Using two epochs of 4.5 µm 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 3.6 µm 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 \pm 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 4.5 µm to the predictions of theoretical spectra and evolutionary models suggests that WD 0806-661 B has T _ { eff } = 300 –345 K .