A Deep Investigation of the Poorly Studied Open Cluster King 18 Using CCD VRI, Gaia DR3 and 2MASS

Abstract In this paper, we re-estimate the astrometric and photometric parameters of the young open star cluster King 18 based on Gaia Data Release 3 (DR3) and 2Mass, then compare them with the results from VRI CCD observations using the f/4.9 Newtonian focus of 74-inch telescope at Kottamia Astronomical Observatory (KAO) in Egypt. King 18 is a poorly studied open star cluster, for which new results are found in the current study. In order to estimate the membership and determine all the astrophysical parameters of the cluster, we use data from Gaia DR3 and KAO. The center, cluster radius, radial density distribution, color-magnitude diagrams, distance, age, and reddening of King 18 are calculated. Also, the luminosity and mass functions, the total mass and the relaxation time of the cluster are estimated. The slope value of the mass function of King 18 is found to be 2.27± 0.17, comparable with Salpeter value. Our estimates for the average cluster age and the relaxation time are 224 ± 6.3 and 28.92 Myrs, respectively. This indicates that the King 18 is dynamically stable and a relaxed cluster. The cluster distance modulus from Gaia, 2Mass and VRI observation has been determined to be 12.38±1.32, 12.32 ±0.107 and 12.28 ±0.29 mag respectively. This results are in good agreement within the error. Moreover the color excesses E(V-I), E(J-K s) and E(G BP-G RP) are 0.85±0.087, 0.38±0.091 and 0.98 ± 0.13 respectively. Finally, the proper motions (µ α cosδ , µ δ), and parallaxes ϖ are-2.603 ± 0.018,-2.106 ± 0.013 and 0.324 ± 0.04 respectively.