Constraining mixing processes in stellar cores using asteroseismology Impact of semiconvection in low-mass stars
Constraining mixing processes in stellar cores using asteroseismology Impact of semiconvection in low-mass stars
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DOI：
10.1051/0004-6361/201015847
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发表时间：
2011-05-01
影响因子：
6.5
通讯作者：
Weiss, A.
中科院分区：
文献类型：
--
作者：
Aguirre, V. Silva;Ballot, J.;Weiss, A.
上下文低质量恒星的整体演化很大程度上受到恒星内部过程的影响。特别是，对流不稳定区和过冲区的混合过程会影响观测值和主序列寿命。我们的目的是研究不同的对流边界定义和混合处方在低质量恒星的对流核心的影响，并区分的存在，大小和演化阶段的中央混合区通过星震学。我们实现了勒杜标准对流在我们的恒星演化代码，随着时间的推移扩散的方法混合的元素时，对流区存在。我们比较了模型的质量范围从1.1 M-圆点到2 M-圆点计算与两个不同的标准对流边界的定义，包括不同的混合处方内和超出正式限制的对流区域。通过计算大量模型的绝热振荡频率，我们根据罗克斯堡和沃龙佐夫（2003，A&A，411，215）定义的小间距与大间距的比值r（01）和r（10），仅使用l = 0和l = 1模式进行了星震诊断。分析了该地震仪器在主层序演化过程中对星星中心条件的敏感性。地震变量r（01）和r（10）在预期的可观测频率范围内几乎是线性的，我们表明，它们的斜率同时取决于中心的氢含量，对流核的范围，以及在核心边界的声速不连续的振幅。通过考虑约25种模式和准确度的频率测定预期从CoRoT和开普勒任务，我们提出的技术使我们能够检测到对流核心的存在，并区分不同大小的均匀混合的中心区域，而不需要一个强大的先验知识的恒星质量。
Context. The overall evolution of low-mass stars is heavily influenced by the processes occurring in the stellar interior. In particular, mixing processes in convectively unstable zones and overshooting regions affect the resulting observables and main sequence lifetime.Aims. We aim to study the effects of different convective boundary definitions and mixing prescriptions in convective cores of low-mass stars and to distinguish the existence, size, and evolutionary stage of the central mixed zone by means of asteroseismology.Methods. We implemented the Ledoux criterion for convection in our stellar evolution code, together with a time-dependent diffusive approach for mixing of elements when semiconvective zones are present. We compared models with masses ranging from 1.1 M-circle dot to 2 M-circle dot computed with two different criteria for convective boundary definition and included different mixing prescriptions within and beyond the formal limits of the convective regions. Using calculations of adiabatic oscillations frequencies for a large set of models, we developed an asteroseismic diagnosis using only l = 0 and l = 1 modes based on the ratios of small to large separations r(01) and r(10) defined by Roxburgh & Vorontsov (2003, A&A, 411, 215). We analyzed the sensitivity of this seismic tool to the central conditions of the star during the main sequence evolution.Results. The seismic variables r(01) and r(10) are almost linear in the expected observable frequency range, and we show that their slope depends simultaneously on the central hydrogen content, the extent of the convective core, and the amplitude of the sound-speed discontinuity at the core boundary. By considering about 25 modes and an accuracy in the frequency determinations as expected from the CoRoT and Kepler missions, the technique we propose allows us to detect the presence of a convective core and to discriminate the different sizes of the homogeneously mixed central region without the need for a strong prior knowledge on the stellar mass.