Steinn Sigurdsson: Planets round WDs

UMCP colloquium by Steinn Sigurdsson on finding planets around WDs. The idea is to look at a system where the contrast between star and planet is less. DAX WDs are H WDs but with metal lines in their atmospheres. The lifetimes for such lines are short since they should settle. One theory is that the WDs are being bombarded by comets (note that Lee Mundy wondered about X-ray flares in this case). However comet rates are ~100 times too low. Steinn worked out that if there is a planetary system then comet rates could be increased as required. So searched 6 nearby DAZs with HST. Found a number of candidates none of which have been confirmed by proper motion tests. Impressive image taken with Gemini(N) AO system where they guided on the WD to get a 50 mas resolution.