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), Two Micron All-sky Survey (2MASS) and 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 have used 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 ( $\alpha$ ) of King 18 is found to be 2.27± 0.17, which is 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 King 18 is dynamically stable and a relaxed cluster. The cluster distance modulus from Gaia, 2Mass and VRI observations has been determined to be 12.380 ± 1.320, 12.320 ± 0.107 and 12.280 ± 0.290 mag respectively, which corresponds to distances of 2992.26, 2910.72 and 2857.59 pc, respectively. These results are in good agreement within the error. Moreover the color excesses E(V-I), E(J- ${\text{K}}_s$ ) and E( ${\text{G}}_{\mathrm{BP}}$ - ${\text{G}}_{\mathrm{RP}}$ ) are 0.850 ± 0.087, 0.380 ± 0.091 and 0.980 ± 0.130 respectively. Finally, the proper motions ( ${\mu }_{\alpha }$ cos $\delta$ , ${\mu }_{\delta }$ ), and parallaxes ( $\varpi$ ) are $-2.603\pm 0.018$ , $-2.106\pm 0.013$ and 0.324 ± 0.040, respectively.

Keywords: 2Mass; CMD; Distance; Gaia DR3; Membership; Parallax; Proper motion; Star cluster.