  WISE J104915.57-531906.1 A+B and WISE J085510.83-071442.5 were recently
discovered as the third and fourth closest known systems to the Sun,
respectively (2.0 and 2.3 pc). The former consists of a L8+T0.5 binary and the
latter is a probable Y dwarf and is the coldest known brown dwarf (~250 K). We
present a search for common proper motion companions to these brown dwarfs
using multi-epoch mid-infrared images from the Spitzer Space Telescope. We have
also obtained near-infrared adaptive optics images of WISE J104915.57-531906.1
A+B with the Very Large Telescope to search for companions at smaller
separations than reached by Spitzer. No new companions are detected in either
system. At projected separations of 25-420" (50-840 AU) for WISE
J104915.57-531906.1 A+B and 4-420" (9-970 AU) for WISE J085510.83-071442.5, the
Spitzer images are sensitive to companions with M_4.5<21.6 and 21.9,
respectively, which correspond to masses of >=1 M_Jup for ages of >=1 Gyr and
temperatures of >=150 K. The detection limit in the adaptive optics images of
WISE J104915.57-531906.1 A+B is dH~10 at 3-15" (6-30 AU), or >=7 M_Jup for >=1
Gyr.
