Brown Dwarf Kinematics Project (BDKP. III. Parallaxes for 70 Ultracool Dwarfs).

摘要

We report parallax measurements for 70 ultracool dwarfs (UCDs) including 11 late-M, 32 L, and 27 T dwarfs. In this sample, 14 M and L dwarfs exhibit low surface gravity features, 6 are close binary systems, and 2 are metal-poor subdwarfs. We combined our new measurements with 114 previously published UCD parallaxes and optical mid-IR photometry to examine trends in spectral-type/absolute magnitude, and color color diagrams. We report new polynomial relations between spectral type and MJHK. Including resolved L/T transition binaries in the relations, we find no reason to differentiate between a bright (unresolved binary) and a faint (single source) sample across the L/T boundary. Isolating early T dwarfs, we find that the brightening of T0 T4 sources is prominent inMJ where there is a 1.2-1.4 mag difference.