Spitzer Space Telescope - General Observer Proposal #60113


A Search for Circumstellar Dust at SDSS White Dwarfs with K-Band Excess

Principal Investigator: Jay Farihi
           Institution: UCLA

     Technical Contact: Jay Farihi, UCLA

Co-Investigators: 
Boris Gaensicke, University of Warwick                                
Jonathan Girven, University of Warwick                                
Matt Burleigh, University of Leicester                                
Paul Steele, University of Leicester                                  

Science Category: extrasolar planets 
 Observing Modes: IRAC Post-Cryo Mapping
  Hours Approved: 6.7 

Abstract:
We propose IRAC 3.6 and 4.5 micron observations of white dwarfs observed to have
a K-band excess via cross-correlation of the the Sloan Digital Sky Survey (SDSS)
and the UKIRT Infrared Deep Sky Survey (UKIDSS). We have searched tens of
thousands of sources in SDSS DR7 with spectra (by eye) and/or photometry and
identified a few thousand SDSS white dwarfs with good YJHK photometry in UKIDSS.
Of those sources, we select the best seven candidates with a likely K-band
excess to search with Spitzer / IRAC for confirmation of warm circumstellar
dust. Our selection criteria should be both completely unbiased and highly
efficient relative to previous white dwarf dust disk searches. There is now
strong evidence that the closely orbiting dust disks at white dwarfs are caused
by the tidal disruption of a minor planet or planets. In addition to producing
an infrared excess, the debris also pollutes the otherwise pristine white dwarf
atmosphere with metals, via accretion. Any confirmed dust disks will almost
certainly have contaminated their white dwarf hosts, but metal absorption
features cannot typically be seen in the relatively low S/N and low resolution
SDSS spectra. However, ground- and space-based ultraviolet and optical
spectroscopy of the heavy element abundances (at high resolution and superior
S/N) will yield the bulk composition of the terrestrial, polluting material.
Our targets represent high probability of dust disk detection and, if confirmed,
will substantially increase the number of exoplanetary debris disks for which a
bulk chemical composition can be obtained.