Discovery of an Extremely r-process-enhanced Thin-disk Star with [Eu/H] = +0.78

• Published in: arXiv.org
• Main Authors: Xiao-Jin, Xie, Shi, Jianrong, Hong-Liang, Yan, Tian-Yi, Chen, Carlos Allende Prieto, Beers, Timothy C, Liu, Shuai, Chun-Qian, Li, Ming-Yi, Ding, Yao-Jia, Tang, Zhang, Ruizhi, Xie, Renjing
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 14.09.2024
• Subjects: Abundance; Dwarf galaxies; Iron; Kinematics; Local thermodynamic equilibrium; Metallicity; Physics - Astrophysics of Galaxies; Physics - Solar and Stellar Astrophysics; Sky surveys (astronomy); Spectroscopic telescopes; Spectroscopy
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2407.11572

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 (\({T_{\rm eff}}\) = 4130 K, \(\rm log\,g \) = 1.52, \( \rm[Fe/H] \) = \( - \)0.54, \(\xi\) = 1.80 \( \rm{km\,{s^{-1}}} \)) 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.