RR Lyrae Variables in Messier 53: Near-infrared Period–Luminosity Relations and the Calibration Using Gaia Early Data Release 3
Anupam Bhardwaj, Marina Rejkuba, Richard de Grijs, Soung-Chul Yang, Gregory J. Herczeg, Marcella Marconi, Harinder P. Singh, Shashi Kanbur, Chow-Choong Ngeow
Abstract
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 mode (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, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>K</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>s</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mo>−</mml:mo> <mml:mn>2.303</mml:mn> <mml:mo stretchy="false">(</mml:mo> <mml:mn>0.063</mml:mn> <mml:mo stretchy="false">)</mml:mo> <mml:mi>log</mml:mi> <mml:mi>P</mml:mi> <mml:mo>+</mml:mo> <mml:mn>15.212</mml:mn> <mml:mo stretchy="false">(</mml:mo> <mml:mn>0.016</mml:mn> <mml:mo stretchy="false">)</mml:mo> </mml:math> , exhibiting a 1 σ 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 ± 3 μ as in Gaia Early Data Release 3 (EDR3), which increases to 22 ± 2 μ as if the parallax corrections are applied. We also estimate a robust distance modulus, μ M53 = 16.403 ± 0.024 (statistical) ± 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 ω Cen are used to empirically calibrate a new RR Lyrae <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>PLZ</mml:mi> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>K</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>s</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:msub> </mml:math> relation, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>K</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>s</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mo>−</mml:mo> <mml:mn>0.848</mml:mn> <mml:mo stretchy="false">(</mml:mo> <mml:mn>0.007</mml:mn> <mml:mo stretchy="false">)</mml:mo> <mml:mspace width="0.25em"/> <mml:mo>−</mml:mo> <mml:mn>2.320</mml:mn> <mml:mo stretchy="false">(</mml:mo> <mml:mn>0.006</mml:mn> <mml:mo stretchy="false">)</mml:mo> <mml:mi>log</mml:mi> <mml:mi>P</mml:mi> <mml:mo>+</mml:mo> <mml:mn>0.166</mml:mn> <mml:mo stretchy="false">(</mml:mo> <mml:mn>0.011</mml:mn> <mml:mo stretchy="false">)</mml:mo> <mml:mo stretchy="false">[</mml:mo> <mml:mi>Fe</mml:mi> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> <mml:mo stretchy="false">]</mml:mo> </mml:math> , anchored with Gaia EDR3 distances and theoretically predicted relations, and to simultaneously estimate precise RR Lyrae-based distances to these globular clusters.