The Pristine Survey -- VI. The first three years of medium-resolution follow-up spectroscopy of Pristine EMP star candidates

TL;DR

This paper reports on a three-year medium-resolution spectroscopic survey of Pristine EMP star candidates, identifying over 800 new very metal-poor stars and analyzing their carbon enhancement, thereby advancing the search for ancient stars.

Contribution

The study provides the first large-scale spectroscopic follow-up of Pristine survey candidates, significantly expanding the catalog of known EMP stars and refining success rates for identifying such stars.

Findings

Identified 707 new very metal-poor stars with [Fe/H] < -2.0.

Discovered 95 new extremely metal-poor stars with [Fe/H] < -3.0.

Reported high carbon enhancement fractions among the most metal-poor stars.

Abstract

We present the results of a 3-year long, medium-resolution spectroscopic campaign aimed at identifying very metal-poor stars from candidates selected with the CaHK, metallicity-sensitive Pristine survey. The catalogue consists of a total of 1007 stars, and includes 146 rediscoveries of metal-poor stars already presented in previous surveys, 707 new very metal-poor stars with [Fe/H] < -2.0, and 95 new extremely metal-poor stars with [Fe/H] < -3.0. We provide a spectroscopic [Fe/H] for every star in the catalogue, and [C/Fe] measurements for a subset of the stars (10% with [Fe/H] < -3 and 24% with -3 < [Fe/H] < -2) for which a carbon determination is possible, contingent mainly on the carbon abundance, effective temperature and S/N of the stellar spectra. We find an average carbon enhancement fraction ([C/Fe] >= +0.7) of 41 +- 4% for stars with -3 < [Fe/H] < -2 and 58 +- 14% for stars with [Fe/H] < -3, and report updated success rates for the Pristine survey of 56 % and 23 % to recover stars with [Fe/H] < -2.5 and [Fe/H] < -3, respectively. Finally, we discuss the current status of the survey and its preparation for providing targets to upcoming multi-object spectroscopic surveys such as WEAVE.