Spitzer Space Telescope - General Observer Proposal #40953


MIPS Survey of Dust Disks around Hot White Dwarfs

Principal Investigator: You-Hua Chu
           Institution: University of Illinois, Urbana-Champaign

     Technical Contact: Robert Gruendl, UI, Urbana-Champaign

Co-Investigators: 
Kate Su, University of Arizona                                        
Robert Gruendl, Universtiy of Illinois, Urbana-Champaign              
Thomas Rauch, Universitat Tubingen                                    
Kevin Volk, Gemini Observatory                                        

Science Category: circumstellar/debris disks 
 Observing Modes: MipsPhot 
  Hours Approved: 15.1 

Abstract:
Spitzer observations of the Helix Nebula have revealed a bright 24 and 70 um
source at the central star, a white dwarf (WD) with an effective temperature of
110,000 K. A Spitzer IRS spectrum of this source confirms that the emission is
dust continuum. The analysis of Spitzer observations lead to the conclusion that
the hot WD is surrounded by a dust disk at a distance of 40-100 AU, and that the
dust is freshly produced by collisions of dynamically perturbed Kuiper-Belt-like
Objects (KBOs) or comets. The collisions of these KBOs/comets with the central
WD or the accretion of the dust may generate the mysterious 1 keV X-ray emission
observed from the WD. We propose a MIPS 24 um survey of a sample of hot
(>100,000 K) WDs that either are in old planetary nebulae or belong to a variety
of spectral classes to search for dust disks up to a distance of 100 AU from the
star, with a sensitivity of 34 uJy. Hot WDs provide an opportunity for the last
glimpse at the outer planetary systems of stars before they cool and fade into
oblivion. The results will be used to study the evolution of planetary systems
throughout the stellar lifetime. The proposed survey can test the hypothesis
that 1 keV X-rays can be generated by accreting comets or dust, and thus finally
solve the mystery of hard X-ray emission from single WDs.