  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 and optical (R~1000) observations using
NIRSPEC and LRIS at the W.M. Keck Observatory reveal transitions of TiO, VO, K
I, Na I, Cs I, Rb I, CaH, and FeH. By comparing these features in late-type
giants and in old field dwarfs we show that they are sensitive to the gravity
(g = GM/R^2) of the object. Using low-gravity spectral signatures as age
indicators, we observed and analyzed J-band and optical spectra of two young
brown dwarfs, G 196-3B (20-300 Myr) and KPNO Tau-4 (1-2 Myr), and two possible
low mass brown dwarfs in the sigma Orionis cluster (3-7 Myr). We report the
identification of the phi bands of TiO near 1.24 microns and the A-X band of VO
near 1.18 microns together with extremely weak J-band lines of K I in
KPNO-Tau4. This is the first detection of TiO and VO in the J-band in a
sub-stellar mass object. The optical spectrum of KPNO-Tau4 exhibits weak K I
and Na I lines, weak absorption by CaH, and strong VO bands, also signatures of
a lower gravity atmosphere. G 196-3B shows absorption features in both
wavelength regions like those of KPNO-Tau4 suggesting that its age and mass are
at the lower end of published estimates. Whereas sigma Ori 51 appears to be
consistent with a young sub-stellar object, sigma Ori 47 shows signatures of
high gravity most closely resembling an old L1.5/L0, and can not be a member of
the sigma Orionis cluster.
