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تسجيل مستخدم جديدTargeting Bright Metal-poor Stars in the Disk and Halo Systems of the Galaxy
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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 ($R sim 2000$) spectra, we estimate stellar atmospheric parameters, as well as carbon and magnesium (representative of $alpha$ elements) 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 ($A({rm C}) gtrsim 7.25$) and 97 to Group II ($A({rm C}) lesssim 7.25$) in the Yoon-Beers $A$(C)$-$[Fe/H] diagram. 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] $leq -1.5$, $leq -2.0$, $leq -2.5$ and $leq -3.0$, respectively. Finally, we investigate the presence of dynamically interesting stars in our sample. We find that several VMP/EMP ([Fe/H] $leq -2.5$) stars can be associated with either the disk system or halo substructures like Gaia-Sausage/Enceladus and Sequoia.
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