Program: GN-2009A-C-7

Dust disks have been detected around white dwarfs (WDs), and they appear to bifurcate into (1) small dust disks around cool WDs that are replenished by tidally disrupted asteroids, and (2) large dust disks around hot WDs that have been suggested to be generated by collisions among Kuiper-Belt-like objects. We have made a Spitzer MIPS 24 $\mu$m survey of 72 hot WDs and found IR excess for 7, all of which are central stars of planetary nebulae (CSPNs). Inspired by these results, we have further examined archival Spitzer IRAC and MIPS observations of 56 planetary nebulae (PNe) and identified 5 CSPNs with near- to mid-IR excesses. Thus far, dust disks have been detected around binary post-AGB stars, CSPNs, and WDs, but it is not clear if some dust disks have a common origin and persist through the stellar evolution. It is necessary to establish physical parameters of the dust disks around CSPNs for comparison with the others. We therefore request Gemini NIRI and Michelle observations of five CSPNs with IR excesses. We will search for PAH and mineralogical features in order to assess the grain size and composition, and model the spectra to estimate the distribution and temperature of the dust disks. These physical properties will allow us to determine the origin and nature of the dust disks, and help us understand the evolution of planetary systems and the relationship between PNe and binary CSPNs.