Brown dwarf photospheres are patchy: A hubble space telescope near-infrared spectroscopic survey finds frequent low-level variability

Esther Buenzli, Dániel Apai, Jacqueline Radigan, I. Neill Reid, Davin Flateau

Research output: Contribution to journalArticlepeer-review

103 Scopus citations


Condensate clouds strongly impact the spectra of brown dwarfs and exoplanets. Recent discoveries of variable L/T transition dwarfs argued for patchy clouds in at least some ultracool atmospheres. This study aims to measure the frequency and level of spectral variability in brown dwarfs and to search for correlations with spectral type. We used Hubble Space Telescope/Wide Field Camera 3 to obtain spectroscopic time series for 22 brown dwarfs of spectral types ranging from L5 to T6 at 1.1-1.7 μm for 40 minutes per object. Using Bayesian analysis, we find six brown dwarfs with confident (p > 95%) variability in the relative flux in at least one wavelength region at sub-percent precision, and five brown dwarfs with tentative (p > 68%) variability. We derive a minimum variability fraction over all covered spectral types. The fraction of variables is equal within errors for mid-L, late-L, and mid-T spectral types; for early-T dwarfs we do not find any confident variable but the sample is too small to derive meaningful limits. For some objects, the variability occurs primarily in the flux peak in the J or H band, others are variable throughout the spectrum or only in specific absorption regions. Four sources may have broadband peak-to-peak amplitudes exceeding 1%. Our measurements are not sensitive to very long periods, inclinations near pole-on and rotationally symmetric heterogeneity. The detection statistics are consistent with most brown dwarf photospheres being patchy. While multiple-percent near-infrared variability may be rare and confined to the L/T transition, low-level heterogeneities are a frequent characteristic of brown dwarf atmospheres.

Original languageEnglish (US)
Article number77
JournalAstrophysical Journal
Issue number2
StatePublished - Feb 20 2014


  • Brown dwarfs
  • Stars: atmospheres
  • Stars: low-mass

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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