Tracing the Galactic Disk with Gaia DR3: A Deep Study of Berkeley 17, 18, and 39 Open Star Clusters

Abstract

We report a detailed investigation of three intermediate-to-old age open clusters, Berkeley 17, Berkeley 18, and Berkeley 39, utilizing precise astrometric and photometric data from Gaia DR3. Cluster membership was robustly determined through a probabilistic proper-motion analysis, yielding statistically significant samples of 600, 1042, and 907 stars, respectively. From the mean parallaxes of these members, we determine astrometric distances ranging from approximately 3.40 kpc for Berkeley 17 to 5.80 kpc for Berkeley 18. Isochrone fitting applied to the decontaminated color-magnitude diagrams constrains the cluster ages to 9.12 +/- 1.00 Gyr, 3.36 +/- 0.50 Gyr, and 5.10 +/- 0.50 Gyr, respectively. Interstellar reddening spans a wide range, from E(B-V) = 0.17 mag in Berkeley 39 to 0.58 mag in Berkeley 17. Structural parameters derived from King model fits to the radial density profiles, combined with mass function analyses, indicate that the clusters are dynamically relaxed systems with mass distributions broadly consistent with the canonical Salpeter slope. Our kinematic analysis reveals that Berkeley 17, Berkeley 18, and Berkeley 39 are part of the outer disk population.