Search for Extremely Metal-Poor Stars with GEMINI-N/GRACES I. Chemical-Abundance Analysis

Abstract

We present stellar parameters and abundances of 13 elements for 18 very metal-poor (VMP; [Fe/H] < -2.0) stars, selected as extremely metal-poor (EMP; [Fe/H] < -3.0) candidates from SDSS and LAMOST survey. High-resolution spectroscopic observations were performed using GEMINI-N/GRACES. We find ten EMP stars among our candidates, and we newly identify three carbon-enhanced metal-poor (CEMP) stars with [Ba/Fe] < 0. Although chemical abundances of our VMP/EMP stars generally follow the overall trend of other Galactic halo stars, there are a few exceptions. One Na-rich star ([Na/Fe] = +1.14) with low [Mg/Fe] suggests a possible chemical connection with second-generation stars in a globular cluster. The progenitor of an extremely Napoor star ([Na/Fe] = -1.02) with an enhancement of K-and Ni-abundance ratios may have undergone a distinct nucleosynthesis episode, associated with core-collapse supernovae (CCSNe) having a high explosion energy. We have also found a Mg-rich star ([Mg/Fe] = +0.73) with slightly enhanced Na and extremely low [Ba/Fe], indicating that its origin is not associated with neutron-capture events. On the other hand, the origin of the lowest Mg abundance ([Mg/Fe] = -0.61) star could be explained by accretion from a dwarf galaxy, or formation in a gas cloud largely polluted by SNe Ia. We have also explored the progenitor masses of our EMP stars by comparing their chemical-abundance patterns with those predicted by Population III SNe models, and find a mass range of 10 -26 M ⊙ , suggesting that such stars were primarily responsible for the chemical enrichment of the early Milky Way.

Hydrodynamics and Nucleosynthesis of Jet-driven Supernovae. I. Parameter Study of the Dependence on Jet Energetics

“…Recently, Jeong et al (2023) made analysis of the high-resolution spectra from stars by the legacy Sloan Digital Sky Survey (SDSS York et al 2000) and the Large sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST Cui et al 2012). They identified 18 very metal-poor stars (VMPS), 10 EMPS and 3 carbonenhanced metal-poor stars (CEMPS), and perform follow-up observations with the Gemini Remote Access to the CFHT ESPaDOnS Spectrograph (GRACES, Chené et al 2021).…”

“…Selected extreme metal-poor stars fromJeong et al (2023). The classification includes VMPS (very metal-poor stars: [Fe/H]< −2), EMPS (extremely metal-poor stars: [Fe/H]< −3), and CEMPS (carbon-enhanced metal-poor stars: [C/Fe]> 1.0).…”