Confirmation of One of the Coldest Known Brown Dwarfs

TL;DR

This study confirms WD 0806-661 B as the coldest directly imaged brown dwarf outside the solar system, with an estimated temperature of 300-345 K, using multi-wavelength infrared observations and color analysis.

Contribution

First direct imaging confirmation of WD 0806-661 B as the coldest known brown dwarf, with detailed infrared color measurements and temperature estimation.

Findings

WD 0806-661 B is detected at 3.6 and 4.5 microns but not in J-band.

Its colors suggest it is extremely cold, with T=300-345 K.

It is one of the coldest brown dwarfs known outside the solar system.

Abstract

Using two epochs of 4.5um images from the Infrared Array Camera (IRAC) on board the Spitzer Space Telescope, we recently identified a common proper motion companion to the white dwarf WD 0806-661 that is a candidate for the coldest known brown dwarf. To verify its cool nature, we have obtained images of this object at 3.6um with IRAC, at J with HAWK-I on the Very Large Telescope, and in a filter covering the red half of J with FourStar on Magellan. WD 0806-661 B is detected by IRAC but not HAWK-I or FourStar. From these data we measure colors of [3.6]-[4.5]=2.77+/-0.16 and J-[4.5]>7.0 (SNR<3). Based on these colors and its absolute magnitudes, WD 0806-661 B is the coldest companion directly imaged outside of the solar system and is a contender for the coldest known brown dwarf with the Y dwarf WISEP J1828+2650. It is unclear which of these two objects is colder given the available data. A comparison of its absolute magnitude at 4.5um to the predictions of theoretical spectra and evolutionary models suggests that WD 0806-661 B has T=300-345 K.