The ultra cool brown dwarf companion of WD 0806-661B: Age, mass, and formation mechanism

Abstract

We have combined multi-epoch images from the Infrared Side Port Imager on the CTIO 4 m telescope to derive a 3σ limit of J = 21.7 for the ultra cool brown dwarf companion to WD 0806-661 (GJ 3483). We find that J - [4.5] > 4.95, redder than any other brown dwarf known to date. With theoretical evolutionary models and ages 1.5-2.7 Gyr, we estimate the brown dwarf companion to have mass <10-13 MJup and temperature ≲ 400K, providing evidence that this is among the coolest brown dwarfs currently known. The range of masses for this object is consistent with that anticipated from Jeans-mass fragmentation and we present this as the likely formation mechanism. However, we find that substellar companions of similar mass (∼7-17 MJup) are distributed over a wide range of semimajor axes, which suggests that giant planet and low-mass brown dwarf formation overlap in this mass range. © 2011. The American Astronomical Society. All rights reserved.