Wave Transport of Angular Momentum: A New Spin on Massive-Star Evolution

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。汤森德将负责探索大质量恒星中振荡模式的波输运的发生率、特征和演化影响。这项探索的基础将在于一种新的自洽光谱（SCS）方法，该方法将传输纳入恒星演化计算。SCS方法的核心是一对数值代码：一个是非径向的，非绝热的脉动代码，将作为项目初始活动的一部分开发，一个演化代码，将从已有的代码中派生出来。当大质量恒星在主序星系中演化时，它们会经过一个或多个不稳定带，在这些不稳定带的振荡模式是由一个调节不透明度的热机激发的。在这些阶段，不稳定模式可以通过将角动量从内部的一部分传递到另一部分来改变恒星的旋转轮廓。这种波传输对恒星的后续演化和最终命运有着潜在的深远影响，但在目前的研究中，它在很大程度上被忽视了。SCS方法将首先用于探索在早期试点研究中发现的各种波输运现象：通过角速度梯度建立的模态振幅的自我限制；逆行重力模式对表层的加速度及其与Be-star现象的关系；以及由于波传递和剪切不稳定性的相互作用而产生的分子量梯度区的混合。随后，该方法将应用于全面研究包含波输运的大质量恒星演化。这一调查基于对进化轨迹的大型网格的计算，将用于解决与波输运有关的许多重要问题，从它的观测诊断到它对最终进化结果的影响。项目结果将以期刊论文、演示、计算数据、参数模型和基于浏览器的恒星演化代码的形式传播，用于研究和教育。脉动代码将在开源许可下发布，以鼓励其他团体参与探索波传输，同时也作为大质量恒星的星震学分析工具。组成项目团队的研究生和博士后研究员将受益于在科学可见度和相关性稳步增长的主题上的培训。这种培训反过来又会刺激本科/研究生课程新教材的开发。项目成果将通过论文、报告、数据和模型广泛传播。此外，随着源代码的发布和在线工具的开发，该项目将加强研究和教育的基础设施。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Dr. Townsend will undertake an exploration of the incidence, characteristics and evolutionary impact of wave transport by oscillation modes in massive stars. The foundation for this exploration will lie in a new Self-Consistent Spectrum (SCS) method for incorporating the transport into stellar evolution calculations. At the heart of the SCS method is a pair of numerical codes: a non-radial, non-adiabatic pulsation code, which will be developed as part of the project's initial activities, and an evolution code, which will be derived from an already-existing code. As massive stars evolve across the main sequence, they pass through one or more instability strips where oscillation modes are excited by an opacity-regulated heat engine. During these phases, the unstable modes can alter a star's rotation profile by transporting angular momentum from one part of the interior to another. This wave transport has potentially far-reaching consequences for the star's subsequent evolution and ultimate fate, but in studies so far it has largely been overlooked. The SCS method will first be used to explore various wave-transport phenomena discovered during an earlier pilot study: the self-limitation of mode amplitudes via the angular velocity gradients that they establish; the acceleration of surface layers by retrograde gravity modes, and its relation to the Be-star phenomenon; and the mixing of molecular weight gradient zones due to the interplay between wave transport and shear instability. Subsequently, the method will be applied in a comprehensive survey of massive-star evolution with the full inclusion of wave transport. This survey, based around the calculation of a large grid of evolutionary tracks, will be used to address many important questions relating to the wave transport, ranging from its observational diagnostics through to its impact on final evolutionary outcomes. The project results will be disseminated in the form of journal papers, presentations, calculation data, parametric models, and a browser-based stellar evolution code for research and education. The pulsation code will be released under an open-source license, to encourage other groups' involvement in exploring wave transport, and also as an analysis tool for asteroseismology of massive stars. A graduate student and postdoctoral researcher composing part of the project team will benefit from training in topics with steadily growing scientific visibility and relevance. This training will in turn stimulate the development of new curriculum materials for undergraduate/graduate courses. The project results will be broadly disseminated through papers, presentations, data and models. Moreover, with the release of source code and the development of on-line tools, the project will enhance infrastructure for research and education.