Discovery of a strongly r-process enhanced extremely metal-poor star LAMOST J110901.22+075441.8

TL;DR

This paper reports the discovery and detailed elemental analysis of an extremely metal-poor star with a strong r-process element enhancement, providing new insights into neutron-capture processes at very low metallicities.

Contribution

It presents the first detailed neutron-capture element measurements in an r-II star at [Fe/H] < -3.4, expanding understanding of r-process enrichment in early stars.

Findings

Star exhibits [Eu/Fe] ~ +1.16, indicating strong r-process enhancement.

Heavy element pattern matches scaled Solar r-process pattern.

Provides the first detailed neutron-capture element data for such low-metallicity r-II stars.

Abstract

We report the discovery of an extremely metal-poor (EMP) giant, LAMOST J110901.22+075441.8, which exhibits large excess of r-process elements with [Eu/Fe] ~ +1.16. The star is one of the newly discovered EMP stars identified from LAMOST low-resolution spectroscopic survey and the high-resolution follow-up observation with the Subaru Telescope. Stellar parameters and elemental abundances have been determined from the Subaru spectrum. Accurate abundances for a total of 23 elements including 11 neutron-capture elements from Sr through Dy have been derived for LAMOST J110901.22+075441.8. The abundance pattern of LAMOST J110901.22+075441.8 in the range of C through Zn is in line with the "normal" population of EMP halo stars, except that it shows a notable underabundance in carbon. The heavy element abundance pattern of LAMOST J110901.22+075441.8 is in agreement with other well studied cool r-II metal-poor giants such as CS 22892-052 and CS 31082-001. The abundances of elements in the range from Ba through Dy well match the scaled Solar r-process pattern. LAMOST J110901.22+075441.8 provides the first detailed measurements of neutron-capture elements among r-II stars at such low metallicity with [Fe/H]<-3.4, and exhibits similar behavior in the abundance ratio of Zr/Eu as well as Sr/Eu and Ba/Eu as other r-II stars.