Indications of Water Clouds in the Coldest Known Brown Dwarf

TL;DR

This paper reports the discovery of water cloud indications in the coldest known brown dwarf, WISE J085510.83-071442.5, using deep near-infrared imaging and model comparisons, marking the first direct evidence of water clouds outside our solar system.

Contribution

It provides the first observational evidence of water clouds in an extrasolar brown dwarf through photometry and model analysis, refining understanding of atmospheric composition in such objects.

Findings

W0855 is the reddest brown dwarf ever categorized.

Photometry aligns with partly cloudy models containing sulfide and water ice clouds.

First candidate outside our solar system with direct evidence for water clouds.

Abstract

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+0.33 -0.53 (J_MKO=25.0+0.33-0.53) at 2.6sigma -- or equivalently an upper limit of J3 > 23.8 (J_MKO > 24.0) at 5sigma makes W0855 the reddest brown dwarf ever categorized (J_MKO - W2 = 10.984+0.33 - 0.53 at 2.6sigma -- or equivalently an upper limit of J_MKO - W2 > 9.984 at 5sigma) and refines its position on color magnitude diagrams. Comparing the new photometry with chemical equilibrium model atmosphere predictions, we demonstrate that W0855 is 4.5sigma 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.