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The Pristine survey XI: the FORS2 sample

  • Caffau, E GEPI, Observatoire de Paris, Université PSL, CNRS, Place Jules Janssen, F-92190 Meudon, France
  • Bonifacio, P ORCID GEPI, Observatoire de Paris, Université PSL, CNRS, Place Jules Janssen, F-92190 Meudon, France
  • Sbordone, L European Southern Observatory, Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago, Chile
  • Matas Pinto, A M GEPI, Observatoire de Paris, Université PSL, CNRS, Place Jules Janssen, F-92190 Meudon, France
  • François, P GEPI, Observatoire de Paris, Université PSL, CNRS, 77 Av. Denfert-Rochereau, F-75014 Paris, France
  • Jablonka, P Institute of Physics, Laboratoire d’Astrophysique, Ecole Polytechnique Fédérale de Lausanne (EPFL), Observatoire de Sauverny, CH-1290 Versoix, Switzerland
  • Lardo, C ORCID Institute of Physics, Laboratoire d’Astrophysique, Ecole Polytechnique Fédérale de Lausanne (EPFL), Observatoire de Sauverny, CH-1290 Versoix, Switzerland
  • Martin, N F Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany
  • Starkenburg, E Leibniz Institute for Astrophysics Potsdam (AIP), An der Sternwarte 16, D-14482 Potsdam, Germany
  • Aguado, D Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
  • González-Hernández, J I Departamento de Astrofísica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain
  • Venn, K ORCID Department of Physics and Astronomy, University of Victoria, Victoria, BC V8W 3P2, Canada
  • Mashonkina, L Institute of Astronomy, Russian Academy of Sciences, RU-119017 Moscow, Russia
  • Sestito, F CNRS, Observatoire Astronomique de Strasbourg, Université de Strasbourg, UMR 7550, F-67000, France
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  • 2020-2-28
Published in:
  • Monthly Notices of the Royal Astronomical Society. - Oxford University Press (OUP). - 2020, vol. 493, no. 4, p. 4677-4691
Space and Planetary Science
Astronomy and Astrophysics
English Abstract
Extremely metal-poor (EMP) stars are old objects that mostly formed very early after the big bang. They are rare and, to select them, we have to rely on low-resolution spectroscopic or photometric surveys; specifically the combination of narrow- and broad-band photometry provides a powerful and time efficient way to select MP stars. The Pristine photometric survey is using the Canada–France–Hawaii Telescope MegaCam wide-field imager to obtain narrow-band photometry by utilizing a filter centred at 395.2 nm on the Ca ii-H and -K lines. Gaia DR 2 is providing us the wide-band photometry as well as parallaxes. Follow-up observations of MP candidates allowed us to improve our photometric calibrations. In this paper of the series we analyse MP stars observed with FORS2 at VLT. We demonstrate the Pristine calibration adopted in this work to be able to provide metallicities accurate to ±0.3 dex for MP giant stars with good parallaxes, while it performs poorly for dwarf and turn-off stars, whatever the accuracy on the parallaxes. We find some MP and very MP stars that are not enhanced in α elements. Such stars have already been found in several other searches, and a higher resolution follow-up of our sample would be useful to put our findings on a firmer ground. This sample of stars analysed has a low fraction of carbon-enhanced MP stars, regardless of the definition adopted. This deficiency could indicate a small sensitivity of the Pristine filter to carbon abundance, issue to be addressed in the future.
Language
  • English
Open access status
green
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https://folia.unifr.ch/global/documents/166682
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