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Uncertainties on near-core mixing in red-clump stars: effects on the period spacing and on the luminosity of the AGB bump

Journal
Date Issued
2015
Author(s)
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Salaris, Maurizio
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Montalbán, Josefina
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BRESSAN, Alessandro
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Noels, Arlette
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DOI
Description
AM acknowledges the support of the UK Science and Technology Facilities Council (STFC). Funding for the Stellar Astrophysics Centre is provided by The Danish National Research Foundation (Grant agreement no.: DNRF106). The research leading to these results has received funding from the European Community's Seventh Framework Programme ([FP7/2007-2013]) under grant agreement no. 312844 (SPACEINN). AM and LG acknowledge support from PRIN INAF 2014 (PI: L. Girardi) – CRA 1.05.01.94.05. SC is funded by PRIN-INAF 2014 (PI: S. Cassisi) and by the Economy and Competitiveness Ministry of the Kingdom of Spain (Grant AYA2013-42781P). JM and PM acknowledge the support from the ERC Consolidator Grant funding scheme ( project STARKEY , G.A. n. 615604). AB acknowledges support from PRIN INAF 2014 ‘Star formation and evolution in galactic nuclei’.
Abstract
Low-mass stars in the He-core-burning (HeCB) phase play a major role in stellar, galactic, and extragalactic astrophysics. The ability to predict accurately the properties of these stars, however, depends on our understanding of convection, which remains one of the key open questions in stellar modelling. We argue that the combination of the luminosity of the AGB bump (AGBb) and the period spacing of gravity modes (∆Π1) during the HeCB phase provides us with a decisive test to discriminate between competing models of these stars. We use the Modules for Experiments in Stellar Astrophysics (MESA), a Bag of Stellar Tracks and Isochrones (BaSTI), and PAdova & TRieste Stellar Evolution Code (PARSEC) stellar evolution codes to model a typical giant star observed by Kepler. We explore how various near-core-mixing scenarios affect the predictions of the above-mentioned constraints, and we find that ∆Π1 depends strongly on the prescription adopted. Moreover we show that the detailed behaviour of ∆Π1 shows the signature of sharp variations in the Brunt-Väisälä frequency, which could potentially give additional information about near-core features. We find evidence for the AGBb among Kepler targets, and a first comparison with observations shows that, even if standard models are able to reproduce the luminosity distribution, no standard model can account for satisfactorily the period spacing of HeCB stars. Our analysis allows us to outline a candidate model to describe simultaneously the two observed distributions: a model with a moderate overshooting region characterized by an adiabatic thermal stratification. This prescription will be tested in the future on cluster stars, to limit possible observational biases.
Volume
453
Issue
3
Start page
2290
Uri
Url
Issn Identifier
0035-8711
Ads BibCode
2015MNRAS.453.2290B
Rights
open.access
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