S21B0102

Using a newly available HSC/NB395 filter developed by our team, which is designed to cover Ca II H&K absorption lines of Galactic stars, we conduct the ZERO (Zero Enrichment Rare Objects) survey - a systematic search for extremely metal-poor stars including possibly zero metal, First stars in the Galaxy, based on deep and wide-field HSC photometry. These stars, formed from chemically pristine interstellar gas, will provide us new insights into the star formation process, the initial mass function, and their dependence on metallicities in the early Universe. Our survey footprint lies within the HSC-SSP Wide layer, where broad-band g and i imaging data are already available, so the combination with NB395 photometry taken in this program will enable us to calibrate and determine photometric metallicities down to [Fe/H] < −3.0. We are targeting stars as faint as g=22 mag, which is deeper than any previous photometric surveys using this approach, thereby enabling us to hunt very metal-poor stars in distant, outer halo regions of the Galaxy.

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