Time evolution of Ce as traced by APOGEE using giant stars observed with the Kepler, TESS and K2 missions

Abstract

Context. Abundances of slow neutron-capture process (s-process) elements in stars with exquisite asteroseismic, spectroscopic, and astrometric constraints offer a novel opportunity to study stellar evolution, nucleosynthesis, and Galactic chemical evolution. Aims. We investigate one of the least studied s-process elements in the literature, cerium (Ce), using stars with asteroseismic constraints from the Kepler, K2, and TESS missions. Methods. We combined the global asteroseismic parameters derived from precise light curves obtained by the Kepler, K2, and TESS missions with stellar parameters and chemical abundances from the latest data release of the large spectroscopic survey APOGEE and astrometric data from the Gaia mission. Finally, we computed stellar ages using the code PARAM with a Bayesian estimation method. Results. We investigated the different trends of [Ce/Fe] as a function of metallicity, [α/Fe], and age taking into account the dependence on the radial position, especially in the case of K2 targets, which cover a wide galactocentric range. We finally explored the [Ce/α] ratios as a function of age in different galactocentric intervals. Conclusions The studied trends display a strong dependence of the Ce abundances on the metallicity and star formation history. The [Ce/Fe] ratio shows a non-monotonic dependence on [Fe/H] with a peak around −0.2 dex. Moreover, younger stars have higher [Ce/Fe] and [Ce/α] ratios than older stars, confirming the latest contribution of low- and intermediate-mass asymptotic giant branch stars to the Galactic chemical enrichment. In addition, the trends of [Ce/Fe] and [Ce/α] with age become steeper moving towards the outer regions of the Galactic disc, demonstrating more intense star formation in the inner regions than in the outer regions. Cerium is thus a potentially interesting element to help constrain stellar yields and the inside-out formation of the Milky Way disc. However, the large scatter in all the relations studied here suggests that spectroscopic uncertainties for this element are still too large.