The Pristine survey – XX. GTC follow-up observations of extremely metal-poor stars identified from Pristine and LAMOST

Author:

Arentsen Anke12ORCID,Aguado David S34,Sestito Federico5ORCID,González Hernández Jonay I67,Martin Nicolas F28ORCID,Starkenburg Else9,Jablonka Pascale1011,Yuan Zhen2ORCID

Affiliation:

1. Institute of Astronomy, University of Cambridge , Madingley Road, Cambridge CB3 0HA, UK

2. Observatoire Astronomique de Strasbourg, Université de Strasbourg, CNRS, UMR 7550 , F-67000 Strasbourg, France

3. Dipartimento di Fisica e Astronomia, Universitá degli Studi di Firenze , Via G. Sansone 1, I-50019 Sesto Fiorentino, Italy

4. INAF – Osservatorio Astrofisico di Arcetri , Largo E. Fermi 5, I-50125 Firenze, Italy

5. Department of Physics and Astronomy, University of Victoria , PO Box 3055, STN CSC, Victoria, BC V8W 3P6, Canada

6. Instituto de Astrofísica de Canarias , E-38205 La Laguna, Tenerife, Spain

7. Departamento de Astrofísica, Universidad de La Laguna , E-38206 La Laguna, Tenerife, Spain

8. Max-Planck-Institut für Astronomie , Königstuhl 17, D-69117 Heidelberg, Germany

9. Kapteyn Astronomical Institute, University of Groningen , Postbus 800, NL-9700 AV Groningen, the Netherlands

10. Laboratoire d’astrophysique, École Polytechnique Fédérale de Lausanne (EPFL), Observatoire , CH-1290 Versoix, Switzerland

11. GEPI, Observatoire de Paris, Université PSL, CNRS , Place Jules Janssen, F-92195 Meudon, France

Abstract

ABSTRACT Ultra-metal-poor stars ($\rm {[Fe/H]} \lt -4.0$) are very rare, and finding them is a challenging task. Both narrow-band photometry and low-resolution spectroscopy have been useful tools for identifying candidates, and in this work, we combine both approaches. We cross-matched metallicity-sensitive photometry from the Pristine survey with the low-resolution spectroscopic Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) data base, and re-analysed all LAMOST spectra with $\rm {[Fe/H]} _{\rm Pristine} \lt -2.5$. We find that ∼1/3rd of this sample (selected without $\rm {[Fe/H]} _{\rm Pristine}$ quality cuts) also have spectroscopic $\rm {[Fe/H]} \lt -2.5$. From this sample, containing many low signal-to-noise ratio (S/N) spectra, we selected 11 stars potentially having $\rm {[Fe/H]} \lt -4.0$ or $\rm {[Fe/H]} \lt -3.0$ with very high carbon abundances, and we performed higher S/N medium-resolution spectroscopic follow-up with the Optical System for Imaging and low Resolution Integrated Spectroscopy (OSIRIS) on the 10.4-m Gran Telescopio Canarias (GTC). We confirm their extremely low metallicities, with a mean of $\rm {[Fe/H]} = -3.4$, and the most metal-poor star having $\rm {[Fe/H]} = -3.8$. Three of these are clearly carbon-enhanced metal-poor (CEMP) stars with $+1.65 \lt \rm {[C/Fe]} \lt +2.45$. The two most carbon-rich stars are either among the most metal-poor CEMP-s stars or the most carbon-rich CEMP-no stars known, the third is likely a CEMP-no star. We derived orbital properties for the OSIRIS sample and find that only one of our targets can be confidently associated with known substructures/accretion events, and that three out of four inner halo stars have prograde orbits. Large spectroscopic surveys may contain many hidden extremely and ultra-metal-poor stars, and adding additional information from e.g. photometry as in this work can uncover them more efficiently and confidently.

Funder

European Research Council

Horizon 2020 Framework Programme

University of Cambridge

Fitzwilliam College

Isaac Newton Trust

University of Victoria

Spanish Ministry of Science and Innovation

MICINN

French National Research Agency

INSU,CNRS

CNRS

Dutch Research Council

Swiss National Science Foundation

Publisher

Oxford University Press (OUP)

Subject

Space and Planetary Science,Astronomy and Astrophysics

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