A SAMPLE OF VERY YOUNG FIELD L DWARFS AND IMPLICATIONS FOR THE BROWN DWARF LITHIUM TEST AT EARLY AGES

• Published in: The Astrophysical journal 2008-12, Vol.689 (2), p.1295-1326
• Main Authors: KIRKPATRICK, J. Davy, CRUZ, Kelle L, HILLENBRAND, Lynne A, STAUFFER, John R, BARMAN, Travis S, BURGASSER, Adam J, LOOPER, Dagny L, TINNEY, C. G, GELINO, Christopher R, LOWRANCE, Patrick J, LIEBERT, James, CARPENTER, John M
• Format: Article
• Language: English
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1086/592768

Using a large sample of optical spectra of late-type dwarfs, we identify a subset of late-M through L field dwarfs that, because of the presence of low-gravity features in their spectra, are believed to be unusually young. From a combined sample of 303 field L dwarfs, we find observationally that [image] are younger than 100 Myr. This percentage is in agreement with theoretical predictions once observing biases are taken into account. We find that these young L dwarfs tend to fall in the southern hemisphere and may be previously unrecognized, low-mass members of nearby, young associations like Tucana-Horologium, TW Hydrae, beta Pictoris, and AB Doradus. We use a homogeneously observed sample of [image]150 optical spectra to examine lithium strength as a function of L/T spectral type and further corroborate the trends noted by Kirkpatrick and coworkers. We use our low-gravity spectra to investigate lithium strength as a function of age. The data weakly suggest that for early- to mid-L dwarfs the line strength reaches a maximum for a [image] Myr, whereas for much older (few Gyr) and much younger (