We present a 20-pc , volume-limited sample of M7–L8 dwarfs created through spectroscopic follow-up of sources selected from the Two Micron All Sky Survey ( 2MASS ) Second Incremental Release Point Source Catalog .
In this paper , we present optical spectroscopy of 198 candidate nearby ultracool dwarfs , including 12 late-M and L dwarfs likely to be within 20 pc of the Sun and 94 more distant late-type dwarfs .
We have also identified five ultracool dwarfs with spectral signatures of low-gravity .
Combining these data with previous results , we define a sample of 99 ultracool dwarfs in 91 systems within 20 pc .
These are used to estimate the J - and K -band luminosity functions for dwarfs with optical spectral types between M7 and L8 ( 10.5 < M _ { J } < 15 , 9.5 < M _ { K _ { S } } < 13 ) .
We find a space density of 4.9 \times 10 ^ { -3 } pc ^ { -3 } for late-M dwarfs ( M7–M9.5 ) and a lower limit of 3.8 \times 10 ^ { -3 } pc ^ { -3 } for L dwarfs .