Pristine IX: CFHT ESPaDOnS Spectroscopic Analysis of 115 Bright Metal-Poor Candidate Stars

TL;DR

This study presents a detailed spectroscopic analysis of 115 bright metal-poor stars, discovering new extremely metal-poor stars, analyzing their chemical compositions, and exploring their kinematics to understand the Galaxy's early chemo-dynamics.

Contribution

It provides new high-resolution spectroscopic data for 115 stars, discovering 28 new stars with [Fe/H]<-2.5, and offers insights into their chemical and dynamical properties, enhancing understanding of the metal-poor Galaxy.

Findings

28 new stars with [Fe/H]<-2.5 discovered

Identification of a new r-process rich star and CEMP-s candidate

Some stars show unusual kinematics, including plunging orbits and association with Gaia-Enceladus

Abstract

A chemo-dynamical analysis of 115 metal-poor candidate stars selected from the narrow-band Pristine photometric survey is presented based on CFHT high-resolution ESPaDoNS spectroscopy. We have discover 28 new bright (V < 15) stars with [Fe/H]<-2.5 and 5 with [Fe/H]<-3.0 for success rates of 40% (28/70) and 19% (5/27), respectively. A detailed model atmospheres analysis is carried out for the 28 new metal-poor stars. Stellar parameters were determined from SDSS photometric colours, Gaia DR2 parallaxes, MESA/MIST stellar isochrones, and the initial Pristine survey metallicities, following a Bayesian inference method. Chemical abundances are determined for 10 elements (Na, Mg, Ca, Sc, Ti, Cr, Fe, Ni, Y, Ba). Most stars show chemical abundance patterns that are similar to the normal metal-poor stars in the Galactic halo; however, we also report the discoveries of a new r-process rich star, a new CEMP-s candidate with [Y/Ba]>0, and a metal-poor star with very low [Mg/Fe]. The kinematics and orbits for all of the highly probable metal-poor candidates are determined by combining our precision radial velocities with Gaia DR2 proper motions. Some stars show unusual kinematics for their chemistries, including planar orbits, unbound orbits, and highly elliptical orbits that plunge deeply into the Galactic bulge (Rperi < 0.5 kpc); also, eight stars have orbital energies and actions consistent with the Gaia-Enceladus accretion event. This paper contributes to our understanding of the complex chemo-dynamics of the metal-poor Galaxy, and increases the number of known bright metal-poor stars available for detailed nucleosynthetic studies.