Spitzer Space Telescope - General Observer Proposal #30432


Are metal-rich hot white dwarfs accreting from dust disks or
substellar companions?

Principal Investigator: Matt Burleigh
           Institution: University of Leicester

Co-Investigators: 
Martin Barstow, University of Leicester (UK)                          
Paul Dobbie, University of Leicester (UK)                             
Ralf Napiwotzki, University of Hertfordshire (UK)                     
Carolyn Brinkworth, Spitzer Science Center / JPL                      
Donald Hoard, Spitzer Science Center                                  
Stefanie Wachter, Spitzer Science Center                              
Hans Zinnecker, Astrophysikalisches Institut Potsdam (Germany)        
Susanne Freidrich, MPE (Germany)                                      
Serge Correia, Astrophysikalisches Institut Potsdam (Germany)         

Science Category: evolved stars/pn/sne 
 Observing Modes: IracMap 
  Hours Approved: 13.9 

Abstract:
Previous mid-IR observations of white dwarf stars have revealed that a
small number possess debris dust disks and brown dwarf companions,
marked by a mid-IR photometric excess over the expected flux from the
white dwarf photosphere.  The debris dust disks may originate from the
tidal disruption of an asteroid or comet, indicating the presence of
an old solar system.  These disks have specifically been seen in a
subset of cool white dwarfs with metal-rich atmospheres (the DAZs) and
with temperatures between 10,000K and 15,000K.  The white dwarfs are
thought to accrete from this dusty material.  We propose to survey
with Spitzer a sample of much hotter white dwarfs (T>30,000K) which
also have peculiar, unexplained metal abundances (determined by us
from previous soft x-ray, EUV and far-UV observations).  Through
searching for excess mid-IR emission with IRAC, we aim to determine
whether these white dwarfs also possess debris dust disks, from which
they are accreting.  Alternatively, these mid-IR observations may
reveal the presence of close, substellar companions that are
influencing the white dwarfs' atmospheric composition via wind
accretion.