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Activity and Kinematics of M and L Dwarfs

Abstract

I discuss observations of two traditional age indicators, chromospheric activity and kinematics, in late-M and L dwarfs near the hydrogen-burning limit. The frequency and strength of chromospheric activity disappears rapidly as a function of temperature over spectral types M8-L4. There is evidence that young late-M and L dwarfs have weaker activity than older ones, the opposite of the traditional stellar age-activity relation. The kinematics of L dwarfs confirm that lithium L dwarfs are younger than non-lithium dwarfs.Comment: to appear in proceedings of Ultracool Dwarf Stars: Surveys, Properties and Spectral Classification (Lecture Notes in Physics), eds. Jones and Steele. 12 page

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