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Kepler red-clump stars in the field and in open clusters: Constraints on core mixing

Bossini, D, Miglio, A, Salaris, M, Vrard, M, Cassisi, S, Mosser, B, Montalban, J, Girardi, L, Noels, A, Bressan, A, Pietrinferni, A and Tayar, J (2017) Kepler red-clump stars in the field and in open clusters: Constraints on core mixing. Monthly Notices of the Royal Astronomical Society, 469 (4). pp. 4718-4725. ISSN 0035-8711

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Abstract

Convective mixing in helium-core-burning (HeCB) stars is one of the outstanding issues in stellar modelling. The precise asteroseismic measurements of gravity-mode period spacing (&dela;σ1) have opened the door to detailed studies of the near-core structure of such stars, which had not been possible before. Here, we provide stringent tests of various core-mixing scenarios against the largely unbiased population of red-clump stars belonging to the old-open clusters monitored by Kepler, and by coupling the updated precise inference on &dela;σ1 in thousands of field stars with spectroscopic constraints. We find that models with moderate overshooting successfully reproduce the range observed of &dela;σ1 in clusters. In particular, we show that there is no evidence for the need to extend the size of the adiabatically stratified core, at least at the beginning of the HeCB phase. This conclusion is based primarily on ensemble studies of &dela;σ1 as a function of mass and metallicity. While &dela;σ1 shows no appreciable dependence on the mass, we have found a clear dependence of &dela;σ1 on metallicity, which is also supported by predictions from models.

Item Type: Article
Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2017 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Uncontrolled Keywords: 0201 Astronomical and Space Sciences
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: Oxford University Press
Date Deposited: 29 Jun 2020 10:26
Last Modified: 29 Jun 2020 10:30
DOI or Identification number: 10.1093/mnras/stx1135
URI: http://researchonline.ljmu.ac.uk/id/eprint/13205

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