Stellar population astrophysics (SPA) with the TNG

23 IR elemental abundances of 114 giant stars in 41 open clusters

¹ Materials Science and Applied Mathematics, Malmö University, 205 06 Malmö, Sweden
² Nordic Optical Telescope, Rambla José Ana Fernández Pérez 7, 38711 Breña Baja, Spain
³ Department of Physics, University of Rome Tor Vergata, via della Ricerca Scientifica 1, 00133 Rome, Italy
⁴ INAF-Osservatorio Astronomico di Padova, vicolo dell’ Osservatorio 5, 35122 Padova, Italy
⁵ Dept. of Astronomy & McDonald Observatory, The University of Texas at Austin, 2515 Speedway, Austin, TX 78712, USA
⁶ INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, via Piero Gobetti 93/3, 40129 Bologna, Italy
⁷ Department of Astronomy, Stockholm University, AlbaNova University Center, Roslagstullsbacken 21, 114 21 Stockholm, Sweden
⁸ INAF – Osservatorio Astronomico di Roma, via Frascati 33, 00178 Monte Porzio Catone, Italy
⁹ Fundacíon Galileo Galilei - INAF, Rambla José Ana Fernández Pérez 7, 38712, Breña Baja, Tenerife, Spain

^★ Corresponding author: shilpa.bijavara-seshashayana@mau.se

Received: 11 September 2025
Accepted: 1 November 2025

Abstract

Context. Open clusters have been extensively used as tracers of Galactic chemical evolution, as their constituent stars possess shared characteristics, including age, Galactocentric radius, metallicity, and chemical composition. By examining the trends of elemental abundances with metallicity, age, and Galactocentric radius, valuable insights can be gained into the distribution and nucleosynthetic origins of chemical elements across the Galactic disk. The infrared domain in particular facilitates the observation of some elemental abundances that can be challenging or impossible to discern in the optical; for example, K and F.

Aims. The objective of this study is to derive the stellar parameters and elemental abundances of up to 23 elements in 114 stars spanning 41 open clusters using high-resolution infrared spectroscopy. In addition, the present study aims to examine the chemical evolution of the Galactic disk. This is achieved by investigating radial abundance gradients, variations in abundance between clusters, and the dependence of chemical abundances on the cluster age.

Methods. The spectra utilized in this study were obtained with the high-resolution near-infrared GIANO-B spectrograph at the Telescopio Nazionale Galileo. The derivation of stellar parameters and chemical abundances was achieved by employing the Python version of Spectroscopy Made Easy. In the H-band region, a combination of atomic and molecular features was utilized to constrain the stellar parameters, including OH, CN, and CO molecular lines, and Mg I, Si I, Ti I, Ti II, C I, and Fe I atomic lines.

Results. Abundances for up to 23 elements, C, N, F, Na, Mg, Al, Si, S, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Ce, Nd, and Yb, were derived and compared with available literature values where possible. Non-local thermodynamic equilibrium analysis was utilized for the elements C, Na, Mg, Al, Si, S, K, Ca, Ti, Mn, Fe, and Cu. For each element, Galactic trends were examined by analyzing both [X/Fe] and [X/H] as functions of [Fe/H], stellar age, and Galactocentric radius. In particular, the radial abundance gradient of Ytterbium is presented for the first time, thereby extending the observational constraints on heavy neutron-capture elements.

Conclusions. Radial abundance gradients for a wide range of elements in the Galactic disk are found, with [X/Fe] slopes ranging from −0.061 to +0.065 dex/kpc. The observed gradients are consistent with an inside-out formation scenario for the Galactic disk, wherein chemical enrichment proceeds from the inner regions to the outer ones over time. The observed [X/Fe] trends across multiple nucleosynthetic groups, including α elements, odd-Z elements, iron-peak elements, and neutron-capture elements such as Y, Ce, Nd, and Yb, reflect the diverse production sites and timescales associated with each group. In particular, the positive [Zn/H] and [Zn/Fe] gradients suggest a distinctive nucleosynthetic origin for Zn, possibly linked to metallicity-dependent yields. The positive gradient in [Yb/Fe] (0.065 ± 0.031 dex/kpc) provides significant new constraints on neutron-capture enrichment processes and the chemical evolution of the Galactic disk.