Efficiency and success rates of the Pristine survey from spectroscopic follow-up

The Pristine survey uses narrow-band photometry on the region of the Ca II H & K absorption lines to find extremely metal-poor stars. With a spectroscopic follow-up sample of 205 stars in the magnitude range 14 < V < 18, we compute the success rates for finding extremely metal-poor stars and modify the selection criteria used to select stars for follow-up. This reduces the sample to 149 stars, and from these we report success rates of 22% for recovering stars with [Fe/H] < -3.0 and 70% for [Fe/H] < -2.5. When compared to previous works that search for extremely metal-poor stars, the success rates of Pristineshow an improvement in efficiency by a factor of ~4 - 5.