Program: GS-2008B-Q-10

Many post-AGB systems show peculiar abundance patterns which can be explained by processing of material on circumstellar grains. The SEDs frequently reveal a NIR excess due to dust at temperatures close to sublimation. Well studied systems are known to be single lined spectroscopic binaries. These systems have gone through a period of common envelope evolution which has formed a circumstellar disk. De Ruyter et al. (2006) lists 51 objects of this type. The dust disks are being imaged by various groups. We propose a first survey of gas in post-AGB disks. The spectra will yield the velocity of the gas at the inner disk edge and permit a search for isotopic variants. Keplerian motion will give the masses of the inner binary system. There is a striking similarity between the disks around binary post-AGB and Herbig Ae/Be group II sources. Combining gas phase information and high spatial resolution data, it will be possible to define and extend the analogies between the intensively studied YSO disks and the material around post-AGB stars which are only now being studied as a class.