||Constraining the Evolution of Brown Dwarf Binarity as a
Function of Age: A Keck LGS AO Search for Brown Dwarf and
Planetary Mass Companions to Upper Scorpius Brown Dwarfs
||448, 16th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun
||Biller, B.; Allers, K.; Liu, M.; Close, L. M.; Dupuy, T.
||We searched for binary companions to 20 brown dwarfs in Upper
Scorpius (145 pc, 5 Myr, nearest OB association)
with the facility infrared camera NIRC2
and the Laser Guide Star adaptive optics system
on the 10 m Keck II telescope.
We discovered a close companion (0.14″, 20.9±0.4 AU)
to the very low mass object SCH
From spectral deconvolution of integrated-light near-IR spectroscopy
of SCH1609 using the SpeX spectrograph (Rayner et al. 2003),
we estimate primary and secondary spectral types of
M6±0.5 and M7±1.0, corresponding to masses of
79±17 MJup and 55±25 MJup
at an age of 5 Myr and masses of 84±15 MJup and
60±25 MJup at an age of 10 Myr.
For our survey objects with spectral types
later than M8, we find an upper limit on the binary
fraction of <9% (1-σ) at separations greater than 10 AU.
We combine the results of our survey with previous surveys of Upper
Sco and similar young regions to set the strongest constraints to date
on binary fraction for young substellar objects and very low mass stars.
The binary fraction for low mass (<40 MJup) brown dwarfs in Upper Sco
is similar to that for T dwarfs in the field; for higher mass brown
dwarfs and very low mass stars, there is an excess of
medium-separation (10-50 AU
projected separation) young binaries with respect to the field. These
medium separation binaries will likely survive to late ages.