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Cloud Atlas: Weak Color Modulations Due to Rotation in the Planetary-mass Companion GU Psc b and 11 Other Brown Dwarfs

Lew, Ben W. P. and Apai, Dániel and Zhou, Yifan and Radigan, Jacqueline and Marley, Mark and Schneider, Glenn and Cowan, Nicolas B. and Miles-Páez, Paulo A. and Manjavacas, Elena and Karalidi, Theodora and Bedin, L. R. and Lowrance, Patrick J. and Burgasser, Adam J. (2020) Cloud Atlas: Weak Color Modulations Due to Rotation in the Planetary-mass Companion GU Psc b and 11 Other Brown Dwarfs. Astronomical Journal, 159 (3). Art. No. 125. ISSN 1538-3881. doi:10.3847/1538-3881/ab5f59.

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Among the greatest challenges in understanding ultracool brown dwarf and exoplanet atmospheres is the evolution of cloud structure as a function of temperature and gravity. In this study, we present the rotational modulations of GU Psc b—a rare mid-T spectral type planetary-mass companion at the end of the L/T spectral type transition. Based on the Hubble Space Telescope/WFC3 1.1–1.67 μm time-series spectra, we observe a quasi-sinusoidal light curve with a peak-to-trough flux variation of 2.7% and a minimum period of 8 h. The rotation-modulated spectral variations are weakly wavelength-dependent, or largely gray between 1.1 and 1.67 μm. The gray modulations indicate that heterogeneous clouds are present in the photosphere of this low-gravity mid-T dwarf. We place the color and brightness variations of GU Psc b in the context of rotational modulations reported for mid-L to late-T dwarfs. Based on these observations, we report a tentative trend: mid-to-late T dwarfs become slightly redder in J − H color with increasing J-band brightness, while L dwarfs become slightly bluer with increasing brightness. If this trend is verified with more T-dwarf samples, it suggests that in addition to the mostly gray modulations, there is a second-order spectral-type dependence on the nature of rotational modulations.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Lew, Ben W. P.0000-0003-1487-6452
Apai, Dániel0000-0003-3714-5855
Zhou, Yifan0000-0003-2969-6040
Radigan, Jacqueline0000-0002-6732-3651
Marley, Mark0000-0002-5251-2943
Schneider, Glenn0000-0002-4511-5966
Cowan, Nicolas B.0000-0001-6129-5699
Miles-Páez, Paulo A.0000-0003-2446-8882
Manjavacas, Elena0000-0003-0192-6887
Karalidi, Theodora0000-0001-7356-6652
Bedin, L. R.0000-0003-4080-6466
Lowrance, Patrick J.0000-0001-8014-0270
Burgasser, Adam J.0000-0002-6523-9536
Additional Information:© 2020. The American Astronomical Society. Received 2019 October 13; revised 2019 December 1; accepted 2019 December 4; published 2020 February 25. We would like to thank the anonymous referee for constructive comments and suggestions that significantly improve this paper. We would like to thank Esther Buenzli for providing the time-resolved spectra of Luhman 16b. Support for program number HST-GO-14241 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. This research has benefited from the Montreal Brown Dwarf and Exoplanet Spectral Library, maintained by Jonathan Gagné and the SpeX Prism Spectral Libraries, maintained by Adam Burgasser at This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. This work has made use of data from the European Space Agency (ESA) mission Gaia (, processed by the Gaia Data Processing and Analysis Consortium (DPAC, Funding for DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Gaia Multilateral AgreementUNSPECIFIED
Subject Keywords:Brown dwarfs ; Exoplanet atmospheres ; Planetary atmospheres ; Exoplanet atmospheric variability ; T dwarfs
Issue or Number:3
Classification Code:Unified Astronomy Thesaurus concepts: Brown dwarfs (185); Exoplanet atmospheres (487); Planetary atmospheres (1244); Exoplanet atmospheric variability (2020); T dwarfs (1679)
Record Number:CaltechAUTHORS:20200225-135943829
Persistent URL:
Official Citation:Ben W. P. Lew et al 2020 AJ 159 125
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:101549
Deposited By: George Porter
Deposited On:26 Feb 2020 15:53
Last Modified:16 Nov 2021 18:03

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