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

March 2018 • 2018AJ....155..132Z

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

Abstract • 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.

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Patrick Lowrance

Senior Scientist