The Gaia-ESO survey: Mapping the shape and evolution of the radial abundance gradients with open clusters

¹ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
e-mail: laura.magrini@inaf.it
² Institute of Theoretical Physics and Astronomy, Vilnius University, Sauletekio av. 3, 10257 Vilnius, Lithuania
³ INAF – Padova Observatory, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁴ INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Gobetti 93/3, 40129 Bologna, Italy
⁵ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, 06304 Nice, France
⁶ Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia
⁷ ARC Centre of Excellence for Astronomy in Three Dimensions (ASTRO-3D), Canberra, ACT 2611, Australia
⁸ Dipartimento di Fisica, Università degli Studi di Roma Tor Vergata, Via della Ricerca scientifica 1, 00133 Roma, Italy
⁹ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
¹⁰ Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, ul. Bartycka 18, 00-716 Warsaw, Poland
¹¹ ESO, Karl Schwarzschild Strasse 2, 85748 Garching, Germany
¹² Dipartimento di Fisica e Astronomia, Università degli studi di Bologna, Via Gobetti 93/2, 40129 Bologna, Italy
¹³ Lund Observatory, Department of Astronomy and Theoretical Physics, Box 43, 221 00 Lund, Sweden
¹⁴ Space Science Data Center – agenzia Spaziale Italiana, Via del Politecnico, s.n.c., 00133 Roma, Italy
¹⁵ Observational Astrophysics, Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala, Sweden
¹⁶ INAF – Rome Observatory, Via Frascati, 33, Monte Porzio Catone, (RM), Italy
¹⁷ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
¹⁸ Max Planck Institute for Astronomy, Konigstuhl 17, 69117 Heidelberg, Germany
¹⁹ Niels Bohr International Academy, Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, 2100 Copenhagen, Denmark

Received: 12 September 2022
Accepted: 26 October 2022

Abstract

Context. The spatial distribution of elemental abundances and their time evolution are among the major constraints to disentangling the scenarios of formation and evolution of the Galaxy.

Aims. In this paper we used the sample of open clusters available in the final release of the Gaia-ESO survey to trace the Galactic radial abundance and abundance-to-iron ratio gradients, and their time evolution.

Methods. We selected member stars in 62 open clusters, with ages from 0.1 to about 7 Gyr, located in the Galactic thin disc at galactocentric radii (R_GC) from about 6 to 21 kpc. We analysed the shape of the resulting [Fe/H] gradient, the average gradients [El/H] and [El/Fe] combining elements belonging to four different nucleosynthesis channels, and their individual abundance and abundance ratio gradients. We also investigated the time evolution of the gradients dividing open clusters in three age bins.

Results. The [Fe/H] gradient has a slope of −0.054 dex kpc⁻¹. It can be better approximated with a two-slope shape, steeper for R_GC ≤ 11.2 kpc and flatter in the outer regions. We saw different behaviours for elements belonging to different channels. For the time evolution of the gradient, we found that the youngest clusters (age < 1 Gyr) in the inner disc have lower metallicity than their older counterparts and that they outline a flatter gradient. We considered some possible explanations, including the effects of gas inflow and migration. We suggest that the most likely one may be related to a bias introduced by the standard spectroscopic analysis producing lower metallicities in the analysis of low-gravity stars.

Conclusions. To delineate the shape of the ‘true’ gradient, we should most likely limit our analysis to stars with low surface gravity log g >  2.5 and microturbulent parameter ξ <  1.8 km s⁻¹. Based on this reduced sample, we can conclude that the gradient has minimally evolved over the time-frame outlined by the open clusters, indicating a slow and stationary formation of the thin disc over the last 3 Gyr. We found a secondary role of cluster migration in shaping the gradient, with a more prominent role of migration for the oldest clusters.