Monday, July 20, 2015

Properties of a Pair of Juvenile Brown Dwarfs

Observations of DE0823-49 indicated that it is a system composed of a pair of brown dwarfs identified as DE0823-49A (primary) and DE0823-49B (secondary) with spectral types L1.5 ± 0.6 and L5.5 ± 1.1, respectively. Both objects orbit each other every ~248 days. The estimated effective temperatures of DE0823-49A and DE0823-49B are 2,150 ± 100 K and 1,670 ± 140 K, respectively. Models predict that both objects have masses between 0.028 to 0.063 times the Sun’s mass for DE0823-49A and between 0.018 to 0.045 times the Sun’s mass for DE0823-49B, with a mass ratio (i.e. mass of DE0823-49A relative to DE0823-49B) of 0.64 to 0.74. This places both objects in the brown dwarf mass regime and also below the lithium-burning mass limit of 0.065 times the Sun’s mass.

The age DE0823-49 is estimated to be between 80 million to 500 million years. This is consistant with the presence of lithium detected on DE0823-49A which implies it has a mass of less than 0.065 times the Sun’s mass. An object more massive that that is expected to burn away its lithium. Given that DE0823-49A is less than 0.065 times the Sun’s mass and still relatively hot, and that brown dwarfs cool gradually as they age, the age of DE0823-49A cannot exceed 500 million years. Since both DE0823-49A and DE0823-49B formed together, they should have the same age. With an age of less than 500 million years, DE0823-49 is a pair of juvenile brown dwarfs. It is also relatively nearby, located only 67.5 light years away.

Sahlmann et al. (2015), “DE0823-49 is a juvenile binary brown dwarf at 20.7 pc”, arXiv:1505.07972 [astro-ph.SR]