Targeting Bright Metal-poor Stars in the Disk and Halo Systems of the Galaxy
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
Abstract
Abstract We present the results of spectroscopic follow-up for 1897 low-metallicity star candidates, selected from the Best & Brightest (B&B) Survey, carried out with the GMOS-N/S (Gemini North/South telescopes) and Goodman (SOAR Telescope) spectrographs. From these low-resolution ( R ∼ 2000) spectra, we estimate stellar atmospheric parameters, as well as carbon and magnesium abundance ratios. We confirm that 56% of our program stars are metal-poor ([Fe/H] < − 1.0), 30% are very metal-poor (VMP; [Fe/H] < − 2.0), and 2% are extremely metal-poor (EMP; [Fe/H] < − 3.0). There are 191 carbon-enhanced metal-poor (CEMP) stars, resulting in CEMP fractions of 19% and 43% for the VMP and EMP regimes, respectively. A total of 94 confirmed CEMP stars belong to Group I ( A (C) ≳ 7.25) and 97 to Group II ( A (C) ≲ 7.25) in the Yoon–Beers A (C)−[Fe/H] diagram. Moreover, we combine these data with Gaia EDR3 astrometric information to delineate new target-selection criteria, which have been applied to the Goodman/SOAR candidates, to more than double the efficiency for identification of bona fide VMP and EMP stars in comparison to random draws from the B&B catalog. We demonstrate that this target-selection approach can achieve success rates of 96%, 76%, 28%, and 4% for [Fe/H] ≤ − 1.5, ≤ − 2.0, ≤ − 2.5 and ≤ − 3.0, respectively. Finally, we investigate the presence of dynamically interesting stars in our sample. We find that several VMP/EMP ([Fe/H] ≤ − 2.5) stars can be associated with either the disk system or halo substructures like Gaia-Sausage/Enceladus and Sequoia.