Exploring the dependence of chemical traits on metallicity

Chemical trends for red giant stars with asteroseismic ages^⋆,⋆⋆

¹ Instituto de Estudios Astrofísicos, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejército Libertador 441, Santiago, Chile
e-mail: sara.vitali@mail.udp.cl
² European Southern Observatory, Alonso de Cordova 3107, Vitacura, Chile
³ Millenium Nucleus ERIS, Chile
⁴ GEPI, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Paris Cité, 5 place Jules Janssen, 92190 Meudon, France
⁵ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁶ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
⁷ Laboratoire de Recherche en Neuroimagerie, University Hospital (CHUV) and University of Lausanne (UNIL), Lausanne, Switzerland
⁸ Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
⁹ DARK, Niels Bohr Institute, University of Copenhagen, Jagtvej 128, 2200 Copenhagen, Denmark

Received: 21 December 2023
Accepted: 28 March 2024

Abstract

Context. Given the massive spectroscopic surveys and the Gaia mission, the Milky Way has turned into a unique laboratory to be explored using abundance ratios that show a strong dependence on time. Within this framework, the data provided through asteroseismology serve as a valuable complement. Even so, it has been demonstrated that chemical traits cannot be used as universal relations across the Galaxy.

Aims. To complete this picture, it is important to investigate the dependence on metallicity of the chemical ratios employed for inferring stellar ages. We aim to explore different combinations of neutron-capture, odd-Z, and α elements as a function of age, particularly focusing on their metallicity dependence for a sample of 74 giant field stars.

Methods. Using UVES observations, we derived atmospheric parameters and high-precision line-by-line chemical abundances (< 0.04 dex) for the entire set of spectra, which covers a wide spread in ages (up to 14 Gyr) and metallicities (−0.7 < [Fe/H] < +0.1). Stellar ages are inferred from astereoseismic information.

Results. By fitting chemical-age trends for three different metallicity groups, we estimated their dependence on metallicity. Simultaneously, we identified those exhibiting stronger correlations with time. We found that the stronger chemical-age relations ([Zr/α]) are not necessarily the ratios with the smaller dependence on metallicity ([Ce/α] and [Ce/Eu]).

Conclusions. We confirm the [n-capture/α]-age trends for evolved stars, wherein the most significant correlation is evident in stars with solar metallicity, gradually diminishing in stars with lower iron content. The lack of homogeneity within the metallicity range highlights the intricate nature of our Galaxy’s star formation history and yield production. The dependence on metallicity of the yields involving s-process elements and the influence of radial stellar migration pose challenges to relying solely on chemical abundances for dating stars. These findings contest the feasibility of establishing universally applicable chemical clocks that are valid across the entire Galaxy and across various metallicity ranges.