A Word to the WISE: Confusion is Unavoidable for WISE-selected Infrared
  Excesses
  Stars with excess infrared radiation from circumstellar dust are invaluable
for studies of exoplanetary systems, informing our understanding on processes
of planet formation and destruction alike. All-sky photometric surveys have
made the identification of dusty infrared excess candidates trivial, however,
samples that rely on data from WISE are plagued with source confusion, leading
to high false positive rates. Techniques to limit its contribution to
WISE-selected samples have been developed, and their effectiveness is even more
important as we near the end-of-life of Spitzer, the only facility capable of
confirming the excess. Here, we present a Spitzer follow-up of a sample of 22
WISE-selected infrared excess candidates near the faint-end of the WISE
detection limits. Eight of the 22 excesses are deemed the result of source
confusion, with the remaining candidates all confirmed by the Spitzer data. We
consider the efficacy of ground-based near-infrared imaging and astrometric
filtering of samples to limit confusion among the sample. We find that both
techniques are worthwhile for vetting candidates, but fail to identify all of
the confused excesses, indicating that they cannot be used to confirm
WISE-selected infrared excess candidates, but only to rule them out. This
result confirms the expectation that WISE-selected infrared excess samples will
always suffer from appreciable levels of contamination, and that care should be
taken in their interpretation regardless of the filters applied.
