The Collapse of the Wien Tail in the Coldest Brown Dwarf? Hubble Space Telescope Near-Infrared Photometry of WISE J085510.83-071442.5

We present Hubble Space Telescope (HST) near-infrared photometry of the coldest known brown dwarf, WISE J085510.83−071442.5 (WISE 0855−0714). WISE 0855−0714 was observed with the Wide Field Camera 3 (WFC3) on board HST using the F105W, F125W, and F160W filters, which approximate the Y, J, and H near-infrared bands. WISE 0855−0714 is undetected at F105W with a corresponding 2σ magnitude limit of ~26.9. We marginally detect WISE 0855−0714 in the F125W images (S/N ~ 4), with a measured magnitude of 26.41 ± 0.27, more than a magnitude fainter than the J-band magnitude reported by Faherty et al. WISE J0855−0714 is clearly detected in the F160W band, with a magnitude of 23.86 ± 0.03, the first secure detection of WISE 0855−0714 in the near-infrared. Based on these data, we find that WISE 0855−0714 has extremely red F 105W - F125W and F125W - F160W colors relative to other known Y dwarfs. We find that when compared to the models of Saumon et al. and Morley et al., the F105W -F125W and F125W - F160W colors of WISE 0855−0714 cannot be accounted for simultaneously. These colors likely indicate that we are seeing the collapse of flux on the Wien tail for this extremely cold object