Observations are presented which show that LiI 6708A is detected with equivalent width of 0.53+-0.05A in the proper-motion object LP 944-20 (which is also known as BRI 0337-3535). This Li detection implies that LP 944-20 is a brown dwarf with mass between 0.057 and 0.063Mo and age between 475 and 650Myr, making it the first brown dwarf to have its mass and age precisely determined.
Cite
@article{arxiv.astro-ph/9801171,
title = {The Intermediate Age Brown Dwarf LP 944-20},
author = {C. G. Tinney},
journal= {arXiv preprint arXiv:astro-ph/9801171},
year = {2009}
}