Constraining the Delay Time Distribution of the r - and s -process from Stellar Ages at Solar Metallicity
- 1Max-Planck Institute for Astronomy
- 2Chinese Academy of Sciences
Abstract
We present a new approach to constraining the delay time distribution (DTD) governing r - and s -process element production. Rather than using metallicity as a proxy for time, we work directly with stellar ages at solar metallicity, where chemical equilibrium models are most applicable. We analyze two complementary samples: more than 10,000 red clump (RC) thin disk stars at solar metallicity from LAMOST, and solar twins with high-precision abundances; both have well-determined stellar ages τ . We fit chemical equilibrium models with power-law DTDs to the evolution of [Eu/Mg]( τ ) and [Ba/Mg]( τ ) in each sample, taking europium as a canonical r -process element and barium as an s -process element, each referenced to magnesium as a near-instantaneous, CCSN-dominated element. To validate the method, we first apply it to [Fe/Mg]( τ ) and recover that ≈70% of Fe comes from a delayed channel with a declining DTD ∝ t −1.2 , in agreement with well-established results for iron production in thermonuclear supernovae. It also shows that about 60% of Eu and Ba forming today originate from strongly delayed processes, and the inferred delayed-production rates of both Eu and Ba rise with delay time, opposite to that of thermonuclear supernovae. These results provide direct temporal constraints on r - and s -process enrichment, complementary to metallicity-based chemical evolution studies. Because we model the abundance referenced to Mg, and the same trend is recovered across stars of different guiding-center radii, this appears unaffected by radial migration and chemical evolution varying with Galactocentric radius. If confirmed, it points to delayed neutron-capture production beyond neutron star–neutron star mergers.
Versions
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BibTeX
@article{zhang2026constraining,
title = {{Constraining the Delay Time Distribution of the r - and s -process from Stellar Ages at Solar Metallicity}},
author = {Meng Zhang and Hans-Walter Rix},
journal = {The Astrophysical Journal},
year = {2026},
month = sep,
doi = {10.3847/1538-4357/ae9f4c},
url = {https://iopscience.iop.org/article/10.3847/1538-4357/ae9f4c},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Constraining the Delay Time Distribution of the r - and s -process from Stellar Ages at Solar Metallicity
AU - Meng Zhang
AU - Hans-Walter Rix
PY - 2026
DA - 2026/09/30
JO - The Astrophysical Journal
DO - 10.3847/1538-4357/ae9f4c
UR - https://iopscience.iop.org/article/10.3847/1538-4357/ae9f4c
AB - We present a new approach to constraining the delay time distribution (DTD) governing r - and s -process element production. Rather than using metallicity as a proxy for time, we work directly with stellar ages at solar metallicity, where chemical equilibrium models are most applicable. We analyze two complementary samples: more than 10,000 red clump (RC) thin disk stars at solar metallicity from LAMOST, and solar twins with high-precision abundances; both have well-determined stellar ages τ . We fit chemical equilibrium models with power-law DTDs to the evolution of [Eu/Mg]( τ ) and [Ba/Mg]( τ ) in each sample, taking europium as a canonical r -process element and barium as an s -process element, each referenced to magnesium as a near-instantaneous, CCSN-dominated element. To validate the method, we first apply it to [Fe/Mg]( τ ) and recover that ≈70% of Fe comes from a delayed channel with a declining DTD ∝ t −1.2 , in agreement with well-established results for iron production in thermonuclear supernovae. It also shows that about 60% of Eu and Ba forming today originate from strongly delayed processes, and the inferred delayed-production rates of both Eu and Ba rise with delay time, opposite to that of thermonuclear supernovae. These results provide direct temporal constraints on r - and s -process enrichment, complementary to metallicity-based chemical evolution studies. Because we model the abundance referenced to Mg, and the same trend is recovered across stars of different guiding-center radii, this appears unaffected by radial migration and chemical evolution varying with Galactocentric radius. If confirmed, it points to delayed neutron-capture production beyond neutron star–neutron star mergers.
SN - 0004-637X
SN - 1538-4357
ER -