Search for Extremely Metal-Poor ([Fe/H] < -3.0) Stars with GEMINI

Friday, 18 August 2023 11 a.m. — noon MST

AURA Recinto

NOIRLab South Colloquia
Miji Jeong (Chungnam National University)

Population III stars are believed to have led the chemical enrichment of the early universe, thereby influencing the formation of subsequent generations of stars. Understanding their physical properties is essential for comprehending the origins of chemical elements and the evolution history of the early Milky Way. Due to their significant mass, Pop III stars no longer exist, preventing direct observation and study. However, by investigating the detailed chemical abundance patterns preserved in the atmospheres of Extremely Metal-Poor(EMP) stars - considered genuine second-generation stars - we can indirectly gain insights into the characteristics of the first-generation stars and the environment of the early universe. In this presentation, I will present the stellar parameters and abundances of 13 elements in a total of 18 stars, which were selected as potential EMP candidates from the SDSS and LAMOST surveys. Our high-resolution spectroscopic observations, collected using GEMINI-N/GRACES over the past five years, have confirmed that out of the candidates: 8 are identified as very metal-poor ([Fe/H] < –2.0) stars, and 10 are indeed EMP ( [Fe/H] < -3.0) stars. While the chemical abundances of our VMP/EMP stars generally align with the overall trends observed in other Galactic halo stars, there are a few exceptions. I will discuss the possible origins of these chemically peculiar objects. Furthermore, I have investigated the progenitor masses of EMP stars by comparing their chemical-abundance patterns with predictions from Pop III SNe models. This analysis has revealed a mass range of 10-26 M, indicating that these stars played a crucial role in enriching the early Milky Way. Finally, I will share the preliminary results of GHOST data obtained during the SV run and ongoing research using GRACES.