The Gaia-ESO Survey: the origin and evolution of s-process elements^⋆

¹ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi, 5, 50125 Firenze, Italy
e-mail: laura@arcetri.astro.it
² Monash Centre for Astrophysics, School of Physics and Astronomy, Monash University, VIC 3800, Australia
³ Department of Astronomy, Indiana University, Bloomington, IN, USA
⁴ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, France
⁵ Institute of Astronomy, Madingley Road, University of Cambridge, CB3 0HA, UK
⁶ Space Science Data Center – Agenzia Spaziale Italiana, Via del Politecnico SNC, 00133 Roma, Italy
⁷ INAF – Osservatorio di Astrofisica e Scienza dello Spazio, via Gobetti 93/3, 40129 Bologna, Italy
⁸ Astronomical Observatory, Institute of Theoretical Physics and Astronomy, Vilnius University, av. Saul˙etekio al. 3, 10257 Vilnius, Lithuania
⁹ Instituto de Astrofisica e ciencias do espaço – CAUP, Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
¹⁰ Departamento de Astrofísica, Centro de Astrobiología (INTA-CSIC), ESAC Campus, Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
¹¹ INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
¹² European Southern Observatory, Alonso de Cordova, 3107 Vitacura, Santiago de Chile, Chile
¹³ Departamento de Ciencias Fisicas, Universidad Andres Bello, Fernandez Concha, 700 Las Condes, Santiago, Chile
¹⁴ Lund Observatory, Department of Astronomy and Theoretical Physics, Box 43, 221 00 Lund, Sweden
¹⁵ Astrophysics Group, Keele University, Keele, Staffordshire ST5 5BG, UK
¹⁶ INAF – Padova Observatory, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
¹⁷ Instituto de Astrofísica de Andalucía-CSIC, Apdo. 3004, 18080 Granada, Spain
¹⁸ GEPI, Observatoire de Paris, CNRS, Université Paris Diderot, 5 Place Jules Janssen, 92190 Meudon, France
¹⁹ Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden
²⁰ Laboratoire Lagrange (UMR7293), Université de Nice Sophia Antipolis, CNRS,Observatoire de la Côte d’Azur, CS 34229, 06304 Nice Cedex 4, France
²¹ Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, ul. Bartycka 18, 00-716 Warsaw, Poland
²² Instituto de Física y Astronomiía, Universidad de Valparaiíso, Chile
²³ Millennium Nucleus “Núcleo Planet Formation”, Universidad de Valparaíso, Chile
²⁴ Dipartimento di Fisica e Astronomia, Università di Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
²⁵ Departamento de Didáctica, Universidad de Cádiz, 11519 Puerto Real, Cádiz, Spain
²⁶ INAF – Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
²⁷ Núcleo de Astronomía, Facultad de Ingeniería, Universidad Diego Portales, Av. Ejército, 441 Santiago, Chile
²⁸ Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
²⁹ Universidad de La Laguna, Department of Astrofísica, 38206 La Laguna, Tenerife, Spain

Received: 16 February 2018
Accepted: 5 June 2018

Abstract

Context. Several works have found an increase of the abundances of the s-process neutron-capture elements in the youngest Galactic stellar populations. These trends provide important constraints on stellar and Galactic evolution and they need to be confirmed with large and statistically significant samples of stars spanning wide age and distance intervals.

Aims. We aim to trace the abundance patterns and the time evolution of five s-process elements – two belonging to the first peak, Y and Zr, and three belonging to the second peak, Ba, La, and Ce – using the Gaia-ESO IDR5 results for open clusters and disc stars.

Methods. From the UVES spectra of cluster member stars, we determined the average composition of clusters with ages >0.1 Gyr. We derived statistical ages and distances of field stars, and we separated them into thin and thick disc populations. We studied the time-evolution and dependence on metallicity of abundance ratios using open clusters and field stars whose parameters and abundances were derived in a homogeneous way.

Results. Using our large and homogeneous sample of open clusters, thin and thick disc stars, spanning an age range larger than 10 Gyr, we confirm an increase towards young ages of s-process abundances in the solar neighbourhood. These trends are well defined for open clusters and stars located nearby the solar position and they may be explained by a late enrichment due to significant contribution to the production of these elements from long-living low-mass stars. At the same time, we find a strong dependence of the s-process abundance ratios on the Galactocentric distance and on the metallicity of the clusters and field stars.

Conclusions. Our results, derived from the largest and most homogeneous sample of s-process abundances in the literature, confirm the growth with decreasing stellar ages of the s-process abundances in both field and open cluster stars. At the same time, taking advantage of the abundances of open clusters located in a wide Galactocentric range, these results offer a new perspective on the dependence of the s-process evolution on the metallicity and star formation history, pointing to different behaviours at various Galactocentric distances.