Chemical Evolution of R-process Elements in Stars (CERES): IV. An observational run-up of the third r-process peak with Hf, Os, Ir, and Pt

The third r-process peak (Os, Ir, Pt) is poorly understood due to observational challenges, with spectral lines located in the blue or near-ultraviolet region of stellar spectra. These challenges need to be overcome for a better understanding of the r-process in a broader context. To understand how...

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Published in:arXiv.org 2024-11
Main Authors: Arthur Alencastro Puls, Kuske, Jan, Camilla Juul Hansen, Lombardo, Linda, Visentin, Giorgio, Arcones, Almudena, Raphaela Fernandes de Melo, Reichert, Moritz, Bonifacio, Piercarlo, Caffau, Elisabetta, Fritzsche, Stephan
Format: Article
Language:English
Subjects:
Abundance
Chemical analysis
Chemical evolution
Chemical synthesis
Decoupling
Line spectra
Local thermodynamic equilibrium
Metallicity
Nuclear fusion
Rare earth elements
Red giant stars
Signal to noise ratio
Stellar evolution
Stellar spectra
Ultraviolet spectra
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Summary:The third r-process peak (Os, Ir, Pt) is poorly understood due to observational challenges, with spectral lines located in the blue or near-ultraviolet region of stellar spectra. These challenges need to be overcome for a better understanding of the r-process in a broader context. To understand how the abundances of the third r-process peak are synthesised and evolve in the Universe, a homogeneous chemical analysis of metal-poor stars using high quality data observed in the blue region of the electromagnetic spectrum (< 400 nm) is necessary. We provide a homogeneous set of abundances for the third r-process peak (Os, Ir, Pt) and Hf, increasing by up to one order of magnitude their availability in the literature. A classical 1D, local thermodynamic equilibrium (LTE) analysis of four elements (Hf, Os, Ir, Pt) is performed, using ATLAS model atmospheres to fit synthetic spectra in high resolution (> 40,000), high signal-to-noise ratio, of 52 red giants observed with UVES/VLT. Due to the heavy line blending involved, a careful determination of upper limits and uncertainties is done. The observational results are compared with state-of-the-art nucleosynthesis models. Our sample displays larger abundances of Ir (Z=77) in comparison to Os (Z=76), which have been measured in a few stars in the past. The results also suggest decoupling between abundances of third r-process peak elements with respect to Eu (rare earth element) in Eu-poor stars. This seems to contradict a co-production scenario of Eu and the third r-process peak elements Os, Ir, and Pt in the progenitors of these objects. Our results are challenging to explain from the nucleosynthetic point of view: the observationally derived abundances indicate the need for an additional early, primary formation channel (or a non-robust r-process).
ISSN:2331-8422