From Central Engine to Bipolar Outflow: Binaries, MHD and the Evolution of Planetary Nebulae

弗兰克博士和他的团队研究了低质量和中等质量恒星演化的后期阶段，这些恒星演化成原行星状星云（PPN）和行星状星云（PN），并在星际介质中失去了很大一部分质量。原行星状星云经常显示出不能用辐射驱动来解释的准直的能量流出，而原行星状星云的发射或准直还不是很清楚。该团队开发了一种新的范例，其中双星和磁流体动力学过程负责大部分PPN和PN。研究人员在PPN和PN中建立了磁离心式发射过程的潜在功效，并找到了二元伴侣为磁流体动力发射创造条件的途径，包括发电机过程的功效。这里的工作集中在几个主题上：通过风捕获模拟PPN和PN双星系统中吸积盘形成的途径；在PPN/PN背景下的共同包膜演化，以了解在大量恒星包膜抛射后盘何时形成；以及磁塔射流的传播磁塔射流很可能是圆盘形成的原因。磁流体动力学流出模拟与伦敦帝国理工学院的实验室天体物理实验进行了比较，后者产生了超高速模式、辐射磁等离子体流出和射流。所有的计算使用自适应网格细化磁流体动力学，多物理场代码AstroBEAR建立在罗切斯特大学。AstroBEAR代码的并行AMR引擎将被重新设计，以使其能够达到大规模并行平台上的千兆级计算。这项工作与其他研究领域有关，在这些研究领域中，从中心重力源观察到准直流出。该项目为计算天体物理学的学生和博士后提供培训，并促进天文学家和等离子体实验家之间更紧密的联系。

Dr. Frank and his team study the late stages of stellar evolution for low and intermediate mass stars, when these stars evolve into proto planetary nebulae (PPN) and planetary nebulae (PN) and lose large fractions of their mass to the interstellar medium. Proto planetary nebulae often show collimated energetic outflows that cannot be explained by radiative driving and launching or collimation of proto planetary nebulae is not well understood. The team developed a new paradigm in which binaries and magneto-hydrodynamic processes are responsible for the majority of PPN and PN. The researchers established the potential efficacy of magneto-centrifugal launching processes in PPN and PN and found pathways by which binary companions create conditions for magneto-hydrodynamic launching including the efficacy of dynamo processes. Here the work focuses on several topics: Simulations of the pathways for accretion disk formation in PPN and PN binary systems by wind capture; common envelope evolution in the context of PPN/PN to understand when disks form after ejection of the bulk stellar envelope; and the propagation of magnetically dominated magnetic tower jets which are likely resulting in the disks. The magneto-hydrodynamic outflow simulations are compared to laboratory astrophysics experiments at Imperial College in London that generate hyper-fast mode, radiative magnetic plasma outflows and jets. All computations use the Adaptive Mesh Refinement magneto-hydrodynamic, multiphysics code AstroBEAR built at the University of Rochester. The parallel AMR engine of the AstroBEAR code will be redesigned to allow it to reach towards Petascale computing on massively parallel platforms. This work is relevant to other research areas where collimated outflows from a central gravitating source are observed. The project provides student and postdoc training in computational astrophysics and fosters closer connections between astronomers and plasma experimentalists.