Origin of missing high-metallicity young-disc s-process enrichment

Determine the physical origin of the missing second-peak s-process enrichment predicted for high-metallicity, young thin-disc stars, including whether uncertainties in asymptotic giant branch nucleosynthesis beyond a simple yield rescaling and a self-consistent treatment of radial migration can reconcile Galactic chemical evolution models with the observed [Ce/Ti] chemical-clock trends.

Background

The Galactic chemical evolution models reproduce the first-peak [Zr/Ti] chemical clock reasonably well but predict a declining [Ce/Ti] trend at young ages, whereas the Kepler data show increasing [Ce/Ti] toward the present day. Modifying high-metallicity AGB-star Ce yields, including multiplying them by factors of 1.5 and 2.0, only partially reduces the discrepancy and fails to reproduce the most Ce-enhanced young stars.

The paper identifies two possible areas requiring further investigation: physically self-consistent revisions to AGB nucleosynthesis and the incorporation of radial migration into the Galactic chemical evolution framework. Radial migration may contribute to the larger observed scatter in abundance–age space and alter the inferred chemical-clock relations.

References

In conclusion, reproducing the behaviour of second s-process peak chemical clocks in the young thin disc remains an open challenge. The origin of the missing s-process enrichment at high metallicity and young ages might be connected to uncertainties in AGB nucleosynthesis that are beyond a simple rescaling, and a self-consistent treatment of radial migration within the GCE framework may further contribute to reconciling models with observations.

— Modelling s-process chemical clocks: insights from high-precision Kepler data  (2608.17480 - Casali et al., 18 Aug 2026) in Section 5, Summary and conclusions

Third, if high-metallicity AGB progenitors were to enhance their s-process production, it is unclear why this effect should selectively boost second-peak elements while leaving first-peak elements unaffected.

— Modelling s-process chemical clocks: insights from high-precision Kepler data  (2608.17480 - Casali et al., 18 Aug 2026) in Section 4, Results and Discussion