We report new nearby L and late-M dwarfs ( d _ { phot } ~ { } \leq~ { } 30 pc ) discovered in our search for nearby ultracool dwarfs ( I - J \geq 3.0 , later than M8.0 ) at low Galactic latitude ( |b| < 15 \degr ) over 4,800 square degrees in the DENIS database .
We used late-M ( \geq M8.0 ) , L , and T dwarfs with accurate trigonometric parallaxes to calibrate the M _ { J } versus I - J colour-luminosity relation .
The resulting photometric distances have standard errors of \sim 15 \% , which we used to select candidates d _ { phot } ~ { } \leq~ { } 30 pc .
We measured proper motions from multi-epoch images found in the public archives ALADIN , DSS , 2MASS , DENIS , with at least three distinct epochs and time baselines of 10 to 21 years .
We then used a Maximum Reduced Proper Motion cutoff to select 28 candidates as ultracool dwarfs ( M8.0–L8.0 ) and to reject one as a distant red star .
No T dwarf candidates were found in this search which required an object to be detected in all three DENIS bands .
Our low-resolution optical spectra confirmed that 26 of them were indeed ultracool dwarfs , with spectral types from M8.0 to L5.5 .
Two contaminants and one rejected by the Maximum Reduced Proper Motion cutoff were all reddened F-K main sequence stars .
20 of these 26 ultracool dwarfs are new nearby ultracool dwarf members , three L dwarfs within 15 pc with one L3.5 at only \sim 10 pc .
We determine a stellar density of \overline { \Phi } _ { J~ { } cor } = ( 1.64 \pm 0.46 ) .10 ^ { -3 } dwarfs pc ^ { -3 } mag ^ { -1 } over 11.1 \leq M _ { J } \leq 13.1 based on that sample of M8–L3.5 ultracool dwarfs .
Our ultracool dwarf density value is in good agreement with the Cruz et al .
measurement of the ultracool dwarf density at high Galactic latitude .