Stellar Population Astrophysics (SPA) with TNG. Atmospheric parameters of members of 16 unstudied open clusters

Open clusters are ideal test objects for Galactic chemical and dynamical evolution and for stellar evolution theory. Recently, 16 open clusters have been analized, 14 of them never or scarcely studied before. All target stars were selected from the Gaia-based colour-magnitude diagrams with the aim of deriving their metallicity and detailed chemical composition. Metallicity is important for the study of the chemical evolution of the disc and for determining with better precision the cluster age through comparison with stellar models of appropriate composition.

The radial and vertical gradients of metallicity have been derived, adding also data from large-scale spectroscopic surveys or similar projects, together with metallicity distribution in age. These distributions generally agree well with chemodynamical models of Galactic evolution. The exception found for very young open clusters (which are numerous in the sample) may be explained with difficulties intrinsic to the analysis of stars of these ages, already found in other studies and generally producing unrealistically low levels of metallicity.

The study has been performed in the framework of the Stellar Population Astrophysics (SPA) project, a Large Programme at the Telescopio Nazionale Galileo (PI: L. Origlia). SPA derives the detailed chemical properties of the Solar neighborhood with high precision employing GIARPS (the combination of the very high-resolution spectrographs GIANO and HARPS-N). A specific Working Group, lead by A. Bragaglia, is then active within SPA to observe and study these stellar aggregates. The team targets both very close clusters where a large part of the main sequence can be observed and more far away clusters where only a few giants are accessible to GIARPS.

Link at the Astronomy & Astrophysics paper: Zhang et al. Arxiv.

LEFT: Gaia Bp-Rp vs Gmag CMDs of the 16 new and 2 comparison OCs (the stars are coloured by membership probability, Cantat-Gaudin et al. 2018, 2020), with larger symbols indicating the giants observed with GIARPS. RIGHT, upper panel: comparison between the radial velocities measured from our spectra and the values in Gaia DR2, where larger differences or errorbars are for the binary systems. RIGHT, lower panels: radial metallicity distribution defined by OCs, where we plot the SPA clusters and those in Gaia-ESO, APOGEE, GALAH, and OCCASO. We separate the OCs in three age ranges (age<2 Gyr, where most of the SPA clusters are; 2-4 Gyr; <4 Gyr) and in the paper we compare to chemical evolutionary models (Minchev et al. 2014).
[Adapted from: Zhang R., Lucatello S., Bragaglia A., Carrera R., Spina L., Alonso-Santiago J., Andreuzzi G., Casali G., Carretta E., Frasca A., Fu X., Magrini L., Origlia L., D’Orazi V., Vallenari A. 2021, A&A, in press, Arxiv ]

For the interested reader, other SPA papers on open clusters are: