Astrometric monitoring of the nearby early-L dwarf DE0823 - 49 has revealed a low-mass companion in a 248-day orbit that was announced in an earlier work .
Here , we present new astrometric and spectroscopic observations that allow us to characterise the system in detail .
The optical spectrum shows Li i -absorption indicative of a young age and/or substellar mass for the primary component .
The near-infrared spectrum is best reproduced by a binary system of brown dwarfs with spectral types of L1.5 + L5.5 and effective temperatures of 2150 \pm 100 K and 1670 \pm 140 K. To conform with the photocentric orbit size measured with astrometry and the current understanding of substellar evolution , the system must have an age in the 80–500 Myr range .
Evolutionary models predict component masses in the ranges of M _ { 1 } \simeq 0.028 - 0.063 M _ { \sun } and M _ { 2 } \simeq 0.018 - 0.045 M _ { \sun } with a mass ratio of q \simeq 0.64 - 0.74 .
Multi-epoch radial velocity measurements unambiguously establish the three-dimensional orbit of the system and allow us to investigate its kinematic properties .
DE0823 - 49 emerges as a rare example of a nearby brown dwarf binary with orbit , component properties , and age that are characterised well .
It is a juvenile resident of the solar neighbourhood , but does not appear to belong to a known young association or moving group .