Stellar Population Astrophysics (SPA) with the TNG

Non-local thermodynamic equilibrium atmospheric parameters and abundances of giant stars in 33 open clusters^★

¹ INAF – Ossevatorio Astronomico di Padova, vicolo dell’Osservatorio 5, 35122 Padova, Italy
² Department of Physics, University of Rome Tor Vergata, via della Ricerca Scientifica 1, 00133 Rome, Italy
³ Department of Astronomy & McDonald Observatory, The University of Texas at Austin, 2515 Speedway, Austin, TX 78712, USA
⁴ INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, via P. Gobetti 93/3, 40129 Bologna, Italy
⁵ Department of Physics and Astronomy, Monash University, Clayton, VIC 3800, Australia
⁶ ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), Australia
⁷ Center for Computational Astrophysics, Flatiron Institute, 162 5th Avenue, New York, NY 10010, USA
⁸ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁹ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
¹⁰ INAF – Ossservatorio Astrofisico di Catania, via di S. Sofia 78, 95123 Catania, Italy
¹¹ INAF – Osservatorio Astronomico di Roma, via Frascati 33, 00178 Monte Porzio Catone, Italy
¹² Fundacíon Galileo Galilei – INAF, Rambla José Ana Fernández Pérez 7, 38712 Breña Baja, Tenerife, Spain
¹³ Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia

^★★ Corresponding authors: marina.dalponte@inaf.it; valentina.dorazi@inaf.it

Received: 25 February 2025
Accepted: 4 July 2025

Abstract

Context. Open clusters serve as important tools for accurately studying the chemical evolution of the Milky Way. By combining precise chemical data from high-resolution spectra with information on their distances and ages, we can effectively uncover the processes that have shaped our Galaxy.

Aims. This study aims to derive non-local thermodynamic equilibrium (NLTE) atmospheric parameters and chemical abundances for approximately one hundred giant stars across 33 open clusters with near-solar metallicity. The clusters span a wide range of ages, enabling an assessment of the presence and extent of any age-related abundance gradients.

Methods. In the Stellar Population Astrophysics (SPA) project, we acquired new high-resolution spectra of giant stars in a sample of open clusters using the HARPS-N echelle spectrograph at the Telescopio Nazionale Galileo. We chemically characterized nine open clusters for the first time and reanalyzed previously studied SPA clusters, resulting in a consistent and homogeneous sample.

Results. We determined NLTE atmospheric parameters using the equivalent width method and derived NLTE chemical abundances through spectral synthesis for various elements, including α elements (Mg, Si, and Ti), light odd-Z elements (Na, Al), iron-peak elements (Mn, Co, and Ni), and neutron-capture elements (Sr, Y, and Eu). We compared our findings with the existing literature, which revealed a good agreement. We examined the trends of [X/Fe] versus age, confirming previous observations and the enrichment patterns predicted by nucleosynthesis processes. Positive correlations with age are present for a elements such as Mg, Si, Ti, and odd-Z Al, and iron-peak elements Mn, Co, Ni, and Sr, while Na and neutron-capture Y and Eu show a negative trend. This study emphasizes the significance of NLTE corrections and reinforces the utility of open clusters as tracers of Galactic chemical evolution. Furthermore, we provide a benchmark sample of NLTE abundances for upcoming open cluster surveys within large-scale projects, such as 4MOST and WEAVE.