Learning about the intermediate neutron-capture process from lead abundances

Hampel, Melanie and Karakas, Amanda I. and Stancliffe, Richard J. and Meyer, Bradley S. and Lugaro, Maria (2019) Learning about the intermediate neutron-capture process from lead abundances. ASTROPHYSICAL JOURNAL, 887 (1). ISSN 1538-4357

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Abstract

Lead (Pb) is predominantly produced by the slow neutron-capture process (s process) in asymptotic giant branch (AGB) stars. In contrast t metallicity AGB-models, observations of Magellanic post-AGB stars sho poor (CEMP) stars whose s-process enrichments are accompanied by heav elements traditionally associated with the rapid neutron-capture proces (r process) have raised the need for a neutron-capture process operatin at neutron densities intermediate to the s and r process: the so-calle network calculations. Our i-process models can explain the heavy-elemen abundance patterns measured in Magellanic post-AGB stars including thei puzzlingly low Pb abundances. Furthermore, the heavy-elemen enhancements in the post-AGB and CEMP-i stars, particularly their P abundance, allow us to characterise the neutron densities and exposure of the i process that produced the observed abundance patterns. We fin that the lower-metallicity CEMP-i stars ($\\left[ \\mathrm{Fe} \\mathrm{H} \\right] \\approx -2.5$) have heavy-element abundances bes matched by models with higher neutron densities and exposures ($\\ta > 2.0 \\, \\mathrm{mbarn}^{-1}$) compared to the higher-metallicit post-AGB stars ($\\left[ \\mathrm{Fe} / \\mathrm{H} \\right] \\approx -1.3$ $\\tau < 1.3 \\, \\mathrm{mbarn}^{-1}$). This offers new constraints an insights regarding the properties of i-process sites and demonstrate that the responsible process operates on time scales of the order of few years or less

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