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Multiple populations along the asymptotic giant branch of the globular cluster M 4

Lardo, C and Salaris, M and Savino, A and Donati, P and Stetson, PB and Cassisi, S (2017) Multiple populations along the asymptotic giant branch of the globular cluster M 4. Monthly Notices of the Royal Astronomical Society, 466 (3). pp. 3507-3512. ISSN 0035-8711

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Abstract

Nearly all Galactic globular clusters host stars that display characteristic abundance anti-correlations, like the O-rich/Na-poor pattern typical of field halo stars, together with O-poor/Na-rich additional components. A recent spectroscopic investigation questioned the presence of O-poor/Na-rich stars amongst a sample of asymptotic giant branch stars in the cluster M 4, at variance with the spectroscopic detection of a O-poor/Na-rich component along both the cluster red giant branch and horizontal branch. This is contrary to what is expected from the cluster horizontal branch morphology and horizontal branch stellar evolution models. Here we have investigated this issue by employing the CUBI= (U-B)-(B-I) index, that previous studies have demonstrated to be very effective in separating multiple populations along both the red giant and asymptotic giant branch sequences. We confirm previous results that the RGB is intrinsically broad in the V-CUBI diagram, with the presence of two components which nicely correspond to the two populations identified by high-resolution spectroscopy. We find that AGB stars are distributed over a wide range of CUBI values, in close analogy with what is observed for the RGB, demonstrating that the AGB of M4 also hosts multiple stellar populations.

Item Type: Article
Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Uncontrolled Keywords: astro-ph.SR; astro-ph.SR; astro-ph.GA
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: Oxford University Press
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Date Deposited: 09 Jan 2017 12:01
Last Modified: 08 Sep 2017 14:47
DOI or Identification number: 10.1093/mnras/stw3374
URI: http://researchonline.ljmu.ac.uk/id/eprint/5203

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