Cloud Atlas: Rotational Modulations in the L/T Transition Brown Dwarf Companion HN Peg B

Yifan Zhou, Dániel Apai, Stanimir Metchev, Ben W.P. Lew, Glenn Schneider, Mark S. Marley, Theodora Karalidi, Elena Manjavacas, Luigi R. Bedin, Nicolas B. Cowan, Paulo A. Miles-Páez, Patrick J. Lowrance, Jacqueline Radigan, Adam J. Burgasser

Research output: Contribution to journalArticlepeer-review

26 Scopus citations


Time-resolved observations of brown dwarfs' rotational modulations provide powerful insights into the properties of condensate clouds in ultra-cool atmospheres. Multi-wavelength light curves reveal cloud vertical structures, condensate particle sizes, and cloud morphology, which directly constrain condensate cloud and atmospheric circulation models. We report results from Hubble Space Telescope/Wide Field Camera 3 near-infrared G141 taken in six consecutive orbits observations of HN Peg B, an L/T transition brown dwarf companion to a G0V type star. The best-fit sine wave to the 1.1-1.7 μm broadband light curve has an amplitude of 1.206% ±0.025% and period of 15.4 ±0.5 hr. The modulation amplitude has no detectable wavelength dependence except in the 1.4 μm water absorption band, indicating that the characteristic condensate particle sizes are large (>1 μm). We detect significantly (4.4σ) lower modulation amplitude in the 1.4 μm water absorption band and find that HN Peg B's spectral modulation resembles those of early T type brown dwarfs. We also describe a new empirical interpolation method to remove spectral contamination from the bright host star. This method may be applied in other high-contrast time-resolved observations with WFC3.

Original languageEnglish (US)
Article number132
JournalAstronomical Journal
Issue number3
StatePublished - Mar 2018


  • brown dwarfs
  • methods: observational
  • stars: atmospheres

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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