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.

Project Report

Collimated mass outflows are ubiquitous phenomena in astrophysics. Jets and bipolar outflows are observed in systems as diverse as newly forming low mass stars, young and evolved high mass stars , micro-quasars, starburst galaxies, and AGN . Collimated outflows are also at the heart of newer models for both supernovae and gamma ray bursts . The ubiquity of these jets/outflows suggests a common mechanism for their formation. A combination of central source rotation, dynamically significant magnetic fields and accretion flows have provided key links in the development of so-called magneto-centrifugal launch models. While the success of this scenario has fueled confidence in its overall veracity, there remain many fundamental questions to be answered including basic uncertainties about the links between accretion processes and outflow parameters. In this project we studied the evolution of outflows from highly evolved stars like the sun. These episodes of mass loss are a key aspect of the death of sun-like stars and the goal of our project was to understand how the outflows are generated, collimated and their effect on the pre-existing gas expelled by the star during earlier epochs. To this end we explored the generation of the outflows via magnetic fields and the creation of disks of gas around stars in binary systems such that these disks become the engines driving the outflows. A key feature of our work was the use of advanced computation methods to track the interaction of magnetic fields and gas as it is driven away from the evolved star. Part of the work involved pushing the state of the art on these tools forward such that they could run on tens of thousands of processors and thereby reach the computational speeds needed to run realistic 3-D simulations of binary stars, mass loss and magnetic fields. Our research program included a unique aspect that highlights the broad impact of our work beyond studies of PN. In our study we also included a laboratory astrophysics component in which High Energy Density Plasma Physics machines, used in Inertial Confinement Fusion studies were brought to bear on our questions. High Energy Density Laboratory Astrophysics (HEDLA) is a relatively new and growing field of transformative science that holds great promise for articulating new domains of astrophysics.

National Science Foundation (NSF)
Division of Astronomical Sciences (AST)
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Nigel Sharp
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University of Rochester
United States
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