The Pristine survey - III. Spectroscopic confirmation of an efficient search for extremely metal-poor stars

The Pristine survey is a narrow-band, photometric survey focused around the wavelength region of the Ca II H&K absorption lines, designed to efficiently search for extremely metal-poor stars. In this work, we use the first results of amedium-resolution spectroscopic follow-up to refine the selection criteria for finding extremely metal-poor stars ([Fe/H]