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

该项目是Frank博士和Blackman博士努力更好地了解行星状星云形成过程以及低质量和中等质量恒星演化后期阶段的延续。作为这类恒星质量损失的最后阶段，行星状星云代表了质量和化学演化周期中的关键步骤，超过一半的物质喷射到星际介质中。行星状星云的普遍存在和易于观察也使它们成为测试新天体物理理论的首要实验室。 最近，行星状星云及其前身（前行星状星云）的高分辨率图像引发了对星云成形和恒星演化的主导模型的重新评估。对行星前星云的研究表明，它们是准直的，并驱动着缺乏足够亮度的辐射驱动的高能外流。因此，行星状星云以及行星状星云的发射或准直不能被认为是可以理解的。 根据新的数据，前行星状星云和行星状星云演化的理论，以及暗示的恒星演化后期工作过程的想法正在进行根本性的修正。一个新的图像正在出现，其中双星和磁流体动力学（MHD）过程是大多数行星状星云和行星状星云的原因。Frank博士和Blackman博士先前的工作已经确定了磁离心发射过程在这些系统中的潜在功效。他们已经展示了双星伴星为磁流体动力学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限制。该项目将以这一进展为基础，实现三个具体目标：1）提供一个更准确的说明，由发电机提供的领域条件在二进制，2）探索形成的磁盘，流出所产生的磁盘，以及产生的形态和观测特征; 3）理解由二元驱动发电机产生的磁塔爆炸。目标2和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，该项目将为伦敦帝国学院的一系列实验室天体物理学实验提供持续的理论支持，这些实验对天体物理学具有广泛的意义，并与行星前星云和行星状星云直接相关。在天体物理学中，来自中心引力源的准直外流是一种普遍存在的现象。 在新形成的恒星、高度演化的高质量恒星、双星中的致密天体、星暴星系和为活动星系核提供动力的超大质量黑洞中，都可以观察到喷流和更宽的双极外流。 在超新星和伽马射线爆发的模型中也会用到准直外流。 虽然这项工作的重点是行星状星云，它将直接相关的理论和观测的意义上，让行星状星云作为一个试验台的理论MHD流出这些其他领域。 与帝国学院集团的合作将有助于深化快速发展的高能密度实验室天体物理学领域。 开发AstroBEAR代码的工作对于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特别有益。 最后，该计划还包括一个创新的推广计划，涉及科学互动的创建：基于模拟的学习模块，将张贴在全国最受欢迎的科学杂志网站。

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.