Proper Motions and Tangential Velocities for a Large Sample of Late-type M, L and T Dwarfs

Details Proper Motions and Tangential Velocities for a Large Sample of Late-type M, L and T Dwarfs Proper Motions and Tangential Velocities for a Large Sample of Late-type M, L and T Dwarfs

Feb 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aipc.1094..517f&link_type=abstract

COOL STARS, STELLAR SYSTEMS AND THE SUN: Proceedings of the 15th Cambridge Workshop on Cool Stars, Stellar Systems and the Sun.

Astronomy and Astrophysics

Astronomy

Low Luminosity Stars, Subdwarfs, And Brown Dwarfs, Star Formation, Fundamental Astronomy

Scientific paper

We report proper motion measurements for 427 late-type M, L and T dwarfs, 332 of which have been measured for the first time. Combining these new proper motions with previously published measurements yields a sample of 841 M7-ndashT8 dwarfs. We combined parallax measurements or calculated spectrophotometric distances and computed tangential velocities for the entire sample. We find that kinematics for the full and volume-limited 20 pc samples are consistent with those expected for the Galactic thin disk, with no significant differences between late-type M, L, and T dwarfs. Applying an age-velocity relation we conclude that the average kinematic age of the 20 pc sample of ultracool dwarfs is older than recent kinematic estimates and more consistent with age results calculated with population synthesis models. We isolate subsets of the entire sample, including low surface-gravity dwarfs, unusually blue L dwarfs, and photometric outliers in J-Ks color and investigate their kinematics. We find that the spectroscopically distinct class of unusually blue L dwarfs has kinematics clearly consistent with old age, implying that high surface-gravity and/or low metallicity may be relevant to their spectral properties. The low surface-gravity dwarfs are kinematically younger than the overall population, and the kinematics of the red and blue ultracool dwarfs suggest ages that are younger and older than the full sample, respectively.

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