High-resolution spectroscopy of the young open cluster M 39 (NGC 7092)

Abstract

M 39 is a nearby young open cluster hardly studied in the last few decades. No giant is known among its members and its chemical composition has never been studied. In order to investigate it, we performed high-resolution spectroscopy of 20 expected cluster members with the HARPS and FIES spectrographs. By combining our observations with archival photometry and Gaia-DR3 data we searched for evolved members and studied cluster properties such as the radial velocity, extinction, and age. For the first time, we provide stellar parameters and chemical abundances for 21 species with atomic numbers up to 56. We have not found any new giant as a likely member and we notice a negligible reddening along the cluster field, which we place at 300 pc. We obtain a mean radial velocity for M 39 of −5.5 ± 0.5 km s−1 and an isochrone-fitting age of 430 ± 110 Ma, which corresponds to a MSTO mass of around 2.8 M⊙. This value is consistent with the Li content and chromospheric activity shown by its members. Based on main-sequence stars, the cluster exhibits a solar composition, [Fe/H] = +0.04 ± 0.08 dex, compatible with its Galactocentric location. However, it has a slightly subsolar abundance of Na and an enriched content of neutron-capture elements, specially Ba. In any case, the chemical composition of M 39 is fully compatible with that shown by other open clusters that populate the Galactic thin disc.