Highly r-process-enhanced stars are rare and usually metal-poor ([Fe/H] < - 1.0), and mainly populate the Milky Way halo and dwarf galaxies. This study presents the discovery of a relatively bright (V = 12.72), highly r-process-enhanced (r-II) star ([Eu/Fe] = +1.32, [Ba/Eu] = - 0.95), LAMOST J020632.21 + 494127.9. This star was selected from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) medium-resolution (R ~ 7500) spectroscopic survey; follow-up high-resolution (R ~ 25,000) observations were conducted with the High Optical Resolution Spectrograph (HORuS) installed on the Gran Telescopio Canarias (GTC). The stellar parameters (Teff = 4130 K, logg = 1.52, [Fe/H] = −0.54, ξ = 1.80 kms−1) have been inferred taking into account non-local thermodynamic equilibrium (NLTE) effects. The abundances of [Ce/Fe], [Pr/Fe], and [Nd/Fe] are +0.19, +0.65 and +0.64, respectively, relatively low compared to the Solar r-process pattern normalized to Eu. This star has a high metallicity ([Fe/H] = - 0.54) compared to most other highly r-process-enhanced stars, and has the highest measured abundance ratio of Eu to H ([Eu/H] = +0.78). It is classified as a thin-disk star based on its kinematics, and does not appear to belong to any known stream or dwarf galaxy.
@article{arxiv.2407.11572,
title = {Discovery of an Extremely r-process-enhanced Thin-disk Star with [Eu/H] = +0.78},
author = {Xiao-Jin Xie and Jianrong Shi and Hong-Liang Yan and Tian-Yi Chen and Carlos Allende Prieto and Timothy C. Beers and Shuai Liu and Chun-Qian Li and Ming-Yi Ding and Yao-Jia Tang and Ruizhi Zhang and Renjing Xie},
journal= {arXiv preprint arXiv:2407.11572},
year = {2024}
}