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

Molaro, P.; Aguado, D. S.; Caffau, E.; Allende Prieto, C.; Bonifacio, P.; González Hernández, J. I.; Rebolo, R.; Zapatero Osorio, M. R.; Cristiani, S.; Pepe, F.; Santos, N. C.; Alibert, Y.; Cupani, G.; Di Marcantonio, P.; D'Odorico, V.; Lovis, C.; Martins, C. J. A. P.; Milaković, D.; Murphy, M. T.; Nunes, N. J.; Schmidt, T. M.; Sousa, S.; Sozzetti, A.; Suárez Mascareño, A.
Bibliographical reference

Astronomy and Astrophysics

Advertised on:
Number of authors
IAC number of authors
Refereed citations
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.
Related projects
spectrum of mercury lamp
Chemical Abundances in Stars
Stellar spectroscopy allows us to determine the properties and chemical compositions of stars. From this information for stars of different ages in the Milky Way, it is possible to reconstruct the chemical evolution of the Galaxy, as well as the origin of the elements heavier than boron, created mainly in stellar interiors. It is also possible to
Allende Prieto