Zones, spots, and planetary-scale waves beating in brown dwarf atmospheres
Brown dwarfs are massive analogs of extrasolar giant planets and may host types of atmospheric circulation not seen in the solar system. We analyzed a long-term Spitzer Space Telescope infrared monitoring campaign of brown dwarfs to constrain cloud cover variations over a total of 192 rotations. The infrared brightness evolution is dominated by beat patterns caused by planetary-scale wave pairs and by a small number of bright spots. The beating waves have similar amplitudes but slightly different apparent periods because of differing velocities or directions. The power spectrum of intermediate-temperature brown dwarfs resembles that of Neptune, indicating the presence of zonal temperature and wind speed variations. Our findings explain three previously puzzling behaviors seen in brown dwarf brightness variations.
© 2017 American Association for the Advancement of Science. 14 February 2017; accepted 25 July 2017. Individual author contributions are listed in the supplementary materials. We acknowledge discussions with G. Mulders, V. Parmentier, and X. Zhang on atmospheric dynamics and the interpretation of our observations. This work is part of the Spitzer Cycle-9 Exploration Program "Extrasolar Storms" and based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory (JPL), California Institute of Technology, under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/California Institute of Technology. Support for the Hubble Space Telescope GO program 13176 was provided by Universities for Research in Astronomy, under NASA contract NAS5-26555. This research has benefitted from the SpeX Prism Spectral Libraries, maintained by A.J.B. at http://pono.ucsd.edu/~adam/browndwarfs/spexprism, and the M, L, T, and Y dwarf compendium at http://DwarfArchives.org. This research benefitted from the workshop "Solving the Exocartography Inverse Problem" held at the International Space Science Institute in Bern. The results reported here benefitted from collaborations and/or information exchange within NASA's Nexus for Exoplanet System Science (NExSS) research coordination network sponsored by NASA's Science Mission Directorate. An allocation of computer time from the University of Arizona Research Computing High Performance Computing and High Throughput Computing (HTC) is gratefully acknowledged. A.J.B. acknowledges funding support from the National Science Foundation under award AST-1517177. The raw observations are available from the Spitzer Heritage Archive at http://sha.ipac.caltech.edu under program 90063. Light curves for all of our targets, along with our model fits for each, are included in the supplementary file Data S1. Our adapted version of the Aeolus software is available at https://github.com/Dot83/Aeolus.