High-resolution Spectroscopic Follow-up Observation Results for 13 Extremely Metal-poor Candidates Selected by Narrowband Photometry

Extremely metal-poor (EMP; [Fe/H] < −3.0) stars preserve key information about the earliest stages of Galactic chemical evolution. Based on a training set of spectroscopic metallicities, we constructed catalogs of more than 120,000 EMP candidates from large-scale narrowband photometric surveys. To validate this approach, we obtained high-resolution CFHT/ESPaDOnS spectra for 13 candidates selected from the SkyMapper-based catalog. The follow-up observation confirms that the narrowband photometric selection is effective in identifying very metal-poor (VMP) stars and retaining a substantial EMP fraction: four targets are confirmed as EMP stars, and all targets remain VMP with [Fe/H] < −2.4. The photometric metallicities are systematically lower than the spectroscopic values by 0.44 dex, with a relatively small scatter of 0.19 dex, indicating a systematic offset in the photometric metallicity scale that could be reduced through improved calibration. Abundances for more than 20 chemical species are derived, leading to the identification of a new potassium-enhanced r -II star, J2001-1215. By combining chemical abundances with orbital properties, five stars are found to be dynamically consistent with known Galactic substructures, including Gaia–Sausage–Enceladus (GES), Thamnos, and Sequoia. These stars provide high-resolution chemical measurements for the EMP regime of these Galactic substructures. These results underscore the role of narrowband photometry in efficiently selecting EMP candidates for targeted high-resolution spectroscopic follow-up, thereby enabling detailed chemical and dynamical studies of the early Milky Way.