Heavy Puzzle Pieces: Learning About the i Process from Pb Abundances

We examine the observed heavy-element abundances of two types of objects that show enrichments in s-process elements but whose abundance patterns are generally incompatible with s-process predictions: CEMP-i stars and Pb-poor post-AGB stars, with representative metallicities around \(\left[ \mathrm {Fe} / \mathrm {H} \right] \approx -2.5 \) and \(\left[ \mathrm {Fe} / \mathrm {H} \right] \approx -1.3 \), respectively. We can explain these abundance patterns, including the puzzlingly low Pb abundances of post-AGB stars, as results of i-process nucleosynthesis. To do this we use nuclear-network calculations to study heavy-element production at different constant neutron densities up to \(n = 10^{15}\,\mathrm {cm}^{-3}\). The constraints posed by measured Pb abundances in these objects, allow us to characterise the neutron densities and exposures of the process responsible for creating the observed heavy-element abundances.