澳大利亚国立大学Claudia Reyes团队揭示了M67星团恒星的声学模式追踪到对流包层的加深。2025年4月2日出版的《自然》杂志发表了这项成果。

恒星中的声振荡对恒星内部很敏感。泛音模式之间的频率差异（大间距）探测恒星密度，而低阶模式之间的差异（小间距）探测主序星类太阳恒星能量产生核心的声速梯度，从而探测它们的年龄。在恒星演化的后期阶段，以惰性核心为特征，小间距被认为会失去探测深部内部的大部分能力，并与大间距成正比。

研究组提出了证据，表明随着恒星从亚巨星阶段演变为红巨星，对流区迅速演变。通过测量疏散星团M67中27颗恒星的声振荡，他们观察到小间距和大间距之间的比例偏差，这是由对流包层底部的影响引起的。当对流包层在次巨星和红巨星演化过程中深入恒星时，这些偏差变得明显，最终进入超深区域，导致红巨星分支光度隆起。

星团恒星的紧密序列，在年龄和基本性质上没有大的扩展，对于揭示观测到的小间距与对流包层底部发生的化学不连续性之间的联系至关重要。研究组使用这个序列来证明，在主序星之后，结合大间距和小间距可以很好地提高对场星质量和年龄的估计。

附：英文原文

Title: Acoustic modes in M67 cluster stars trace deepening convective envelopes

Author: Reyes, Claudia, Stello, Dennis, Ong, Joel, Lindsay, Christopher, Hon, Marc, Bedding, Timothy R.

Issue&Volume: 2025-04-02

Abstract: Acoustic oscillations in stars are sensitive to stellar interiors1. Frequency differences between overtone modes—large separations—probe stellar density2, whereas differences between low-degree modes—small separations—probe the sound-speed gradient in the energy-generating core of main-sequence Sun-like stars3, and hence their ages. At later phases of stellar evolution, characterized by inert cores, small separations are believed to lose much of their power to probe deep interiors and become proportional to large separations4,5. Here we present evidence of a rapidly evolving convective zone as stars evolve from the subgiant phase into red giants. By measuring acoustic oscillations in 27 stars from the open cluster M67, we observe deviations of proportionality between small and large separations, which are caused by the influence of the bottom of the convective envelope. These deviations become apparent as the convective envelope penetrates deep into the star during subgiant and red giant evolutions, eventually entering an ultradeep regime that leads to the red-giant-branch luminosity bump. The tight sequence of cluster stars, free of large spreads in ages and fundamental properties, is essential for revealing the connection between the observed small separations and the chemical discontinuities occurring at the bottom of the convective envelope. We use this sequence to show that combining large and small separations can improve estimations of the masses and ages of field stars well after the main sequence.

DOI: 10.1038/s41586-025-08760-2

Source: https://www.nature.com/articles/s41586-025-08760-2