Stability and Evolution of Interacting Close Binary Stars

Ast 0406726 Pi Webbink与单星演化不同，单星演化在第一近似值上只是初始质量和化学组成的函数，相互作用的双星的演化至少涉及四个参数：两颗恒星的质量、它们的轨道分离(或周期)和化学组成。大量的参数使得探索每一种可能的组合的成本都高得令人望而却步。此外，理论还不能严格量化许多关键的物理过程，尤其是双星在组件之间进行质量交换所造成的质量和角动量损失的程度。统计模型试图再现不同类型的紧密双星系统的可观测特性的分布(人口合成模型)，为洞察这些影响的大小提供了机会。这些模型依赖于单星演化模型的简单参数化，结合了对相互作用的双星如何基于已发表文献中相对较少数量的详细双星演化模型的行为的广泛但非常不完整的理解。这里的研究计划为种群合成模型提供了一个严格的通用框架，并探索了双星进化中研究人员广泛感兴趣的特定进化问题。这项工作包括一系列对双星进化理论的进展至关重要的项目。构建覆盖整个质量范围和演化状态的恒星的绝热和热平衡质量损失序列，将定义适用于所有类别相互作用的双星的质量转移时间尺度。用同步双星演化编码、磁场耦合双星演化和风源磁致变星模型研究了相互物理接触的双星演化。更广泛的影响：这项工作包括一名研究生，目前正在为她的博士论文做准备工作，她还将参加国内和国际会议。这项研究的三个主要组成部分涉及国际合作，研究人员在澳大利亚和德国的中国。稳定性研究的数值结果将以数字形式提供，因为它在各种双星演化研究中都有广泛的应用。最后，关于激变变星中的施主恒星变率的拟议研究为检验较低主序恒星之间的长期随机变率提供了手段。该项目还维护和开发双星数据库。

AST 0406726 PI Webbink Unlike the evolution of single stars, which is to a first approximation a function only of initial mass and chemical composition, the evolution of interacting binary stars involves at minimum four parameters: the masses of each of the two stars, their orbital separation (or period), and chemical composition. The large number of parameters makes it prohibitively expensive to explore every combination possible. Furthermore, theory is not yet able to rigorously quantify many critical physical processes, most especially the extent of mass and angular momentum loss from a binary undergoing mass exchange between components. Statistical models which attempt to reproduce the distributions of observable properties of different kinds of close binary systems (population synthesis models) offer the opportunity for insight to the magnitude of these effects. These models rely upon simple parameterizations of single-star evolution models, combined with a broad, but very incomplete, understanding of how interacting binary stars evolve based on the behavior of the relatively small number of detailed binary evolutionary models in the published literature. The research program here is providing a rigorous general framework for population synthesis models, as well as exploring specific evolutionary problems of widespread interest to researchers in binary star evolution. The work encompasses an array of projects critical to progress in binary evolution theory. Construction of adiabatic and thermal-equilibrium mass loss sequences for stars spanning the entire range of the masses and evolutionary states will define mass transfer time scales appropriate to all classes of interacting binary stars. The evolution of binary stars in physical contact with each other is explored with a simultaneous binary evolution code, magnetic field coupling to binary evolution among the magnetic cataclysmic binaries, and the modeling of wind-fed magnetic cataclysmic variables. Broader Impacts: This work includes a graduate student, now engaged in preparatory work for her Ph.D. dissertation, who will also participate in national and international conferences. Three of the major components of this research involve international collaborations, with researchers in China, Australia, and Germany. The numerical results of the stability study are to be made available in digital form, since it has broad application for all kinds of binary evolution studies. And finally, the proposed studies of donor star variability in cataclysmic variables provide the means to test for long-term stochastic variability among lower-main-sequence stars. This project also maintains and develops binary star databases.