The deepest color-magnitude diagrams for the benchmark open cluster NGC,2437 from Gaia and VVVX

Abstract

Deep photometry of Galactic star clusters provides one of the most powerful tools for determining their physical properties. In particular, in low Galactic latitude regions that suffer from heavy extinction and crowding, it is essential to have accurate optical and near-IR photometry for benchmark clusters. NGC,2437 is the most extended star cluster in the near-IR footprint of the VISTA Variables in the Via Lactea Extended Survey (VVVX), covering more than one degree on the sky. In this paper, we aim to characterize the physical properties of NGC,2437 using Gaia data release 3 (DR3) databases in the optical and the VVVX in the near-IR. We use Gaia DR3 proper motions (PMs) to select NGC,2437 members in order to make optical and near-IR color-magnitude and color-color diagrams. We further exploited the newly constructed VVVX deep stack images to obtain the deepest near-IR color-magnitude diagram currently available for this cluster. Using the selected cluster members, we estimate the main physical parameters for NGC,2437, including the mean parallax ̌arpi = 0.608 mas and PMs α* , μ_δ) = (-3.85, 0.41)$ mas/yr. We also estimate a mean reddening of E(J-K_s) = 0.059 mag and an extinction of A_ k_s = 0.034 mag for the NGC,2437 field, with no significant differential reddening spread throughout the field. A distance modulus of $(m-M) = 11.08$ mag is estimated, equivalent to a distance of D=1644 pc. This places NGC,2437 at z=115 pc above the Galactic plane and at a galactocentric distance of R_G = 9.24 kpc. We measure the structural parameters of the cluster by obtaining the core radius r_c=10.79 arcmin. We estimate the total absolute magnitude in the near-IR of M_K = -4.91 mag, equivalent to an optical absolute magnitude of M_V = -3.70 mag. We measure a cluster mean age of rm t = 350 Myr, using the PARSEC-COLIBRI isochrones for solar metallicity. We also measure the binary fraction using the optical and near-IR color-magnitude diagrams. Based on Gaia DR3 data and VVVX deep stacks, we conclude that the NGC,2437 binary fraction is 28.6%. We also discuss the implications of the revised cluster parameters for the nearby open cluster NGC,2425, the planetary nebula NGC,2438, and the evolved OH/IR source OH,231.8+04.2. The VVVX deep stacks increase the photometric depth by approximately 1.6 mag in the K_s band, nearly doubling the number of detected point sources and enabling significantly improved studies of stellar populations throughout the southern Galactic plane.