  We identify 806 ultra-cool dwarfs from their SDSS riz photometry (of which 34
are newly discovered L dwarfs) and obtain proper motions through cross matching
with UKIDSS and 2MASS. Proper motion and distance constraints show that nine of
our ultra-cool dwarfs are members of widely separated binary systems; SDSS 0101
(K5V+M9.5V), SDSS 0207 (M1.5V+L3V), SDSS 0832 (K3III+L3.5V), SDSS 0858
(M4V+L0V), SDSS 0953 (M4V+M9.5V), SDSS 0956 (M2V+M9V), SDSS 1304 (M4.5V+L0V),
SDSS 1631 (M5.5V+M8V), SDSS 1638 (M4V+L0V). One of these (SDSS 0832) is shown
to be a companion to the bright K3 giant Eta Cancri. Such primaries can provide
age and metallicity constraints for any companion objects, yielding excellent
benchmark objects. Eta Cancri AB is the first wide ultra-cool dwarf + giant
binary system identified. We present new observations and analysis that
constrain the metallicity of Eta Cancri A to be near solar, and use recent
evolutionary models to constrain the age of the giant to be 2.2-6.1 Gyr. If Eta
Cancri B is a single object, we estimate its physical attributes to be; mass =
63-82 M_Jup, T_eff = 1800+/-150 K, log g = 5.3-5.5, [M/H] = 0.0+/-0.1. Its
colours are non typical when compared to other ultra-cool dwarfs, and we also
assess the possibility that Eta Cancri B is itself an unresolved binary,
showing that the combined light of an L4 + T4 system could provide a reasonable
explanation for its colours.
