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Several anomalous elemental abundance ratios have been observed in themetal-poor star HD94028. We assume that its high [As/Ge] ratio is a product ofa weak intermediate (i) neutron-capture process. Given that observationalerrors are usually smaller than predicted nuclear physics uncertainties, wehave first set up a benchmark one-zone i-process nucleosynthesis simulationresults of which provide the best fit to the observed abundances. We have thenperformed Monte Carlo simulations in which 113 relevant (n,$\gamma$) reactionrates of unstable species were randomly varied within Hauser-Feshbach modeluncertainty ranges for each reaction to estimate the impact on the predictedstellar abundances. One of the interesting results of these simulations is adouble-peaked distribution of the As abundance, which is caused by thevariation of the $^{75}$Ga (n,$\gamma$) cross section. This variation stronglyanti-correlates with the predicted As abundance, confirming the necessity forimproved theoretical or experimental bounds on this cross section. The$^{66}$Ni (n,$\gamma$) reaction is found to behave as a major bottleneck forthe i-process nucleosynthesis. Our analysis finds the Pearson product-momentcorrelation coefficient $r_\mathrm{P} > 0.2$ for all of the i-process elementswith $32 \leq Z \leq 42$, with significant changes in their predictedabundances showing up when the rate of this reaction is reduced to itstheoretically constrained lower bound. Our results are applicable to any otherstellar nucleosynthesis site with the similar i-process conditions, such asSakurai's object (V4334 Sagittarii) or rapidly-accreting white dwarfs.

monthly notices of the royal astronomical society

The impact of (n,$\gamma$) reaction rate uncertainties on the predicted  abundances of i-process elements with $32\leq Z\leq 48$ in the metal-poor  star HD94028