Palladium and silver abundances in stars with [Fe/H] > -2.6

Abstract

Palladium (Pd) and silver (Ag) are the key elements for probing the weak component in the rapid neutron-capture process (r-process) of stellar nucleosynthesis. We performed a detailed analysis of the high-resolution and high signal-to-noise ratio near-UV spectra from the archive of HIRES on the Keck telescope, UVES on the VLT, and HDS on the Subaru Telescope, to determine the Pd and Ag abundances of 95 stars. This sample covers a wide metallicity range with -2.6 $\lesssim$ [Fe/H] $\lesssim$ +0.1, and most of them are dwarfs. The plane-parallel LTE MAFAGS-OS model atmosphere was adopted, and the spectral synthesis method was used to derive the Pd and Ag abundances from Pd I λ 3404 Å and Ag I λ 3280/3382 Å lines. We found that both elements are enhanced in metal-poor stars, and their ratios to iron show flat trends at -0.6 < [Fe/H] < +0.1. The abundance ratios of [Ag/H] and [Pd/H] are well correlated over the whole abundance range. This implies that Pd and Ag have similar formation mechanisms during the Galactic evolution.

15 pages, 12 figures, accepted to A&A

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• The R-Process Alliance: Abundance Universality among Some Elements at and between the First and Second R-Process Peaks
• Diversity of Abundance Patterns of Light Neutron-capture Elements in Very-metal-poor Stars
• Nucleosynthesis in outflows of compact objects and detection prospects of associated kilonovae
• Barium lines in high-quality spectra of two metal-poor giants in the Galactic halo