Nearby Debris Disk Systems with High Fractional Luminosity Reconsidered

By searching the IRAS and ISO databases, we compiled a list of 60 debris disks that exhibit the highest fractional luminosity values (f_d > 10^-4) in the vicinity of the Sun (d < 120 pc). Eleven out of these 60 systems are new discoveries. Special care was taken to exclude bogus disks from the sample. We computed the fractional luminosity values using available IRAS, ISO, and Spitzer data and analyzed the Galactic space velocities of the objects. The results revealed that stars with disks of high fractional luminosity often belong to young stellar kinematic groups, providing an opportunity to obtain improved age estimates for these systems. We found that practically all disks with f_d > 5 × 10^-4 are younger than 100 Myr. The distribution of the disks in the fractional luminosity versus age diagram indicates that (1) the number of old systems with high f_d is lower than was claimed before, (2) there exist many relatively young disks of moderate fractional luminosity, and (3) comparing the observations with a current theoretical model of debris disk evolution, a general good agreement could be found.