Production of s-process elements in asymptotic giant branch stars as revealed by Gaia/GSP-Spec abundances

¹ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Bd de l’Observatoire, CS 34229, 06304 Nice Cedex 4, France
e-mail: gabriele.contursi@oca.eu
² Departmento de Fısica Teórica y del Cosmos, Universidad de Granada, 18071 Granada, Spain

Received: 14 June 2023
Accepted: 16 September 2023

Abstract

Context. The recent parameterisation by the GSP-Spec module of Gaia/Radial Velocity Spectrometer stellar spectra has produced an homogeneous catalogue of about 174 000 asymptotic giant branch (AGB) stars. Among the 13 chemical elements presented in this Gaia third data release, the abundance of two of them (cerium and neodymium) have been estimated in most of these AGB stars. These two species are formed by slow neutron captures (s-process) in the interior of low- and intermediate-mass stars. They belong to the family of second-peak s-process elements.

Aims. We study the content and production rate of Ce and Nd in AGB stars, using the atmospheric parameters and chemical abundances derived by the GSP-Spec module.

Methods. We defined a working sample of 19 544 AGB stars with high-quality Ce and/or Nd abundances, selected by applying a specific combination of the GSP-Spec quality flags. We compared these abundances with the yield production predicted by AGB evolutionary models.

Results. We first confirmed that the majority of the working sample is composed of AGB stars by estimating their absolute magnitude in the K-band and their properties in a Gaia-2MASS diagram. We also checked that these stars are oxygen-rich AGB stars, as assumed during the GSP-Spec parameterisation. We found a good correlation between the Ce and Nd abundances, confirming the high quality of the derived abundances and that these species indeed belong to the same s-process family. We also found higher Ce and Nd abundances for more evolved AGB stars of similar metallicity, illustrating the successive mixing episodes enriching the AGB star surface in s-process elements formed deeper in their stellar interior. We then compared the observed Ce and Nd abundances with the FRUITY and Monash AGB yields and found that the higher Ce and Nd abundances cannot be explained by AGB stars of masses higher than 5 M_⊙. In contrast, the yields predicted by both models for AGB stars with an initial mass between ∼1.5 and ∼2.5 M_⊙ and metallicities between ∼−0.5 and ∼0.0 dex are fully compatible with the observed GSP-Spec abundances.

Conclusions. This work based on the largest catalogue of high-quality second-peak s-element abundances in oxygen-rich AGB stars allows evolutionary models to be constrained and confirms the fundamental role played by low- and intermediate-mass stars in the enrichment of the Universe in these chemical species.