I. N. Kallimanis

Context . Open clusters are excellent tracers of the Galactic thin disk, providing insights into its formation and evolution. Precise cluster age determination is essential for studying cluster evolution as well as the evolution of the disk as a whole. Aims . With this work, our aim was to produce an updated catalog of cluster parameters (age, extinction, distance) by constraining cluster ages via newly available spectroscopic measurements of metallicity. Methods . Using high-quality astrometry from Gaia Data Release 3, we derived new cluster memberships via a machine learning-based clustering algorithm (AstroLink). We compiled metallicity measurements from multiple ground-based spectroscopic surveys (Gaia-ESO, GALAH DR3, APOGEE-OCCAM) and Gaia GSP-Spec into a uniform scale. The ages of 320 clusters were determined using a machine learning-accelerated approximate Bayesian isochrone-fitting code (based on ASteCA), adopting a multiband approach that incorporates Gaia XP and synthetic photometry. Results . This work resulted in a robust sample of open clusters with precisely determined parameters and uncertainties. In addition, this catalog may provide a foundation for machine learning models to infer parameters for a larger sample of objects without spectroscopic data, which is to be explored in future work.

NGC 2509 is a distant (≈2.5 kpc) and little-studied open cluster located in the third Galactic quadrant. It is a moderately old cluster, whose age has not yet been precisely determined. The main-sequence stars in NGC 2509 follow a narrow distribution in the colormagnitude diagram, unlike other clusters of similar age. In addition, its chemical composition has never been investigated. To address these issues and characterize the cluster we performed moderate- and high-resolution spectroscopy with FLAMES@VLT of 132 stars, both dwarfs and giants, which represents a significant fraction (≈73%) of likely members. We provide atmospheric stellar parameters and, for the first time, chemical abundances for 21 species with atomic numbers up to 60. In our analysis we followed two different methodologies, both of which will be used for the incoming WEAVE stellar surveys. We find an average radial velocity for NGC 2509 of 58.6±1.3km s ⁻¹ and a mild supersolar metallicity ([Fe/H]≈0.1 dex). This value is slightly higher than expected according to its galactocentric distance, but still compatible with the Galactic gradient. From the lithium content of the dwarfs and the isochrone-fitting method we obtain an age for NGC 2509 of 1.26±0.3Gyr. The reddening across the cluster field is negligible ( A _V = 0.25 ± 0.02 mag). The cluster peculiar main sequence turnoff is due to a narrow distribution of the rotational velocities peaking at v sin i ≈ 80 km s ⁻¹ , with little dispersion. The chemical pattern of NGC 2509 follows the Galactic trends shown by other open clusters in the Galactic thin disk.