Jay Farihi
University of Leicester, UK
 

"Minor Planet Signatures at White Dwarfs"
 

I will present an analysis of all cool, metal-contaminated white dwarfs observed with Spitzer, including the recent discovery of two new circumstellar disks.  Extending previous studies, over 50% of all single white dwarfs with implied metal accretion rates greater than around 3e8 g/s display a warm infrared excess from orbiting dust; the likely result of a tidally-destroyed minor planet.  This benchmark accretion rate lies between the dust production rates of 1e6 g/s in the solar system zodiacal cloud and 1e10 g/s often inferred for debris disks at main sequence A-type stars.  It is estimated that between 1% and 3% of all single white dwarfs with cooling ages less than around 0.5 Gyr possess circumstellar dust, signifying an underlying population of minor planets.