Astrophysical sites of the intermediate neutron-capture (i) process · revision history

Revision 2

Accepted · core change · record

Changes against revision 1:

Title
Astrophysical sites of the intermediate neutron-capture (i) process
Plain
Some old stars show heavy-element patterns that neither the slow nor the rapid neutron-capture process can explain, suggesting an in-between process with medium neutron fluxes. Which kind of star produces this flux is not known.
Precise · changed · core
Revision 1: The i-process operates at neutron densities $n_n \sim 1e13 \text{ to } 1e16\,\mathrm{cm}^{-3}$, between the s-process ($\sim 1e7 \text{ to } 1e10\,\mathrm{cm}^{-3}$) and the r-process ($> 1e20\,\mathrm{cm}^{-3}$), and is invoked for carbon-enhanced metal-poor stars with mixed s and r signatures, Sakurai's object and some presolar grains. Identify which candidate sites (proton ingestion into helium-flash convective zones of low-metallicity AGB and super-AGB stars, rapidly accreting white dwarfs, helium shells of massive stars) produce the observed $[\mathrm{Ba}/\mathrm{La}]$, $[\mathrm{La}/\mathrm{Eu}]$ and $[\mathrm{Ba}/\mathrm{Eu}]$ ratios, and with what neutron exposure, given the large uncertainties in neutron-capture rates on unstable nuclei near $A \sim 130 \text{ to } 140$.
Revision 2: The i-process operates at neutron densities $n_n \sim 10^{13} \text{ to } 10^{16}\,\mathrm{cm}^{-3}$, between the s-process ($\sim 10^{7} \text{ to } 10^{10}\,\mathrm{cm}^{-3}$) and the r-process ($> 10^{20}\,\mathrm{cm}^{-3}$), and is invoked for carbon-enhanced metal-poor stars with mixed s and r signatures, Sakurai's object and some presolar grains. Identify which candidate sites (proton ingestion into helium-flash convective zones of low-metallicity AGB and super-AGB stars, rapidly accreting white dwarfs, helium shells of massive stars) produce the observed $[\mathrm{Ba}/\mathrm{La}]$, $[\mathrm{La}/\mathrm{Eu}]$ and $[\mathrm{Ba}/\mathrm{Eu}]$ ratios, and with what neutron exposure, given the large uncertainties in neutron-capture rates on unstable nuclei near $A \sim 130 \text{ to } 140$.
Settled by
Multidimensional hydrodynamic models of proton ingestion that yield the neutron exposure without free parameters, combined with measured or constrained capture rates on the key unstable isotopes, reproducing the abundance patterns of i-process stars.
Kind
phenomenon
Answer type
identification
References
(empty)
Literature status
open
Status note
2025 studies extended AGB i-process models to actinides and short-lived radionuclides and built statistical frameworks for its nuclear uncertainties.
Posed since
1977

Decisions