Jan Kuske, Almudena Arcones, Isak Svensson

The abundances of heavy elements observed in metal-poor, r-process-enhanced stars provide unique information about the astrophysical conditions in which the rapid neutron-capture process (r-process) occurs. We present a Bayesian framework to infer these conditions from stellar abundance patterns. Building on a large site-independent r-process survey, we use a Markov chain Monte Carlo (MCMC) sampler to fit observed abundances with weighted superpositions of abundances from nucleosynthesis calculations, each parameterized by an initial electron fraction, entropy, and expansion timescale. Applying this framework to the nearly complete r-process template star HD222925, we find that two components are required: A heavier H-component producing elements from the second to the third peak and a lighter L-component producing elements from the first to the second peak. Increasing the number of components does not significantly improve the agreement with observations. Extending the analysis to the limited-r stars HD128279 and HD122563, and to the solar r-process residuals, we find that their abundances can be reproduced by almost the same two components, albeit with different relative weights. Moreover, the lightest neutron-capture elements ($Z \lesssim 35$) in the Sun require additional contributions absent in HD222925. Residual discrepancies are concentrated in elements sensitive to observational systematics (e.g., Ag and Cd) or nuclear-physics inputs (around the third peak). Our study highlights the power of combining stellar abundances with nucleosynthesis calculations to constrain the astrophysical conditions of the r-process, and motivates further improvements in both observational data and nuclear-physics inputs.