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M.R. McGovern, I.S. McLean (UCLA), J.D. Kirkpatrick (IPAC), A.J. Burgasser, L. Prato (UCLA)
Theoretical models predict that sub-stellar objects are much more luminous and hotter when very young. Consequently, deep imaging surveys of young clusters can yield very low mass sub-stellar objects that will be too faint to study once they have aged, unless they are located extremely close to the Sun. Candidate member samples of these clusters can suffer contamination from foreground and background much older field brown dwarfs. One way to distinguish between young and old brown dwarfs is to look for gravity-sensitive spectral features. We report the initial results of the Brown Dwarf Spectroscopic Survey Gravity Project, to study gravity sensitive features as indicators of youth in brown dwarfs. Low-resolution (R~2000) J-band observations using NIRSPEC at the W.M. Keck Observatory reveal transitions of TiO, VO, K I, and FeH. By comparing these features in low gravity late-type giants and in high gravity old field dwarfs we show that they are sensitive to the gravity (g = GM/R2) of the object. Using low-gravity spectral signatures as age indicators, we observed and analyzed J-band spectra of candidate brown dwarfs in \rho Ophiuchus, Taurus, Upper Scorpious, \sigma Orionis, TW Hydrae association, \alpha Persei, Pleiades as well as companions to young star and members of the field. By quantifying the variation of gravity features as a function of spectral type, we hope to create a roadmap for positively identifying young brown dwarfs as members of young clusters which is applicable to any moderate-resolution near-infrared spectra data set. This program complements a separate optical investigation with LRIS on the Keck I telescope currently in progress by team-member, Davy Kirkpatrick. By critically examining gravity-sensitive features, we are paving the path for classification in two dimensions, and refining the ability to measure both temperature and mass for identified brown dwarfs.
The author(s) of this abstract have provided an email address for comments about the abstract: mcgovern@astro.ucla.edu
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.