2000AJ....119..342P

We summarize current information concerning the photometry, distances, and extinctions for the central stars of bipolar nebulae (BPNs). These are used to place tight constraints upon the properties of binary companions and to derive upper limit mass and spectral functions for these stars. A comparison of these results with model binary systems suggests that many BPN central stars may have binary companions, although these are either unrecognized or undetected. However, the photometric limits also imply that such binaries are unlikely to undergo stable mass transfer during AGB Roche lobe overflow. Constraints upon the masses of the secondary stars also enable limits to be placed upon orbital velocities, whence it is apparent that the motion of very few of these binaries is likely to be detected at current levels of observational precision.