Lagarde, N.; Reylé, C.; Robin, A. C.; Tautvaišienė, G.; Drazdauskas, A.; Mikolaitis, Š.; Minkevičiūtė, R.; Stonkutė, E.; Chorniy, Y.; Bagdonas, V.; Miglio, A.; Nasello, G.; Gilmore, G.; Randich, S.; Bensby, T.; Bragaglia, A.; Flaccomio, E.; Francois, P.; Korn, A. J.; Pancino, E.; Smiljanic, R.; Bayo, A.; Carraro, G.; Costado, M. T.; Jiménez-Esteban, F.; Jofré, P.; Martell, S. L.; Masseron, T.; Monaco, L.; Morbidelli, L.; Sbordone, L.; Sousa, S. G.; Zaggia, S.
Bibliographical reference
Astronomy and Astrophysics, Volume 621, id.A24, 11 pp.
Description
Context. The Gaia-ESO Public Spectroscopic Survey using FLAMES at the
VLT has obtained high-resolution UVES spectra for a large number of
giant stars, allowing a determination of the abundances of the key
chemical elements carbon and nitrogen at their surface. The surface
abundances of these chemical species are known to change in stars during
their evolution on the red giant branch (RGB) after the first dredge-up
episode, as a result of the extra mixing phenomena. Aims: We
investigate the effects of thermohaline mixing on C and N abundances
using the first comparison between the Gaia-ESO survey [C/N]
determinations with simulations of the observed fields using a model of
stellar population synthesis. Methods: We explore the effects of
thermohaline mixing on the chemical properties of giants through stellar
evolutionary models computed with the stellar evolution code STAREVOL.
We include these stellar evolution models in the Besançon Galaxy
model to simulate the [C/N] distributions determined from the UVES
spectra of the Gaia-ESO survey and to compare them with the
observations. Results: Theoretical predictions including the
effect of thermohaline mixing are in good agreement with the
observations. However, the field stars in the Gaia-ESO survey with C and
N abundance measurements have a metallicity close to solar, where the
efficiency of thermohaline mixing is not very large. The C and N
abundances derived by the Gaia-ESO survey in open and globular clusters
clearly show the impact of thermohaline mixing at low metallicity, which
explains the [C/N] value observed in lower mass and older giant stars.
Using independent observations of carbon isotopic ratio in clump field
stars and open clusters, we also confirm that thermohaline mixing should
be taken into account to explain the behaviour of
12C/13C as a function of stellar age.
Conclusions: Overall, the current model including thermohaline mixing is
able to reproduce very well the C and N abundances over the whole
metallicity range investigated by the Gaia-ESO survey data.
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