  The NASA Wide-field Infrared Survey Explorer (WISE) has discovered almost all
the known members of the new class of Y-type brown dwarfs. Most of these Y
dwarfs have been identified as isolated objects in the field. It is known that
binaries with L- and T-type brown dwarf primaries are less prevalent than
either M-dwarf or solar-type primaries, they tend to have smaller separations
and are more frequently detected in near-equal mass configurations. The binary
statistics for Y-type brown dwarfs, however, are sparse, and so it is unclear
if the same trends that hold for L- and T-type brown dwarfs also hold for
Y-type ones. In addition, the detection of binary companions to very cool Y
dwarfs may well be the best means available for discovering even colder
objects. We present results for binary properties of a sample of five WISE Y
dwarfs with the Gemini Multi-Conjugate Adaptive Optics System (GeMS). We find
no evidence for binary companions in these data, which suggests these systems
are not equal-luminosity (or equal-mass) binaries with separations larger than
~ 0.5-1.9 AU. For equal-mass binaries at an age of 5 Gyr, we find that the
binary binding energies ruled out by our observations (i.e. 10^42 erg) are
consistent with those observed in previous studies of hotter ultra-cool dwarfs.
