The work to be carried out here centers on the common envelope phase of the evolution of close binaries, a point in the system's evolution when the companion orbits inside the envelope of the evolved primary. During this event, the spiraling in companion donates a fraction of its orbital energy to unbind and expel the envelope, resulting in a binary with a shorter period. It is the workings of this interaction, poorly understood at the moment, which dictate the properties of all evolved close binaries. Here it is postulated that the majority of, if not all, planetary nebulae central stars are post-common envelope binaries, which is contrary to the canonical view that planetary nebulae arise through the natural evolution of single stars. With this in mind, three projects will be undertaken to explore the physics of the common envelope phase, its effects of the distribution of various evolved close binary types, and the possibility that the central stars of planetary nebulae tend to indeed be binaries. First, using radial velocity techniques, initial (and suggestive) searches for binarity among central stars will be continued and extended to determine the planetary nebulae binary fraction. Second, common envelope interactions will be numerically modeled to determine the angular momentum loss as a function of primary and secondary masses as well as other stellar and system parameters. The initial hydrodynamic modeling will be undertaken with both Lagrangian Smooth Particle Hydrodynamics and an Eulerian Adaptive Mesh Refinement codes and the best suited approach will be selected to carry out the bulk of the investigation. Finally, the results of this modeling will be incorporated into a population synthesis code to test the outcome by reproducing the results of binarity among planetary nebulae established in the first project. The results of this work will be featured in outreach programs through the American Museum of Natural History, the Rose Center for Earth and Space, and the Hayden Planetarium. Visualizations of common envelope interactions will be developed for display at the Museum and included in the Science Bulletins. A course on stellar evolution with emphasis on binarity will be developed and offered on repeat occasions within the context of the Museum's evening courses. The simulation outputs and all spectroscopic data will be made available to the community through the Museum's data archives.
