Luminosity function of M7-L8 ultracool dwarfs

In this paper we present optical spectroscopy of 198 candidate nearby ultracool dwarfs, including 12 late-M and L dwarfs likely to be within 20pc 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 20pc. 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_Ks_<13). We find a space density of 4.9x10^-3^/pc^3^ for late-M dwarfs (M7-M9.5) and a lower limit of 3.8x10^-3^/pc^3^ for L dwarfs.