Program: GN-2009B-Q-74

~~~~White dwarfs (WDs) allow us to take a last glimpse of extrasolar planetary systems at their final evolutionary stage. No planets around WDs have been detected directly, however, two types of debris disks associated with subplanetary objects have been detected: (1) small dust disks around cool WDs replenished by tidally disrupted asteroids, and (2) large dust disks around hot WDs generated by collisions among Kuiper-Belt-like objects (KBOs). \vspace{-0.15 cm} ~~~~To search for the latter dust disks, we made a Spitzer MIPS 24 $\mu$m survey of 72 hot WDs and found IR excesses for 7, all of which are central stars of planetary nebulae (CSPNs). We have also searched Spitzer's archive and identified 5 additional CSPNs with near- to mid-IR excesses. The spectral energy distribution of some IR excesses resemble those of post-AGB binaries, raising the suspicion that some of the IR excesses we have detected may originate from binary interactions. \vspace{-0.15 cm} ~~~~~We request Gemini Michelle 8-14 $\mu$m spectroscopic observations of CSPN NGC 6804, a bright CSPN with IR excess between 1-24 $\mu$m, in order to separate the dust continuum from nebular line emission and model the spectra to estimate the distribution and temperature of the dust disk. Any detected PAH and mineralogical features will help assess the grain size and composition. These physical properties will allow us to determine the origin and nature of the dust disk of NGC 6804.