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 \mu m ) and W2 ( 4.6 \mu m ) 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 constinuency 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 .