Uncertainties on near-core mixing in red-clump stars: effects on the period spacing and on the luminosity of the AGB bump
Uncertainties on near-core mixing in red-clump stars: effects on the period spacing and on the luminosity of the AGB bump
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DOI：
10.1093/mnras/stv1738
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发表时间：
2015-11-01
影响因子：
4.8
通讯作者：
Marigo, Paola
中科院分区：
文献类型：
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作者：
Bossini, Diego;Miglio, Andrea;Marigo, Paola
处于氦核燃烧（HeCB）阶段的低质量恒星在恒星、银河系和河外天体物理学中扮演着重要角色。然而，准确预测这些恒星性质的能力取决于我们对对流的理解，对流仍然是恒星建模中的关键开放问题之一。我们认为，在HeCB阶段，AGB凸点（AGBb）的光度和重力模式的周期间隔（Δ Pi（1））的组合为我们提供了一个决定性的测试，以区分这些恒星的竞争模型。我们使用恒星天体物理学实验模块（梅萨）、恒星轨道和等时线包（巴斯蒂）和Padova&TRieste恒星演化代码（PARSEC）对开普勒观测到的一颗典型的巨型星星进行了模拟。我们探讨了各种近核混合场景如何影响上述约束的预测，我们发现Delta Pi（1）强烈依赖于所采用的处方。此外，我们还表明，Delta Pi（1）的详细行为显示了Brunt-Vaisala频率急剧变化的特征，这可能会提供有关近核特征的更多信息。我们发现的AGBb开普勒目标之间的证据，并与观测结果的第一次比较表明，即使标准模型能够重现的光度分布，没有标准模型可以令人满意的HeCB星的周期间隔。我们的分析使我们能够勾勒出一个候选模型来描述同时观察到的两个分布：一个模型与一个温和的过冲区域，其特征在于绝热热分层。这一处方将在未来的星团恒星上进行测试，以限制可能的观测偏差。
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 (Delta Pi(1)) 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 EvolutionCode (PARSEC) stellar evolution codes to model a typical giant star observed by Kepler. We explore how various near-coremixing scenarios affect the predictions of the above-mentioned constraints, and we find that Delta Pi(1) depends strongly on the prescription adopted. Moreover we show that the detailed behaviour of Delta Pi(1) shows the signature of sharp variations in the Brunt-Vaisala 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.