I have been working with Raghvendra Sahai to try to understand the origins of plantary nebulae. The asymptotic giant branch (AGB) stars that evolve into planetary nebulae have spherical outflows, so they should form spherical nebulae. The nebulae we see, however, are often bipolar, multipolar, or irregular, suggesting we are missing a key part of the physics controlling the final evolutionary stages of sun-like stars. Some of the most promising explanations for aspherical nebulae require that the AGB star has a binary companion, but we do not have a large sample of AGB stars in binary systems with which to test such models. AGB stars with companions are difficult to identify, in part because AGB stars are 103-104 times more luminous than a hypothetical companion star would be.
Because AGB stars are relatively cool (3000 Kelvin), most of their flux is in the red or infrared. A hotter companion star can dominate the system's ultraviolet flux, producing an ultraviolet excess, despite having a much lower luminosity. We have been using guest investigator and archived photometry from the Galaxy Evolution Explorer to search for AGB stars with ultraviolet excesses. So far this program has borne fruit, and we have requested UV spectroscopy of some of our best candidates to to confirm that they are in fact binaries.
"Binarity in Cool Asymptotic Giant Branch Stars: a GALEX Search for Ultraviolet Excesses", Sahai, R.; Findeisen, K.; Gil de Paz, A.; Sanchez Contreras, C. 2008, ApJ 689 1274 ADS
"A Search for Companions to AGB Stars", Findeisen, K.; Sahai, R.; Gil de Paz, A.; Sanchez Contreras, C. 2008, in American Astronomical Society Meeting 209, #93.07 ADS