The Ultra Cool Brown Dwarf Companion of WD 0806-661: Age, Mass, and Formation Mechanism

TL;DR

This study identifies and characterizes a very cool brown dwarf companion to WD 0806-661, estimating its mass and temperature, and discusses its formation mechanism based on observational limits and theoretical models.

Contribution

It provides the first observational constraints on the properties of a very cool brown dwarf companion and suggests its formation via Jeans-mass fragmentation.

Findings

Brown dwarf companion has J-[4.5]>4.95, making it the reddest known.

Estimated mass <10-13 Jupiter masses, temperature <400 K.

Substellar companions of similar mass are found at various orbital distances.

Abstract

We have combined multi-epoch images from the Infrared Side Port Imager on the CTIO 4-meter telescope to derive a 3-sigma 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 Jupiter masses and temperature <400 K, 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 Jupiter masses) are distributed over a wide range of semi-major axes, which suggests that giant planet and low-mass brown dwarf formation overlap in this mass range.