Spitzer Space Telescope - General Observer Proposal #50118


Planetary debris disks around hot white dwarfs - dusty extensions to hot gaseous
disks

Principal Investigator: Carolyn Brinkworth
           Institution: Caltech/JPL

     Technical Contact: Carolyn Brinkworth, Caltech/JPL

Co-Investigators: 
Boris Gaensicke, University of Warwick                                
Tom Marsh, University of Warwick, UK                                  
Donald Hoard, Spitzer Science Center                                  

Science Category: circumstellar/debris disks 
 Observing Modes: IracMap MipsPhot IrsPeakupImage 
  Hours Approved: 5 

Abstract:
While >250 extrasolar planets orbiting main sequence stars have been discovered,
the destiny of planetary systems through the late stages of evolution of their
host stars is very uncertain, and no planet has ever been found around a white
dwarf. We identified metal-rich gas disks around two relatively young white
dwarfs, SDSS 1228+1040 and SDSS 1043+0855. The likely origin of such a disk is a
tidally disrupted asteroid, which has been destabilised from its initial orbit
of more than 1000 solar radii by interaction with a relatively massive
planetessimal or planet. Our Spitzer Cycle 4 photometry of SDSS 1228+1040
detected a cool, dusty extension to the warm gaseous disk. Preliminary modelling
of the infrared excess suggests that it cannot be modelled with a single
optically-thick or -thin dusty debris disk, but instead requires a two-stage
disk, with an optically thick inner disk, and an optically thin cooler outer
disk. Intriguingly, the SED increased faster towards 16 microns than we
expected, and our modelling suggests that the disk cannot be continuous, but
must have a gap of about 100 Earth-radii between the optically thick and
optically thin disks. The most likely mechanism for clearing a gap in a dust
disk is the presence of a planetessimal still intact around the star. Here we
propose to observe this disk at longer wavelengths to further constrain our
model and confirm the presence of this gap in the disk, and to carry out a
similar study on a third, almost identical hot, single WD recently identified in
the Sloan Digital Sky Survey.