# Targeting Bright Metal-poor Stars in the Disk and Halo Systems of the Galaxy

**Authors:** Guilherme Limberg, Rafael M. Santucci, Silvia Rossi, Derek Shank, Vinicius M. Placco, Timothy C. Beers, Kevin C. Schlaufman, Andrew R. Casey, Hélio D. Perottoni, Young Sun Lee  
**arXiv:** [2103.07621](https://arxiv.org/abs/2103.07621)  
**Date:** 2021-03-13  
**Summary page:** https://www.summarizepaper.com/en/paper/2103.07621v1/

## Key points

- Spectroscopic follow-up study on 1897 low-metallicity star candidates from the B&B Survey
- Used GMOS-N/S and Goodman spectrographs for observations
- Estimated stellar atmospheric parameters and determined carbon and magnesium abundance ratios
- Confirmed that 56% of program stars are metal-poor, 30% are very metal-poor, and 2% are extremely metal-poor
- Identified 191 carbon-enhanced metal-poor (CEMP) stars, with CEMP fractions of 19% for VMP and 43% for EMP regimes
- Grouped CEMP stars into Group I ($A({\rm C}) \gtrsim 7.25$) and Group II ($A({\rm C}) \lesssim 7.25$)
- Combined data with Gaia EDR3 astrometric information to improve target selection criteria for VMP and EMP stars
- Increased efficiency compared to random draws from B&B catalog, doubling success rates for different metallicity thresholds
- Investigated presence of dynamically interesting stars associated with disk system or halo substructures such as Gaia Sausage/Enceladus and Sequoia with [Fe/H] $\leq -2.5$
- Research based on observations obtained at SOAR telescope and Gemini North/South telescopes

## Summary

This study presents the results of spectroscopic follow-up for 1897 low-metallicity star candidates selected from the Best & Brightest (B&B) Survey. The observations were carried out using the GMOS-N/S and Goodman spectrographs, which provided low-resolution spectra with a resolution of approximately 2000. From these spectra, the authors estimated stellar atmospheric parameters and determined carbon and magnesium abundance ratios, which are representative of alpha elements. The analysis confirmed that 56% of the program stars are metal-poor ([Fe/H] < -1.0), while 30% are classified as very metal-poor (VMP; [Fe/H] < -2.0), and 2% are extremely metal-poor (EMP; [Fe/H] < -3.0). Additionally, the study identified 191 carbon-enhanced metal-poor (CEMP) stars, resulting in CEMP fractions of 19% and 43% for the VMP and EMP regimes, respectively. Among these CEMP stars, 94 belong to Group I ($A({\rm C}) \gtrsim 7.25$) and 97 to Group II ($A({\rm C}) \lesssim 7.25$) in the Yoon-Beers $A$(C)$-$[Fe/H] diagram. To improve target selection criteria for identifying bona fide VMP and EMP stars, the authors combined their data with Gaia EDR3 astrometric information. This approach significantly increased the efficiency compared to random draws from the B&B catalog, more than doubling success rates for different metallicity thresholds: $96\%$, $76\%$, $28\%$, and $4\%$ for [Fe/H] $\leq -1.5$, $\leq -2.0$, $\leq -2.5$, and $\leq -3.0$, respectively. Furthermore, this study investigated the presence of dynamically interesting stars in its sample by associating several VMP/EMP stars with either disk system or halo substructures such as Gaia Sausage/Enceladus and Sequoia with [Fe/H] $\leq -2.5$. The research is partially based on observations obtained under programs at SOAR telescope and Gemini North/South telescopes; SOAR is a joint project between Ministério da Ciência Tecnologia e Inovações do Brasil (MCTI/LNA), US National Science Foundation's NOIRLab (NSF), University of North Carolina at Chapel Hill (UNC), Michigan State University (MSU).