  We have searched the WISE first data release for widely separated (<10,000AU)
late T dwarf companions to Hipparcos and Gliese stars. We have discovered a new
binary system containing a K-band suppressed T8p dwarf WISEP J1423+0116 and the
mildly metal poor ([Fe/H]=-0.38+-0.06) primary BD+01 2920 (Hip 70319), a G1
dwarf at a distance of 17.2pc. This new benchmark has Teff=680+-55K and a mass
of 20-50 Mjup. Its spectral properties are well modelled except for known
discrepancies in the Y and K bands. Based on the well determined metallicity of
its companion, the properties of BD+01 2920B imply that the currently known T
dwarfs are dominated by young low-mass objects. We also present an accurate
proper motion for the T8.5 dwarf WISEP J075003.84+272544.8.
