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Autor(en) / Beteiligte
Titel
A SAMPLE OF VERY YOUNG FIELD L DWARFS AND IMPLICATIONS FOR THE BROWN DWARF LITHIUM TEST AT EARLY AGES
Ist Teil von
  • The Astrophysical journal, 2008-12, Vol.689 (2), p.1295-1326
Ort / Verlag
Bristol: IOP
Erscheinungsjahr
2008
Quelle
EZB Electronic Journals Library
Beschreibungen/Notizen
  • 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 (<100 Myr) L dwarfs the line is weaker or undetectable. We show that a weakening of lithium at lower gravities is predicted by model atmosphere calculations, an effect partially corroborated by existing observational data. Larger samples containing L dwarfs of well-determined ages are needed to further test this empirically. If verified, this result would reinforce the caveat first cited by Kirkpatrick and coworkers that the lithium test should be used with caution when attempting to confirm the substellar nature of the youngest brown dwarfs.
Sprache
Englisch
Identifikatoren
ISSN: 0004-637X
eISSN: 1538-4357
DOI: 10.1086/592768
Titel-ID: cdi_proquest_miscellaneous_743467123

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