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arXiv 1503.09085astro-ph.SR
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从恒星模型的g-模周期间隔的振荡揭示的红巨星核心附近的结构故障

Structural glitches near the cores of red giants revealed by oscillations in g-mode period spacings from stellar models

M. S. Cunha, D. Stello, P. P. Avelino, J. Christensen-Dalsgaard, R. H. D. Townsend

备注：
Accepted for publication in ApJ
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摘要：

随着星震学的最新进展，现在有可能窥视红巨星的核心，这可能提供一种方法来研究核燃烧和混合等过程，通过它们的印记作为恒星核心的急剧结构变化-故障。在这里，我们展示了这样的核心故障如何影响我们在红巨星中观察到的振荡。我们推导出一个分析表达式，描述了预期的频率模式中存在的毛刺。该公式还考虑了声波和重力波之间的耦合。从一个广泛的一组典型的恒星模型，我们发现毛刺引起的变化的周期间隔和惯性的非径向模式在几个阶段的红巨星演化。在功率谱和埃歇勒图等星震图中，模式振幅和频率模式的外观发生了重大变化。有趣的是，沿着红巨星分支，故障引起的变化只发生在光度凸起处，这可能提供了一个直接的地震指示器，指示处于特定演化阶段的恒星。同样，我们发现的变化，只有在某些后氦点火的演化阶段，即在早期阶段的氦核燃烧和氦壳燃烧的开始，标志着渐近巨星分支颠簸。根据我们的结果，我们注意到，假设恒星是无故障的，而他们不是，可能会导致一个错误的估计周期间隔。我们进一步注意到，包括扩散和混合超越经典史瓦西，可能会影响毛刺的特性，可能提供一种方法来研究这些物理过程。

英文摘要：

With recent advances in asteroseismology it is now possible to peer into the cores of red giants, potentially providing a way to study processes such as nuclear burning and mixing through their imprint as sharp structural variations -- glitches -- in the stellar cores. Here we show how such core glitches can affect the oscillations we observe in red giants. We derive an analytical expression describing the expected frequency pattern in the presence of a glitch. This formulation also accounts for the coupling between acoustic and gravity waves. From an extensive set of canonical stellar models we find glitch-induced variation in the period spacing and inertia of non-radial modes during several phases of red-giant evolution. Significant changes are seen in the appearance of mode amplitude and frequency patterns in asteroseismic diagrams such as the power spectrum and the échelle diagram. Interestingly, along the red-giant branch glitch-induced variation occurs only at the luminosity bump, potentially providing a direct seismic indicator of stars in that particular evolution stage. Similarly, we find the variation at only certain post-helium-ignition evolution stages, namely, in the early phases of helium-core burning and at the beginning of helium-shell burning signifying the asymptotic-giant-branch bump. Based on our results, we note that assuming stars to be glitch-free, while they are not, can result in an incorrect estimate of the period spacing. We further note that including diffusion and mixing beyond classical Schwarzschild, could affect the characteristics of the glitches, potentially providing a way to study these physical processes.

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