From Core to Outflow: Binaries, MHD and the Origin of Planetary/ Pre-Planetary Nebulae

该项目是弗兰克博士和布莱克曼博士为更好地理解行星状星云的形成过程以及中低质量恒星演化的后期阶段而做出的努力的延续。作为这类恒星质量损失的最后阶段，行星状星云代表着喷出到星际介质中的一半以上物质的质量和化学演化周期中的关键一步。行星状星云的普遍存在及其观测的简便性也使它们成为测试新天体物理理论的首选实验室。最近，行星星云及其前身(行星前星云)的高分辨率图像引发了对星云形成和恒星演化的主导模型的关键重新评估。对行星前星云的研究表明，它们是准直的，并驱动能量外流，而这些外流缺乏足够的光度来进行辐射驱动。因此，行星前星云的发射或准直，以及行星星云的联合，都不能被认为是理解的。根据新的数据，行星前星云和行星星云演化的理论，以及恒星演化后期工作过程的想法，正在经历根本性的修改。一幅新的图景正在浮现，其中双星和磁流体(MHD)过程是行星前星云和行星星云的主要原因。弗兰克博士和布莱克曼博士之前的工作已经确定了磁力离心式发射过程在这些系统中的潜在功效。他们展示了双星伴星为MHD发射创造条件的途径，包括双星发电机过程的有效性及其在单星中的极限。该项目将以这一进展为基础，以三个具体目标为基础：1)提供双星发电机提供的场条件的更准确的描述；2)探索盘的形成、由这种盘产生的流出以及产生的形态和观测特征；3)了解双星驱动的发电机产生磁塔爆炸的原因。目标2和目标3将使用由Frank博士和合作者开发的新的自适应网格细化MHD代码(AstroBEAR)来实现。此外，该项目将继续为伦敦帝国理工学院的一系列实验室天体物理实验提供理论支持，这些实验对天体物理学具有广泛的兴趣，并与行星前星云和行星状星云直接相关。中心引力源的准直流出是天体物理学中普遍存在的现象。在新形成的恒星、高度演化的大质量恒星、双星中的致密物体、星暴星系和为活跃星系核提供动力的超大质量黑洞中，可以观察到喷流和更广泛的双极外流。在超新星和伽马射线爆发的模型中也引用了准直外流。虽然这项工作主要集中在行星星云上，但从允许行星星云作为MHD外流理论的试验台的意义上来说，它将与这些其他领域在理论和观测上都有直接的关联。与帝国理工学院集团的合作将有助于深化快速增长的高能密度实验室天体物理学领域。开发AstroBEAR代码的工作在继续研究新的多物理方法以及培训下一代计算天体物理学家方面特别有益。最后，该计划还包括一个创新的推广计划，涉及创建科学互动：基于模拟的学习模块，该模块将发布在美国最受欢迎的科学杂志网站上。

This project is a continuation of Dr. Frank and Dr. Blackman's efforts better to understand the process of planetary nebula formation and the late stages of evolution of low and intermediate mass stars. As the final stage of mass loss for such stars, planetary nebulae represent a critical step in the mass and chemical evolution cycle for more than half the material ejected into the interstellar medium. The ubiquity of planetary nebulae and their ease of observation have also made them premier laboratories for testing new astrophysical theories. Recently, high-resolution images of planetary nebulae and their progenitors (pre-planetary nebulae) have triggered a critical re-evaluation of the dominant model for both nebular shaping and stellar evolution. Studies of pre-planetary nebulae show them to be collimated and to drive energetic outflows that lack sufficient luminosity for radiative driving. The launching or collimation of pre-planetary nebulae, and by association planetary nebulae, therefore cannot be considered to be understood. In light of new data the theory of pre-planetary and planetary nebulae evolution and, by implication, ideas about processes at work in the late stages of stellar evolution are undergoing fundamental revision. A new picture is emerging in which binaries and magnetohydrodynamic (MHD) processes are responsible for the majority of pre-planetary and planetary nebulae. Previous work by Drs. Frank and Blackman has established the potential efficacy of magneto-centrifugal launching processes in these systems. They have shown the pathways by which binary companions can create conditions for MHD launching, including the efficacy of dynamo processes in binary stars and its limits in single stars.This project will build on this progress with three specific goals: 1) to provide a more accurate account of the field conditions supplied by dynamos in binaries, 2) to explore the formation of disks, the outflows generated by such disks, and the morphology and observational signatures produced, and 3) to understand the generation of magnetic tower explosions by binary driven dynamos. Goals 2 and 3 will be achieved using a new adaptive mesh refinement MHD code (AstroBEAR) developed by Dr. Frank and collaborators. Additionally, the project will provide continued theoretical support for a series of laboratory astrophysics experiments at Imperial College in London, which are of broad interest to astrophysics and directly relevant to pre-planetary and planetary nebulae. Collimated outflows from a central gravitating source are a ubiquitous phenomenon in astrophysics. Jets and wider bipolar outflows are observed in newly forming stars, highly evolved high mass stars, compact objects in binaries, starburst galaxies, and supermassive black holes powering active galactic nuclei. Collimated outflows are also invoked in models for supernovae and gamma ray bursts. While this work is focused on planetary nebulae it will be of direct relevance to these other fields both theoretically and observationally in the sense of allowing planetary nebula to act as a test-bed for theories of MHD outflows. The collaboration with the Imperial Collage group will help to deepen the rapidly growing field of High Energy Density Laboratory Astrophysics. The work developing the AstroBEAR code is of particular benefit in continuing research with new multi-physics methods as well as training the next generation of computational astrophysicists. Finally this program also includes an innovative outreach program involving the creation of Sci-Interactives: simulation based learning modules which will be posted on the nation's most popular science magazine websites.