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

University Of Rochester, Rochester NY

Investigators

Abstract

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.