演化晚期恒星振动模式调制性质研究

White dwarfs and hot B subdwarfs are at the evloved phase of low mass stars. When they evolve across the instability stripes, their luminosity reveals variations as they begin to oscillate. Amplitude and frequency modulations of oscillation modes in those types of pulsating stars is well predicted by nonlinear stellar oscillation theory. Due to nonlinear weak interactions between involved modes, the discovery of these phenomena is particular difficult. Thanks for the successful launch of Kepler, now it is possible to have systematic investigation on this field. Our project is exactly on that path based on the ultra-high precise photometry collected by Kepler and TESS mission. Due to the faintness of those stars, only about twenty targets will be suitable for our projects where they are in the Kepler original field and TESS continous viewing zone. We will characterize the precise patterns of amplitude and frequency modulations of resonant modes aiming at investigate their stability and variability over a large number of modes. With the precise resolved eigen frequencies, the precise seismic models will be performed on the most interesting targets. Our works will, observationally, give solid contraints on the nonlinear coefficients within the amplitude equation formalism, as well as the linear growth rates of the resonant modes. The successful results will basically change our view on the knowledge of variability and stability of oscillation modes in compact pulsators, paving an avenue to move the nonlinear theory of stellar oscillation further.

白矮星和B型热亚矮星是中小质量恒星演化晚期形态，其穿越不稳定带时会发生振动。而振动模式的频率和振幅调制是恒星非线性振动理论的一个重要预言。由于该现象的观测研究对数据质量要求极高，直到近年来Kepler卫星提供了超高精度观测数据，才使得该领域研究成为可能。本项目将基于Kepler和TESS卫星的超高精度测光数据，系统地开展脉动白矮星和B型热亚矮星振动模式调制性质及其规律的研究。利用空间观测一年以上的连续数据，可分析这两类演化晚期恒星振动模式的振幅和频率在时域上的调制性质，确定调制形式，构建精确星震学模型，从而在观测上限制非线性振动的关键物理量，得出振动模式的线性增长率。预期研究结果将增进对恒星振动模式调制的认识，推动恒星振动理论的进一步发展。

演化晚期恒星呈现出丰富的振动模式，是线性到非线性星震学研究的重要对象。空间卫星获取的高精度测光数据为该方向研究带来了重要契机。基于Kepler和TESS测光数据，本项目开展了演化晚期恒星的振动模式调制性质研究，旨在为非线性星震学理论发展提供关键物理量的观测限制。在项目执行期间，共计发表论文13篇，包括SCI文章12篇，其中第一作者论文3篇（SCI论文2篇），通讯作者4篇。取得的主要创新成果有：1）系统地研究了Kepler天区演化晚期恒星的振动模式调制性质，发现了振幅调制的不唯一性，确定了频率调制对非线性振幅方程理论发展的重要性；2）提出了应用图像直接对照方法确定振幅调制的本征性，首次确定了振动模式振幅和频率调制的短时标性质，为非线性星震学研究提供了新思路；3）新发现了一颗氦大气脉动白矮星（DBV）并构建了精确星震学模型，确定其为迄今最冷的DBV，超出了DBV理论不稳定范围，为发展表层对流与振动相互作用提供了观测限制；4）发展了振动模式调制的物理应用，例如辅助证认超奈奎斯特频率；5）参与了国际上TESS卫星首光数据在演化晚期恒星的研究。此外，6）发布了一批LAMOST高质量同质均源的参数星表和数据库，基于这些光谱并结合空间卫星测光数据，在脉动变星、双星物理和行星科学方面取得了一定进展。