镜像原理与红巨星碰撞：低质量恒星中的熵之战
Mirror principle and the red-giant bump: the battle of entropy in low-mass stars
摘要：
低质量恒星演化为红巨星的过程仍然知之甚少。在这个演化过程中，恒星的核心收缩，同时，外壳膨胀--这一过程被称为“镜子”。此外，有一个短暂的阶段，其中增加光度的趋势被逆转。这被称为红巨星分支碰撞。我们通过考虑恒星中特定的熵分布及其随时间的变化来探索这两种现象的潜在物理原因。我们发现，在光度最大和光度最小的凸块之间没有镜子，恒星是完全收缩的。当燃烧氢的壳层达到平均分子量不连续点时，收缩停止，恒星重新获得镜像。这标志着凹凸的亮度最小值。
英文摘要：
The evolution of low-mass stars into red giants is still poorly understood. During this evolution the core of the star contracts and, simultaneously, the envelope expands -- a process known as the `mirror'. Additionally, there is a short phase where the trend for increasing luminosity is reversed. This is known as the red-giant-branch bump. We explore the underlying physical reasons for these two phenomena by considering the specific entropy distribution in the star and its temporal changes. We find that between the luminosity maximum and luminosity minimum of the bump there is no mirror present and the star is fully contracting. The contraction is halted and the star regains its mirror when the hydrogen-burning shell reaches the mean molecular weight discontinuity. This marks the luminosity minimum of the bump.
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