A comprehensive study of the stellar cluster ADS 16795 using Gaia DR3 astrometric data

Abstract Open clusters consist of stars that formed at nearly the same time, making them valuable laboratories for testing theories of star formation, stellar evolution, and dynamical processes within the Galactic disc. In this study, we present a detailed astrometric and photometric analysis of the candidate open cluster ADS16795 using Gaia DR3 data. We note that the physical nature of this system is debated in the literature, with some studies classifying it as a moving group or unbound trapezium system. We apply the Hierarchical Density-Based Spatial Clustering of Applications with Noise (HDBSCAN) algorithm to the Gaia Data Release 3 (DR3) astrometric dataset in order to identify probable cluster members and derive the cluster’s fundamental parameters, including its location, age, distance, mass function, and total mass. Applying a minimum membership probability threshold of $$P > 90\%$$ , the HDBSCAN algorithm identified 97 probable member stars. From the derived distance modulus ( $$6.68 \pm 0.05$$ mag) and reddening ( $$0.17 \pm 0.02$$ mag), we obtain a cluster distance of $$0.217 \pm 0.005$$ kpc and an age of $$\log (\textrm{age}) = 7.50 \pm 0.05$$ yr. By fitting PARSEC v1.2S stellar isochrones, we estimate a cluster age of approximately 31.6 Myr and a relaxation time of $$\sim 130$$ Myr. The slope of the present-day mass function ( $$\alpha = -2.65 \pm 0.271$$ ) is in good agreement with the classical Salpeter value. Given the cluster’s young age ( $$\sim 31.6$$ Myr) and low dynamical evolution parameter ( $$\tau = 0.25$$ ), indicating that it has completed only about 25% of its relaxation time, the present-day mass function is expected to closely approximate the initial mass function. The total mass of the detected member stars is estimated to be $$46.6 \pm 0.3 \, M_{\odot }$$ , based solely on the 97 identified probable members and without correction for incompleteness. Using the galpy Python package, we derive the cluster’s kinematics and Galactic orbital parameters from the subset of 17 (of the 97) stars with available Gaia DR3 radial velocity measurements, obtaining a mean radial velocity of $$-14.1\pm {1.2}$$ km s $$^{-1}$$ . In light of these results, we can now revisit the system’s classification: the low dynamical evolution parameter, the young age, and the unbound nature of the system’s trapezium core indicate that ADS16795 is better described as a young, dissolving stellar aggregate or unbound association rather than a gravitationally bound open cluster in the classical sense.