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The Gaia-ESO Survey : Impact of extra mixing on C and N abundances of giant stars

Lagarde, N.; Reylé, C.; Robin, A. C.; Tautvaišiene, G.; Drazdauskas, A.; Mikolaitis, S.; Minkevičiute, R.; Stonkute, E. LU ; Chorniy, Y. and Bagdonas, V., et al. (2019) In Astronomy and Astrophysics 621.
Abstract

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... (More)

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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keywords
Galaxy: Abundances, Galaxy: stellar content, Stars: Abundances, Stars: evolution
in
Astronomy and Astrophysics
volume
621
publisher
EDP Sciences
external identifiers
  • scopus:85059475072
ISSN
0004-6361
DOI
10.1051/0004-6361/201732433
language
English
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yes
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fbb9e54a-626e-4c95-931f-5eb86f81e12e
date added to LUP
2019-01-22 09:37:08
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2019-02-10 05:11:55
@article{fbb9e54a-626e-4c95-931f-5eb86f81e12e,
  abstract     = {<p>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 <sup>12</sup>C/<sup>13</sup>C 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.</p>},
  articleno    = {A24},
  author       = {Lagarde, N. and Reylé, C. and Robin, A. C. and Tautvaišiene, G. and Drazdauskas, A. and Mikolaitis, S. and Minkevičiute, R. and Stonkute, E. and Chorniy, Y. and Bagdonas, V. and Miglio, A. and Nasello, G. and Gilmore, G. and Randich, S. and Bensby, T. and Bragaglia, A. and Flaccomio, E. and Francois, P. and Korn, A. J. and Pancino, E. and Smiljanic, R. and Bayo, A. and Carraro, G. and Costado, M. T. and Jiménez-Esteban, F. and Jofré, P. and Martell, S. L. and Masseron, T. and Monaco, L. and Morbidelli, L. and Sbordone, L. and Sousa, S. G. and Zaggia, S.},
  issn         = {0004-6361},
  keyword      = {Galaxy: Abundances,Galaxy: stellar content,Stars: Abundances,Stars: evolution},
  language     = {eng},
  month        = {01},
  publisher    = {EDP Sciences},
  series       = {Astronomy and Astrophysics},
  title        = {The Gaia-ESO Survey : Impact of extra mixing on C and N abundances of giant stars},
  url          = {http://dx.doi.org/10.1051/0004-6361/201732433},
  volume       = {621},
  year         = {2019},
}