Finding Extrasolar Planets in the Stellar Graveyard with the Hubble Space Telescope

Abstract

In order to directly image an extrasolar planet, the large contrast between a star and a companion planet must be overcome. White Dwarfs (WDs) are the remnants of stars > 1 M_sun and are orders of magnitude dimmer, making searches for planets and brown dwarfs (BDs) possible. We present the preliminary results of a survey of 7 hydrogen white dwarfs with photospheric metal lines (DAZs) for substellar and planetary objects, using NICMOS on the Hubble Space Telescope (HST). The extremely high contrast available with the NICMOS coronagraph allows 7-12 M_Jup planets to be detected to within 10-30 AU of the primary WD. This represents the first concerted search for planetary objects around stars that were more massive than the sun. Our results show that there are candidates around three of the seven stars, which are awaiting confirmation through common proper motion studies, some of which can only be confirmed through another observation with HST. Continuing studies of WDs will constrain planet formation scenarios for more massive stars and provide a sample of planets to study with future space missions such as JWST and SIM.