The Pristine survey – XII. Gemini-GRACES chemo-dynamical study of newly discovered extremely metal-poor stars in the Galaxy - Université PSL (Paris Sciences & Lettres) Accéder directement au contenu
Article Dans Une Revue Monthly Notices of the Royal Astronomical Society Année : 2021

The Pristine survey – XII. Gemini-GRACES chemo-dynamical study of newly discovered extremely metal-poor stars in the Galaxy

Collin Kielty
Kim Venn
Else Starkenburg
  • Fonction : Auteur
Nicolas Martin
David Aguado
Anke Arentsen
Sébastien Fabbro
Jonay González hernández
  • Fonction : Auteur
Carmela Lardo
Lyudmila Mashonkina
Julio Navarro
  • Fonction : Auteur
Chris Sneden
  • Fonction : Auteur
Guillaume Thomas
Kris Youakim
Spencer Bialek
  • Fonction : Auteur
Rubén Sánchez-Janssen

Résumé

High-resolution optical spectra of 30 metal-poor stars selected from the Pristine survey are presented, based on observations taken with the Gemini Observatory GRACES spectrograph. Stellar parameters Teff and log g are determined using a Gaia DR2 colour–temperature calibration and surface gravity from the Stefan–Boltzmann equation. GRACES spectra are used to determine chemical abundances (or upper limits) for 20 elements (Li, O, Na, Mg, K, Ca, Ti, Sc, Cr, Mn, Fe, Ni, Cu, Zn, Y, Zr, Ba, La, Nd, Eu). These stars are confirmed to be metal-poor ([Fe/H] < −2.5), with higher precision than from earlier medium-resolution analyses. The chemistry for most targets is similar to other extremely metal-poor stars in the Galactic halo. Three stars near [Fe/H] = −3.0 have unusually low Ca and high Mg, suggestive of contributions from few SN II where alpha-element formation through hydrostatic nucleosynthesis was more efficient. Three new carbon-enhanced metal-poor (CEMP) stars are also identified (two CEMP-s and one potential CEMP-no star) when our chemical abundances are combined with carbon from previous medium-resolution analyses. The GRACES spectra also provide precision radial velocities (σRV ≤ 0.2 km s−1) for dynamical orbit calculations with the Gaia DR2 proper motions. Most of our targets are dynamically associated with the Galactic halo; however, five stars with [Fe/H] < −3 have planar-like orbits, including one retrograde star. Another five stars are dynamically consistent with the Gaia-Sequoia accretion event; three have typical halo [α/Fe] ratios for their metallicities, whereas two are [Mg/Fe]-deficient, and one is a new CEMP-s candidate. These results are discussed in terms of the formation and early chemical evolution of the Galaxy.
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hal-03337609 , version 1 (06-08-2022)

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Collin Kielty, Kim Venn, Federico Sestito, Else Starkenburg, Nicolas Martin, et al.. The Pristine survey – XII. Gemini-GRACES chemo-dynamical study of newly discovered extremely metal-poor stars in the Galaxy. Monthly Notices of the Royal Astronomical Society, 2021, 506 (1), pp.1438-1461. ⟨10.1093/mnras/stab1783⟩. ⟨hal-03337609⟩
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