利用p-g混合模式研究亚巨星和红巨星的结构与演化

Subgiants and red giants (i.e., gaints) are evolved stars which have a hydrogen-depleted core surrounded by a hydrogen-burning shell. It is important to probe the inner structure and evolution of these evolved stars, which is also helpful in studying other questions, such as the nuclear processes in extremely dense material, and transport of angular momentum through differential rotation. As an elegant tool to study the internal structure of stars, asteroseismology has been developed rapidly in recent decades. For solar-like stars, there are two main pulsation modes confined inside them: pressure (p) modes and gravity (g) modes. For the p modes, pressure is the restoring force and for the g modes, buoyancy is the restoring force. When stars evolve to the giant stage, the very large gravitational acceleration in the core opens up the possibility that the p and g modes cavities could couple with each other, for which they are called mixed modes. Thanks to the high signal-to-noise photometry data from Kepler and CoRoT, the solar-like oscillations have been detected in thousands of giants. It is a robust tool to probe the internal structure and evolution of these evolved stars. So, using the p-g mixed modes frequencies and parameters, we will do the research as follows: (1) Examine the asymptotic dispersion relation for p-g mixed modes and discuss the coupling strength of p modes and g modes cavities; (2) Using the seismic parameters of the dipolar mixed modes, especially period spacing, combining with the large frequency separation, we construct the asteroseismic Hertzsprung-Russell diagram, which is an effective method to distinguish the different evolutionary stages and finely study the internal structures of giants for different masses and metallicities; (3) We add the small frequency separation and period spacing , that is sensitive to the feature in the core area, to the Yale-Birmingham Pipeline, which enables us to study the ages of individual giants and stellar clusters. It is important for study the chemical evolution of Milky Way and other galaxies, and the age-metallicity relation for the thin disc stars of the Galaxy.

亚巨星和红巨星（简称巨星）是恒星演化到后期形成的一类特殊恒星，其内部结构复杂。研究其内部结构对于认识热核反应过程及转动引起的角动量转移等问题具有重要作用。近年来，在巨星中发现的类太阳振动，尤其是p-g混合模式振动，为研究恒星内部结构和演化提供了强有力的工具；也为理论上研究重力波谐振腔（g模）和声波谐振腔(p模)之间的耦合进而探测恒星内部结构特征提供了巨大帮助。据此，我们将利用混合模式的星震参量（1）检验巨星阶段星震标度关系，讨论p、g模式谐振腔间的耦合问题；（2）利用偶极混合模式星震参量，尤其是周期间隔，构造新的星震赫罗图，探测和区分不同质量不同金属丰度恒星的演化状态和内部精细结构；（3）完善Yale-Birmingham pipeline并对巨星及星团的年龄进行精确求解。从而对研究银河系及其他星系化学元素丰度的演化、银盘恒星的年龄-金属丰度关系等问题提供帮助。

亚巨星和红巨星 (简称巨星)是恒星演化到后期形成的一类特殊恒星，其内部结构复杂。由于巨星的亮度较高，所以空间卫星观测到的大部分目标星为巨星。在巨星中发现的类太阳振动，尤其是p-g混合模式振动，为研究恒星内部结构、演化、恒星参量（质量、年龄、元素丰度等）提供了强有力的工具。据此在本项目中，我们利用了巨星振动的p-g混合模式的星震频率和参量进行了一系列的研究：(1)利用星震参量（周期间隔和大频率间隔）构建了不同质量和金属丰度的亚巨星和红巨星的星震赫罗图。由于周期间隔随年龄单调递减，大频率间隔与质量密切相关，所以在星震赫罗图上计算了等时线，从而可以快速获取大样本恒星的演化年龄和质量。 (2) 对双星系统HD176465恒星表面的氦元素丰度进行了研究求解。由于低质量恒星光球层温度较低(低于12000K) 无法激发氦线，所以很难通过传统光谱观测直接获取氦丰度。我们直接利用观测的振动频率，对频率中突变信号进行非线性拟合，直接精确求解得到低温小质量恒星表面的氦元素丰度。（3）对疏散星团NGC6866视场中5颗类太阳振动红巨星的年龄和星团成员性进行了星震学研究。利用Yale-Birmingham Pipeline结合星震学方法分析并推导了5颗红巨星的年龄、质量、半径、重力加速度等参量。同时将Kepler观测与LAMOST望远镜观测数据做交叉证认，确定出了星团成员星。同时，恒星的星震学年龄也可以作为星团年龄的进一步验证和限制。（4）利用观测的p-g混合振动模式频率，对KIC 8263801的演化状态（是红巨星还是红团簇巨星）进行了星震学分析。与纯声速模式不同，通过混合模式振动可以探测恒星的内核，从而获得恒星内部的结构特征和演化信息。通过对构建的最优模型的内部结构进行分析，发现恒星内核并没有氦燃烧，由此推断出KIC 8263801是处在红巨星分支阶段，而不是红团簇演化阶段。