The variable stars population of the extended young globular cluster NGC 1851

Abstract: We report VI CCD photometry of the globular cluster cluster NGC 1851. We aim to study the membership of the variable stars detected in the field of the cluster as listed in the Catalogue of Variable stars in Globular Clusters (CVSGC; Clement et al. 2001) and reported by the Gaia mission. We cross match the two sets of variables to produce light curves that lead to the estimation of physical parameters. The resulting colour-magnitude diagram (CMD), free of likely field stars, enables to confirm the position of the variables, their type and evolutionary stage. We provide new estimations of the period using data acquired on a long timebase. The Fourier decomposition of cluster member RR Lyrae light curves lead to a mean metalicity and distance of ([Fe/H]_{ZW} = -1.35 \pm 0.22) dex and (11.9 \pm 0.6) kpc. The variability and membership of stars reported by Gaia-DR3 as variables in the field of the cluster is discussed.