The Distribution of Debris Disks around Solar-Type Stars
          Geoffrey Bryden, JPL
          Chas Beichman, MSC
          David Trilling, Arizona
          George Rieke, Arizona
          Karl Stapelfeldt, JPL
          Mike Werner, JPL

          Using the MIPS camera on the Spitzer Space Telescope, we have searched for infrared excesses around 58 FGK main-sequence field stars.  With a median age of ~5 Gyr, the stars are older than those which typically have excess emission due to a debris disk. Nevertheless, we have detected 70 micron excesses around 6 stars at the 3-sigma confidence level.  This extra emission is produced by cool material (<100 K) located beyond 10 AU, well outside the ''habitable zones'' of these systems and consistent with the presence of Kuiper Belt analogues with ~100 times more emitting surface area than in our own planetary system.  Only one star, HD69830, shows excess emission at 24 microns, corresponding to dust with temperatures > 300 K located inside of 1 AU.  While debris disks with L_disk/L_* > 10^-3 are rare around old FGK stars, we find that the disk frequency increases from 2+-2% for disks with L_disk/L_* > 10^-4 to 11+-5% for L_d/L_* > 10^-5.  Fits of this distribution suggest that the amount of dust in our Solar System is not largely below the average for similar field stars.