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Are Galactic globular cluster AGB stars rich or poor in Sodium? Sodium abundance of AGB and RGB stars in NGC 2808

Published online by Cambridge University Press:  31 March 2017

Yue Wang
Affiliation:
European Southern Observatory, Garching, Germany Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, China (email: [email protected])
Francesca Primas
Affiliation:
European Southern Observatory, Garching, Germany
Corinne Charbonnel
Affiliation:
Department of Astronomy, University of Geneva, Switzerland CNRS UMR 5277 IRAP & Université de Toulouse, France
Mathieu Van der Swaelmen
Affiliation:
Observatoire de la Côte d’Azur, CNRS UMR 7293, BP4229, Nice, France
William Chantereau
Affiliation:
Department of Astronomy, University of Geneva, Switzerland
Giuseppe Bono
Affiliation:
Dipartimento di Fisica, Universit á di Roma Tor Vergata, Rome, Italy
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Abstract

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A spectroscopic study comparing the [Na/Fe] distributions of RGB and AGB stars in the Galactic globular cluster (GC) NGC 6752 found that there was no Na-rich, 2nd-generation star along the early-AGB of this cluster. This came as a surprise since in this GC, as well as other Galactic GCs studied so far, 1st- and 2nd-generation stars have usually been found from the main sequence turnoff up to the red giant branch. To investigate whether the failure of a significant fraction of stars to ascend the AGB also happens to other GCs, we studied a sample of AGB and RGB stars in NGC 2808 observed at the ESO/VLT with FLAMES. Contrary to NGC 6752, we find that the AGB and RGB stars we studied in NGC 2808 have comparable [Na/Fe] dispersions.

Type
Contributed Papers
Copyright
Copyright © International Astronomical Union 2017 

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