发表机构
Heidelberg Institute for Theoretical Studies (HITS) gGmbH（海德堡理论研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
该研究揭示了恒星演化中光度隆起起始的物理机制，指出平均分子量不连续面处比熵差的减小是触发隆起的核心原因。
AI 中文摘要
在演化过程中，恒星在光度-温度空间中遵循一条独特的路径。核心中氢已耗尽的低质量恒星沿着所谓的红巨星分支演化，该分支主要朝向光度增加和表面温度降低的方向。光度隆起是相对于这一总体增加趋势的暂时性光度下降。隆起在观测和恒星演化模型中均存在。然而，当模型中包含经典物理时，计算出的演化轨迹中的隆起出现在比观测到的隆起更高的光度处。为了理解为什么模型中的隆起比观测中出现得更晚，需要揭示隆起的物理机制。隆起的终点已被很好地理解；然而，隆起的起始仍然是一个谜。在此，我们报告了光度隆起起始的物理起源。我们表明，由于平均分子量不连续面向内移动，其处的比熵差减小。这种减小归因于在更小半径处温度与压力之比的降低。当达到临界值时，平均分子量不连续面处的比熵差充分减小，从而降低对流包层中的比熵。后者是隆起的关键特征。因此，平均分子量不连续面处比熵的演化为隆起的起始提供了可行的描述。
英文摘要
During their evolution, stars follow a distinct path in luminosity--temperature space. Low-mass stars that have exhausted hydrogen in their core follow the so-called red-giant branch which is predominantly in the direction of increasing luminosity and decreasing surface temperature. The luminosity bump is a temporary decrease in luminosity against this otherwise increasing trend. The bump is present in both observations and stellar evolution models. However, with canonical physics included in the models, the bump in computed evolutionary tracks appears at higher luminosities than the observed bump. To understand why the bump appears later in the models than in observations, the physics of the bump needs to be unravelled. The end point of the bump is well-understood; however, the onset of the bump is still an enigma. Here, we report on the physical origin of the onset of the luminosity bump. We show that the difference in specific entropy at the mean molecular weight discontinuity decreases due to the discontinuity moving in. This decrease is attributed to the decrease in the ratio of the temperature to the pressure at smaller radii. Upon reaching a critical value the specific entropy difference at the mean molecular weight discontinuity is reduced sufficiently to reduce the specific entropy in the convective envelope. The latter is a key signature of the bump. Hence the evolution of the specific entropy at the mean molecular weight discontinuity provides a viable description for the onset of the bump.
CommentsAccepted for publication by ApJL
