  Over a quarter of white dwarfs have photospheric metal pollution, which is
evidence for recent accretion of exoplanetary material. While a wide range of
mechanisms have been proposed to account for this pollution, there are
currently few observational constraints to differentiate between them. To
investigate the driving mechanism, we observe a sample of polluted and
non-polluted white dwarfs in wide binary systems with main-sequence stars.
Using the companion stars' metallicities as a proxy for the white dwarfs'
primordial metallicities, we compare the metallicities of polluted and
non-polluted systems. Because there is a well-known correlation between giant
planet occurrence and higher metallicity (with a stronger correlation for
close-in and eccentric planets), these metallicity distributions can be used to
probe the role of gas giants in white dwarf accretion. We find that the
metallicity distributions of polluted and non-polluted systems are consistent
with the hypothesis that both samples have the same underlying metallicity
distribution. However, we note that this result is likely biased by several
selection effects. Additionally, we find no significant trend between white
dwarf accretion rates and metallicity. These findings suggest that giant
planets are not the dominant cause of white dwarf accretion events in binary
systems.
