Stellar Population Astrophysics (SPA) with the TNG

α-elements, lithium, sodium and aluminum in 16 open clusters^⋆

¹ Dipartimento di Fisica e Astronomia, Universitá di Padova, Vicolo Osservatorio 2, 35122 Padova, Italy
e-mail: ruyuan.zhang@studenti.unipd.it
² INAF-Osservatorio Astronomico di Padova, Vicolo Osservatorio 5, 35122 Padova, Italy
³ Institute for Advanced Studies, Technische Universität München, Lichtenbergstraße 2 a, 85748 Garching bei München, Germany
⁴ INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via P. Gobetti 93/3, 40129 Bologna, Italy
⁵ INAF-Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123 Catania, Italy
⁶ Fundación Galileo Galilei-INAF, Rambla José Ana Fernández Pérez 7, 38712 Breña Baja, Tenerife, Spain
⁷ INAF-Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monte Porzio Catone, Italy
⁸ Dipartimento di Fisica e Astronomia, Universitá degli Studi di Firenze, Via G. Sansone 1, 50019 Sesto Fiorentino, Firenze, Italy
⁹ KIAA-The Kavli Institute for Astronomy and Astrophysics at Peking University, Beijing 100871, PR China
¹⁰ INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi, 5, 50125 Firenze, Italy
¹¹ Dipartimento di Fisica e Astronomia, Universitá degli Studi di Bologna, Via Gobetti 93/2, 40129 Bologna, Italy
¹² Leibniz Institute for Astrophysics Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany

Received: 20 March 2022
Accepted: 21 July 2022

Abstract

Context. Exploring the Galactic chemical evolution and enrichment scenarios with open clusters (OCs) allows us to understand the history of the Milky Way disk. High-resolution spectra of OCs are a crucial tool, as they provide precise chemical information, to combine with precise distances and ages.

Aims. The aim of the Stellar Population Astrophysics (SPA) project is to derive homogeneous and accurate comprehensive chemical characterization of a number of poorly studied OCs.

Methods. Using the HARPS-N echelle spectrograph at the Telescopio Nazionale Galileo (TNG), we obtained high-resolution spectra of giant stars in 18 OCs, 16 of which are chemically characterized for the first time, and two of which are well studied for comparison. The OCs in this sample have ages from a few tens of Myr to 4 Gyr, with a prevalence of young clusters. We already presented the radial velocities and atmospheric parameters for them in a previous SPA paper. Here, we present results for the α-elements O, Mg, Si, Ca and Ti, and the light elements Na and Al, all determined by the equivalent width method. We also measured Li abundance through the synthesis method.

Results. We discuss the behaviors of lithium, sodium and aluminum in the context of stellar evolution. For Na and Al, we compare our findings with models to investigate their behaviors as a function of mass, suggesting that Na mixing to the surface might start in masses as low as 2 M_⊙. We study the radial, vertical, and age trends for the measured abundance ratios in a sample that combines our results and recent literature for OCs, finding significant (positive) gradients only for [Mg/Fe] and [Ca/Fe] in all cases. Finally, we compare O and Mg in the combined sample with chemo-dynamical models, finding a good agreement for intermediate-age and old clusters. There is a sharp increase in the abundance ratios measured among very young clusters (age < 300 Myr), accompanied by a poorer fit with the models for O and Mg, likely related to the inadequacy of traditional model atmospheres and methods in the derivation of atmospheric parameters and abundance ratios for stars of such young ages.