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

Abstract

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 a medium-resolution spectroscopic follow-up to refine the selection criteria for finding extremely metal-poor stars ($\text{[Fe/H]}\le -3.0$) in the Pristine survey. We consider methods by which stars can be selected from available broad-band and infrared photometry plus the additional Pristine narrow-band photometry. The spectroscopic sample presented in this paper consists of 205 stars in the magnitude range $14<V<18$. Applying the photometric selection criteria cuts the sample down to 149 stars, and from these we report a success rate of 70% for finding stars with $\text{[Fe/H]}\le -2.5$ and 22% for finding stars with $\text{[Fe/H]}\le -3.0$. These statistics compare favourably with other surveys that search for extremely metal-poor stars, namely an improvement by a factor of $\sim 4-5$ for recovering stars with $\text{[Fe/H]}\le -3.0$. In addition, Pristine covers a fainter magnitude range than its predecessors, and can thus probe deeper into the Galactic halo.

14 pages, 6 figures, 4 tables, full version of Table 1 available on-line only, accepted for publication in MNRAS

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Cited by in corpus (10)

• The Pristine survey X: a large population of low-metallicity stars permeates the Galactic disk
• The Pristine survey VIII: The metallicity distribution function of the Milky Way halo down to the extremely metal-poor regime
• Pristine IX: CFHT ESPaDOnS Spectroscopic Analysis of 115 Bright Metal-Poor Candidate Stars
• The Pristine Inner Galaxy Survey (PIGS) II: Uncovering the most metal-poor populations in the inner Milky Way
• Observational constraints on the survival of pristine stars
• Stellar metallicities from SkyMapper photometry I: A study of the Tucana II ultra-faint dwarf galaxy
• The Pristine survey XIII: Uncovering the very metal-poor tail of the thin disc
• The Pristine survey -- VII. A cleaner view of the Galactic outer halo using blue horizontal branch stars
• The Pristine survey -- XV. A CFHT ESPaDOnS view on the Milky Way halo and disc populations
• The Pristine survey XIV: chemical analysis of two ultra-metal-poor stars