Ultracool dwarfs with spectra in LAMOST DR7

All these ultracool dwarfs are within 360 pc, with the Gaia G magnitude brighter than ~19.2mag. Studying the spectra and checking their stellar parameters (Teff, logg and [M/H]) derived with the LAMOST pipeline, we found their cool red nature and their metallicity consistent with being Galaxy thin disk objects.

Furthermore, 77 of them show lithium absorption line at 6708{AA} indicating their young ages and substellar nature. Kinematics obtained through LAMOST radial velocities combining with the proper motion and parallax from Gaia EDR3, also suggest the majority of our targets are thin disk objects. Kinematic ages are estimated through the relationship between the velocity dispersion and the average age for a certain population.