2007MNRAS.374..445K

We report the discovery of 21 hitherto unknown bright southern ultracool dwarfs with spectral types in the range M7 to L5.5, together with new observations of a further three late M dwarfs previously confirmed. Three more objects are already identified in the literature as high proper motion stars; we derive their spectral types for the first time. All objects were selected from the Two Micron All-Sky Survey (2MASS) all-sky and SuperCOSMOS point source data bases on the basis of their optical/near-infrared colours, J-band magnitudes and proper motions. Low-resolution (R ∼ 1000) JH spectroscopy with the European Southern Observatory (ESO)/New Technology Telescope (NTT) Son of Isaac (SOFI) spectrograph has confirmed the ultracool nature of 24 targets, out of a total of 25 candidates observed. Spectral types are derived by direct comparison with template objects and compared to results from H₂O and FeH indices. We also report the discovery of one binary, as revealed by SOFI acquisition imaging; spectra were taken for both components. The spectral types of the two components are L2 and L4 and the distance ∼19 pc. Spectroscopic distances and transverse velocities are derived for the sample. Two ∼L5 objects lie only at ∼0 pc distant. Such nearby objects are excellent targets for further study to derive their parallaxes and to search for fainter, later companions with adaptive optics and/or methane imaging.