The <sup>12</sup>C/<sup>13</sup>C isotopic ratio at the dawn of chemical evolution - INSU - Institut national des sciences de l'Univers
Article Dans Une Revue Astronomy & Astrophysics Année : 2023

The 12C/13C isotopic ratio at the dawn of chemical evolution

P. Molaro
  • Fonction : Auteur
D. S. Aguado
  • Fonction : Auteur
C. Allende Prieto
  • Fonction : Auteur
J. I. González Hernández
  • Fonction : Auteur
R. Rebolo
  • Fonction : Auteur
M. R. Zapatero Osorio
  • Fonction : Auteur
S. Cristiani
  • Fonction : Auteur
F. Pepe
  • Fonction : Auteur
N. C. Santos
  • Fonction : Auteur
Y. Alibert
  • Fonction : Auteur
G. Cupani
  • Fonction : Auteur
P. Di Marcantonio
  • Fonction : Auteur
V. d'Odorico
  • Fonction : Auteur
C. Lovis
  • Fonction : Auteur
C. J. A. P. Martins
  • Fonction : Auteur
D. Milaković
  • Fonction : Auteur
M. T. Murphy
  • Fonction : Auteur
N. J. Nunes
  • Fonction : Auteur
T. M. Schmidt
  • Fonction : Auteur
S. Sousa
  • Fonction : Auteur
A. Sozzetti
  • Fonction : Auteur
A. Suárez Mascareño
  • Fonction : Auteur

Résumé

Context. The known mega metal-poor (MMP) and hyper metal-poor (HMP) stars, with [Fe/H] < −6.0 and < −5.0, respectively, likely belong to the CEMP-no class, namely, carbon-enhanced stars with little or no second peak neutron-capture elements. They are likely second-generation stars, and the few elements measurable in their atmospheres are used to infer the properties of a single or very few progenitors.
Aims: The high carbon abundance in the CEMP-no stars offers a unique opportunity to measure the carbon isotopic ratio, which directly indicates the presence of mixing between the He- and H-burning layers either within the star or in the progenitor(s). By means of high-resolution spectra acquired with the ESPRESSO spectrograph at the VLT, we aim to derive values for the 12C/13C ratio at the lowest metallicities.
Methods: We used a spectral synthesis technique based on the SYNTHE code and on ATLAS models within a Markov chain Monte Carlo methodology to derive 12C/13C in the stellar atmospheres of four of the most metal-poor stars known: the MMP giant SMSS J0313-6708 ([Fe/H] < −7.1), the HMP dwarf HE 1327-2326 ([Fe/H] = −5.8), the HMP giant SDSS J1313-0019 ([Fe/H] = −5.0), and the ultra metal-poor subgiant HE0233 -0343 ([Fe/H] = −4.7). We also revised a previous value for the MMP giant SMSS J1605-1443 ([Fe/H] = −6.2).
Results: In four stars we derive an isotopic value while for HE 1327-2326 we provide a lower limit. All measurements are in the range 39 < 12C/13C < 100, showing that the He- and H-burning layers underwent partial mixing either in the stars or, more likely, in their progenitors. This provides evidence of a primary production of 13C at the dawn of chemical evolution. CEMP-no dwarf stars with slightly higher metallicities show lower isotopic values, <30 and even approaching the CNO cycle equilibrium value. Thus, extant data suggest the presence of a discontinuity in the 12C/13C ratio at around [Fe/H] ≈ − 4, which could mark a real difference between the progenitor pollution captured by stars with different metallicities. We also note that some MMP and HMP stars with high 12C/13C show low 7Li values, providing an indication that mixing in the CEMP-no progenitors is not responsible for the observed Li depletion.
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insu-04848712 , version 1 (19-12-2024)

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P. Molaro, D. S. Aguado, E. Caffau, C. Allende Prieto, P. Bonifacio, et al.. The 12C/13C isotopic ratio at the dawn of chemical evolution. Astronomy & Astrophysics, 2023, 679, ⟨10.1051/0004-6361/202347676⟩. ⟨insu-04848712⟩
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