DEEP z-BAND OBSERVATIONS OF THE COOLEST Y DWARF

Taisiya G. Kopytova*, Ian J. M. Crossfield, Niall R. Deacon, Wolfgang Brandner, Esther Buenzli, Amelia Bayo, Joshua E. Schlieder, Elena Manjavacas, Beth A. Biller, Derek Kopon

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

WISE J085510.83-071442.5 (hereafter, WISE 0855-07) is the coolest Y dwarf known to date and is located at a distance of 2.31 +/- 0.08 pc, giving it the fourth largest parallax of any known star or brown dwarf system. We report deep z-band observations of WISE 0855-07 using FORS2 on UT1/Very Large Telescope. We do not detect any counterpart to WISE 0855-07 in our z-band images and estimate a brightness upper limit of AB mag > 24.8 (F. <0.45 mu Jy) at 910 +/- 65 nm with 3 sigma confidence. We combine our z-band upper limit with previous near-and mid-infrared photometry to place constraints on the atmospheric properties of WISE 0855-07 via comparison to models which implement water clouds in the atmospheres of T-eff <300 K substellar objects. We find that none of the available models that implement water clouds can completely reproduce the observed spectral energy distribution of WISE 0855-07. Every model significantly disagrees with the (3.6 mu m/4.5 mu m) flux ratio and at least one other bandpass. Since methane is predicted to be the dominant absorber at 3-4 mu m, these mismatches might point to an incorrect or incomplete treatment of methane in current models. We conclude that (a) WISE0855-07 has Teff similar to 200-250 K, (b) <80% of its surface is covered by clouds, and (c) deeper observations, and improved models of substellar evolution, atmospheres, clouds, and opacities will be necessary to better characterize this object.

Original languageEnglish
Article number3
Number of pages4
JournalAstrophysical Journal
Volume797
Issue number1
DOIs
Publication statusPublished - 10 Dec 2014

Keywords

  • brown dwarfs
  • stars: individual (WISE J085510.83-071442.5)
  • stars: low-mass
  • SURVEY-EXPLORER WISE
  • BROWN DWARF
  • WATER CLOUDS
  • T-DWARFS
  • TRANSITION
  • EXOPLANETS
  • DISCOVERY
  • SPECTRA
  • STARS

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