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

TL;DR

This study measures palladium and silver abundances in 95 stars across a wide metallicity range to understand their nucleosynthesis origins, revealing similar formation mechanisms during Galactic evolution.

Contribution

First detailed analysis of Pd and Ag abundances in a large, diverse stellar sample using high-resolution spectra and spectral synthesis methods.

Findings

Pd and Ag are enhanced in metal-poor stars.

Their ratios to iron are flat at certain metallicities.

Pd and Ag abundances are well correlated across the sample.

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 {\lambda} 3404 {\AA} and Ag I {\lambda} 3280/3382 {\AA} 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.