Abstract:
Among the hundreds of brown dwarfs known, we have identified 40 late-M and L
dwarfs that exhibit conspicuous spectral features that we attribute to low
gravity, indicating both youth and low mass. Most of the sources are
suspected of being associated with the nearby, intermediate-age (10-100 Myr)
moving groups (e.g., Beta Pictoris, Tucana/Horologium) located in the
southern hemisphere. With ages less than 100 Myr but older than the
well-studied members of 1 Myr-old clusters, these juvenile brown dwarfs fill
a gap in our knowledge of brown dwarf evolution and will become important
benchmarks in the study of substellar formation, evolution, and atmospheres.
As part of a comprehensive program to study the mass and age phase space
spanned by these 40 objects (10-30 M_Jupiter, 10-100 Myr), we propose to use
24 hrs with Phoenix on Gemini-South to measure the radial velocity of 4
faint, southern candidates in order to derive their full space motions and to
ultimately determine their origin and age. The proposed observations would
complete the radial velocity component of our program.