论文标题
表征AGB颠簸及其在恒星内部限制混合过程的潜力
Characterising the AGB bump and its potential to constrain mixing processes in stellar interiors
论文作者
论文摘要
在90年代，鉴于其发光度和恒星金属性之间的依赖性较弱，理论研究促使使用渐近巨型分支凸起（AGBB）作为标准蜡烛。由于观察到的渐近巨型分支（AGB）样品的大小很小，因此检测AGBB并不是一件容易的事。但是，由于Corot，Kepler和Tess Space-Borne任务收集的大量数据，现在可能是可能的。众所周知，AGB凹凸提供了有关低质量恒星内部结构的有价值信息，尤其是在混合过程中，例如在核心HE燃烧阶段的核心过冲弹药等过程中。在这种情况下，我们分析了Kepler和Tess观察到的约4,000个进化的巨头，包括红色巨型分支星和AGB恒星，为此，可以使用瓜糖酶和光谱数据。通过使用统计混合模型，我们在最大振荡能力和有效温度下都检测到AGBB的频率。然后，我们将模块用于恒星天体物理学中的实验台面恒星进化代码来对AGB星星进行建模，并与AGBB的发生与观察结果相匹配。从观察结果中，我们可以在15块质量和金属性中得出AGBB位置。我们注意到，质量越高，AGBB出现在进化轨道中，这与理论工作一致。此外，当金属性增加时，我们发现AGBB处的光度略有增加，这使使用AGBB作为标准蜡烛的使用变得复杂。通过将这些观察结果与恒星模型拟合，我们注意到低质量星（M <1.0 $ m _ {\ odot} $）需要一个在核心He燃烧阶段的小核心过冲的区域。这种核心过度范围向高质量增加，但高于m> 1.5 $ m _ {\ odot} $，我们发现AGBB位置不能单独使用逼真的He-core过度旋转来复制，而必须调用其他混合过程。
In the 90's, theoretical studies motivated the use of the asymptotic-giant branch bump (AGBb) as a standard candle given the weak dependence between its luminosity and stellar metallicity. Because of the small size of observed asymptotic-giant branch (AGB) samples, detecting the AGBb is not an easy task. However, this is now possible thanks to the wealth of data collected by the CoRoT, Kepler, and TESS space-borne missions. It is well-know that the AGB bump provides valuable information on the internal structure of low-mass stars, particularly on mixing processes such as core overshooting during the core He-burning phase. In this context, we analysed ~ 4,000 evolved giants observed by Kepler and TESS, including red-giant branch stars and AGB stars, for which asteroseismic and spectrometric data are available. By using statistical mixture models, we detected the AGBb both in frequency at maximum oscillation power and in effective temperature. Then, we used the Modules for Experiments in Stellar Astrophysics MESA stellar evolution code to model AGB stars and match the AGBb occurrence with observations. From observations, we could derive the AGBb location in 15 bins of mass and metallicity. We noted that the higher the mass, the later the AGBb occurs in the evolutionary track, which agrees with theoretical works. Moreover, we found a slight increase of the luminosity at the AGBb when the metallicity increases, which complicates the use of the AGBb as a standard candle. By fitting those observations with stellar models, we noticed that low-mass stars (M < 1.0 $M_{\odot}$) require a small core overshooting region during the core He-burning phase. This core overshooting extent increases toward high mass, but above M > 1.5 $M_{\odot}$ we found that the AGBb location cannot be reproduced with a realistic He-core overshooting alone, and instead additional mixing processes have to be invoked.
