HST SPECTRAL MAPPING OF L/T TRANSITION BROWN DWARFS REVEALS CLOUD THICKNESS VARIATIONS

By D. Apai, Jacqueline Radigan, E. Buenzli, Adam Burrows, I. Neill Reid, R. Jayawardhana. 2013

145 citations recorded by the source corpus.

Most directly imaged giant exoplanets are fainter than brown dwarfs with similar spectra. To explain their relative underluminosity, unusually cloudy atmospheres have been proposed. However, with multiple parameters varying between any two objects, it remained difficult to observationally test this idea. We present a new method, sensitive time-resolved Hubble Space Telescope near-infrared spectroscopy, to study two rotating L/T transition brown dwarfs (2M2139 and SIMP0136). The observations provide spatially and spectrally resolved mapping of the cloud decks of the brown dwarfs. The data allow the study of cloud structure variations while other parameters are unchanged. We find that both brown dwarfs display variations of identical nature: J- and H-band brightness variations with minimal color and spectral changes. Our light curve models show that even the simplest surface brightness distributions require at least three elliptical spots. We show that for each source the spectral changes can be reproduced with a linear combination of only two different spectra, i.e., the entire surface is covered by two distinct types of regions. Modeling the color changes and spectral variations together reveal patchy cloud covers consisting of a spatially heterogeneous mix of low-brightness, low-temperature thick clouds and brighter, thin, and warm clouds. We show that the same thick cloud patches seen in our varying brown dwarf targets, if extended to the entire photosphere, predict near-infrared colors/magnitudes matching the range occupied by the directly imaged exoplanets that are cooler and less luminous than brown dwarfs with similar spectral types. This supports the models in which thick clouds are responsible for the near-infrared properties of these “underluminous” exoplanets.

Subfields: Astronomy and Astrophysics, Instrumentation, Statistical and Nonlinear Physics

View Paper: https://www.semanticscholar.org/paper/2166d1302f2fb169f044ff5eab106e7fa9e718fa

How researchers see this paper

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In Astronomy and Astrophysics

1. N. Madhusudhan
2. V. Parmentier
3. M. Marley
4. M. Line
5. A. Burgasser
6. Laura Kreidberg
7. Jon Fortney
8. T. Robinson

In Instrumentation

1. V. Parmentier
2. M. Line
3. M. Marley
4. N. Madhusudhan
5. Laura Kreidberg
6. A. Burgasser
7. Th. Henning
8. É. Artigau

In Statistical and Nonlinear Physics

1. V. Parmentier
2. M. Line
3. Laura Kreidberg
4. Th. Henning
5. T. Robinson
6. D. Apai
7. M. Marley
8. S. Metchev

Citations in the corpus

• Retrieving scattering clouds and disequilibrium chemistry in the atmosphere of HR 8799e (2020, background): “Given the prevalence of variability of, especially, L-T dwarf transition objects (see, e.g., Apai et al. 2013; Crossfield 2014), such a heterogeneous cloud cover could be expected for the HR 8799 planets.”
• On the Cool Side: Modeling the Atmospheres of Brown Dwarfs and Giant Planets (2014, background): “Indeed, a variety of patchy cloud models have demonstrated that, in many cases, observed variability can be explained by changes in cloud distribution and thickness (Marley et al. 2010; Apai et al. 2013; Burgasser et al. 2014; Morley et al. 2014a).”
• THE INFLUENCE OF NONUNIFORM CLOUD COVER ON TRANSIT TRANSMISSION SPECTRA (2015, background): “…are presumed to happen in Brown dwarf atmospheres (Burgasser et al. 2002; Marley et al. 2010; Zhang & Showman 2014), where observations are strongly suggestive of non-uniform cloud cover (Buenzli et al. 2012;14; Radigan et al. 2012;14; Crossfield et al. 2014; Apai et al. 2013; Metchev et al. 2015).”
• WEATHER ON OTHER WORLDS. II. SURVEY RESULTS: SPOTS ARE UBIQUITOUS ON L AND T DWARFS (2014, background): “Rather than representing two distinct brown dwarf components, the composite spectrum may instead be revealing the two-temperature nature of the photosphere of a single object: e.g., through a combination of regions with thick clouds and regions with thin clouds (Apai et al. 2013).”