CCD Photometry of the globular cluster NGC 5466. RR Lyrae light curve decomposition and the distance scale

Abstract

We report the results of CCD V and r photometry of the globular cluster NGC 5466. The difference image analysis technique adopted in this work has resulted in accurate time series photometry even in crowded regions of the cluster enabling us to discover five probably semi-regular variables. We present new photometry of three previously known eclipsing binaries and six SX Phe stars. The light curves of the RR Lyrae stars have been decomposed in their Fourier harmonics and their fundamental physical parameters have been estimated using semi-empirical calibrations. The zero points of the metallicity, luminosity and temperature scales are discussed and our Fourier results are transformed accordingly. The average iron abundance and distance to the Sun derived from individual RR Lyrae stars, indicate values of [Fe/H]=-1.91 +- 0.19 and D = 16.0 +- 0.6 kpc, or a true distance modulus of 16.02 +- 0.09 mag, for the parent cluster. These values are respectively in the Zinn & West metallicity scale and in agreement with recent luminosity determinations for the RR Lyrae stars in the LMC. The M_V-[Fe/H] relation has been recalibrated as M_V=+(0.18+-0.03)[Fe/H]+(0.85+-0.05) using the mean values derived by the Fourier technique on RR Lyrae stars in a family of clusters. This equation predicts M_V=0.58 mag for [Fe/H]=-1.5, in agreement with the average absolute magnitude of RR Lyrae stars calculated from several independent methods. The M_V-[Fe/H] relationship and the value of [Fe/H] have implications on the age of the globular clusters when determined from the magnitude difference between the horizontal branch and the turn off point (HB-TO method). The above results however would not imply a change in the age of NGC 5466, of 12.5+-0.9 Gyr, estimated from recent isochrone fitting.

17 pages, MNRAS Accepted

References in corpus (1)

• CCD Photometry of the globular cluster M2. RR Lyrae physical parameters and new variables

Cited by in corpus (6)

• Accurate distances to Galactic globular clusters through a combination of Gaia EDR3, HST and literature data
• Detection of a White Dwarf companion to a Blue Straggler Star in the outskirts of globular cluster NGC 5466 with the Ultraviolet Imaging Telescope (UVIT)
• A Census of Variability in Globular Cluster M68 (NGC 4590)
• Characteristics of bright ab-type RR Lyrae stars from the ASAS and WASP surveys
• Variable stars in the bulge globular cluster NGC 6401
• A vindication of the RR Lyrae Fourier light curve decomposition for the calculation of metallicity and distance in globular clusters