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Carbon stars within the Gaia-ESO survey

Published online by Cambridge University Press:  17 July 2015

C. Abia
Affiliation:
Dpto. Física Teórica y del Cosmos, Universidad de Granada, 18071 Granada, Spain
S. Van Eck
Affiliation:
Institut d'Astronomie et Astrophysique, CP. 226, Université Libre de Bruxelles, Boulevard du Triomphe, 1050 Bruxelles, Belgium
T. Masseron
Affiliation:
Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
T. Merle
Affiliation:
Institut d'Astronomie et Astrophysique, CP. 226, Université Libre de Bruxelles, Boulevard du Triomphe, 1050 Bruxelles, Belgium
C.C. Worley
Affiliation:
Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
T. Zwitter
Affiliation:
Faculty of Mathematics and Physics, University of Ljubljana, Ljubljana, Slovenia
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Abstract

The overwhelming majority of the astronomical objects are oxygen-rich, showing an abundance ratio C/O < 1 (by number). The so-called intrinsic carbon stars (C/O > 1) are formed during the AGB phase evolution of 1.5 ≤ M/M≤ 3 stars through the mixing of fresh 12C from the interior of the star into the envelope during the 3rd dredge-up after each thermal pulse. They commonly show s-element enhancements produced by slow neutron captures provided by the 13C(α,n)16O reaction. The prototype of these stars are the AGB C-stars. Extrinsic carbon stars on the other hand, are formed in binary systems by mass transfer of carbon rich material from a former AGB star (now a white dwarf) onto the secondary star. Prototype of these class are the CH stars. A zoo of carbon-rich type stars exists, all being tracers of intermediate-age stellar populations. These stars are extremely useful for studies of the star formation history and chemical evolution of the galaxies. We present the detection and chemical analysis of carbon-enriched stars so far discovered within the Gaia-ESO survey. C-enriched candidates are identified from the analysis of a series of enhanced molecular features, measured through photometric and narrow-band spectroscopic filters. Then, the stellar parameters, C/O ratios and s-process element abundances are determined. The nature (intrinsic or extrinsic) of these carbon-enriched stars is discussed together with the expected impact of the Gaia mission on the knowledge of these objects in the Milky Way.

Type
Research Article
Copyright
© EAS, EDP Sciences, 2015

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