Abstract:
Debris disks are dust disks produced by pulverizing sub-planetary objects, such as asteroids, KBOs, and comets. Debris disks can be detected through IR excess, and because of their larger surface areas they are easier than planets to detect. For stars similar to the Sun, spectral types of F to K, Spitzer MIPS 24 and 70 micron observations can probe debris disks at locations of Asteroid Belt and Kuiper Belt, respectively. As a star evolve to its final state of white dwarf (WD), a significant fraction of the stellar mass has been ejected to form a planetary nebula, which is not gravitationally bound to the star and its planetary system. It is conceivable that a planetary system would dynamically evolve along the late stellar evolution. Debris disks have been detected around cool WDs (~10,000 K) at distances <<0.01 AU; their locations within the Roche limit and the enhanced metal abundances in the WD atmospheres both point to an origin of tidally disrupted asteroids. A different type of debris disk is recently detected around the central hot WD (110,000 K) of the Helix Nebula. Spitzer MIPS observations revealed bright emission from this hot WD at 24 and 70 microns. This IR excess has been suggested to originate from a debris disk produced by collisions among KBOs. If true, the high temperatures of hot WDs, >100,000 K, provide a unique opportunity to take a last glimpse at the outer planetary system of a star. We have made a Spitzer MIPS 24 micron survey of 73 hot WDs and made follow-up IRS observations to probe the nature of the detected IR excesses. The results will be discussed.
Coffee and tea will be served 20 minutes prior to the seminar.