INDICATIONS OF WATER CLOUDS IN THE COLDEST KNOWN BROWN DWARF

We present a deep near-infrared image of the newly discovered brown dwarf WISE J085510.83-071442.5 (W0855) using the FourStar imager at Las Campanas Observatory. Our detection of J3 = 24.8_−0.35^+0.53 (J _MKO = 25.0_−0.35^+0.53) at 2.6σ—or equivalently an upper limit of J3 > 23.8 (J _MKO > 24.0) at 5σ makes W0855 the reddest brown dwarf ever categorized (J _MKO – W2 = 10.984_−0.35^+0.53 at 2.6σ—or equivalently an upper limit of J _MKO – W2 > 9.984 at 5σ) and refines its position on color-magnitude diagrams. Comparing the new photometry with chemical equilibrium model atmosphere predictions, we demonstrate that W0855 is 2.7σ from models using a cloudless atmosphere and well reproduced by partly cloudy models (50%) containing sulfide and water ice clouds. Non-equilibrium chemistry or non-solar metallicity may change predictions, however using currently available model approaches, this is the first candidate outside our own solar system to have direct evidence for water clouds