust distance modulus, $\hat{I}{¼}_{\text{M53}}=16.403\pm 0.024$ (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 $\ddot{I}‰$ Cen are used to empirically calibrate a new RR Lyrae PLZ${}_{K_s}$ relation, $K_s=-0.848(0.007)-2.320(0.006)\log P+0.166(0.011)[Fe/H]$, anchored with {\it Gaia} EDR3 distances and theoretically predicted relations, and simultaneously estimate precise RR Lyrae based distances to these globular clusters.

18 pages, 10 figures, 4 Tables, Final Version, Accepted in The Astrophysical Journal