  We present the discovery of another seven Y dwarfs from the Wide-field
Infrared Survey Explorer (WISE). Using these objects, as well as the first six
WISE Y dwarf discoveries from Cushing et al., we further explore the transition
between spectral types T and Y. We find that the T/Y boundary roughly coincides
with the spot where the J-H colors of brown dwarfs, as predicted by models,
turn back to the red. Moreover, we use preliminary trigonometric parallax
measurements to show that the T/Y boundary may also correspond to the point at
which the absolute H (1.6 um) and W2 (4.6 um) magnitudes plummet. We use these
discoveries and their preliminary distances to place them in the larger context
of the Solar Neighborhood. We present a table that updates the entire stellar
and substellar constituency within 8 parsecs of the Sun, and we show that the
current census has hydrogen-burning stars outnumbering brown dwarfs by roughly
a factor of six. This factor will decrease with time as more brown dwarfs are
identified within this volume, but unless there is a vast reservoir of cold
brown dwarfs invisible to WISE, the final space density of brown dwarfs is
still expected to fall well below that of stars. We also use these new Y dwarf
discoveries, along with newly discovered T dwarfs from WISE, to investigate the
field substellar mass function. We find that the overall space density of
late-T and early-Y dwarfs matches that from simulations describing the mass
function as a power law with slope -0.5 < alpha < 0.0; however, a power-law may
provide a poor fit to the observed object counts as a function of spectral type
because there are tantalizing hints that the number of brown dwarfs continues
to rise from late-T to early-Y. More detailed monitoring and characterization
of these Y dwarfs, along with dedicated searches aimed at identifying more
examples, are certainly required.
