Spitzer Space Telescope - General Observer Proposal #50340


Searching for ancient planetary systems - a Spitzer survey for planetary debris
disks around metal-rich white dwarfs

Principal Investigator: Carolyn Brinkworth
           Institution: Caltech/JPL

     Technical Contact: Carolyn Brinkworth, Caltech/JPL

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

Science Category: circumstellar/debris disks 
 Observing Modes: IracMap IrsPeakupImage 
  Hours Approved: 24 

Abstract:
Over the past decade there has been an explosion in the number of planets found
around other stars, and yet, despite this, we have very little idea of the final
fate of these planetary systems as their host stars evolve off the main sequence
and become white dwarfs. While no planet has ever been found around a white
dwarf, we have begun to piece together the puzzle of their fate with the
discovery of debris disks around a number of isolated, metal-rich white dwarfs.
White dwarfs are generally extremely metal-poor, since their high surface
gravity causes heavy elements to settle out of their atmospheres in a matter of
a few tens of years. Those that have metals in their atmospheres must therefore
be accreting them from some external source. Recent research has shown that the
metal abundances in these systems are too high for the system to be accreting
from the ISM, and a more likely explanation is that most or all of them are
accreting from some kind of circumstellar disk. Searches for debris disks around
these metal-rich white dwarfs have been extremely successful, with estimates
that up to 15-20% of them may have a dusty circumstellar disk. Despite this
success rate, a large number of the bright, metal-rich white dwarfs in the
McCook and Sion catalogue remain unobserved with Spitzer. We propose to observe
all of the remaining bright metal-rich white dwarfs with IRAC and, where
possible, IRS Peak-up imaging to search for debris disks in these systems.
Modelling of these disks will answer a wide range of questions about the
evolution and composition of both the disks and their planetary system
progenitors.