Zones, spots, and planetary-scale waves beating in brown dwarf atmospheres

Beating bands in substellar atmospheres Brown dwarfs are objects with masses that are between those of large planets and small stars. They share many features with gas giant planets, particularly conditions in their atmospheres. Apai et al. analyzed how the infrared brightness of three brown dwarfs changes over time. Several perplexing features can be explained if bands of clouds rotating within their atmospheres generate beat patterns. Such bands are seen in optical images of Jupiter but best match infrared images of Neptune. The results shed light on the atmospheric physics of brown dwarfs and gas giant planets around the Sun and other stars. Science, this issue p. 683 Infrared monitoring of brown dwarf stars shows evidence for bands of clouds rotating within their 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.

[1]  USA,et al.  Fast-evolving weather for the coolest of our two new substellar neighbours , 2013, 1304.0481.

[2]  Andrew S. Ackerman,et al.  Precipitating Condensation Clouds in Substellar Atmospheres , 2001, astro-ph/0103423.

[3]  Daniel Apai,et al.  HST SPECTRAL MAPPING OF L/T TRANSITION BROWN DWARFS REVEALS CLOUD THICKNESS VARIATIONS , 2013, 1303.4151.

[4]  Ingalls,et al.  SPITZER SPACE TELESCOPE MID-IR LIGHT CURVES OF NEPTUNE , 2016, 1608.07198.

[5]  R. Jayawardhana,et al.  STRONG BRIGHTNESS VARIATIONS SIGNAL CLOUDY-TO-CLEAR TRANSITION OF BROWN DWARFS , 2014, 1404.3247.

[6]  Nicolas B. Cowan,et al.  Inverting Phase Functions to Map Exoplanets , 2008, 0803.3622.

[7]  D. Apai,et al.  MAPS OF EVOLVING CLOUD STRUCTURES IN LUHMAN 16AB FROM HST TIME-RESOLVED SPECTROSCOPY , 2016, 1605.01682.

[8]  B. Macintosh,et al.  Images of a fourth planet orbiting HR 8799 , 2010, Nature.

[9]  Jean-Luc Beuzit,et al.  Direct imaging discovery of a Jovian exoplanet within a triple-star system , 2016, Science.

[10]  H. Hammel,et al.  Seeing double at Neptune's south pole , 2010, 1003.3240.

[11]  G. Schwarz.  Estimating the Dimension of a Model , 1978 .

[12]  G. Orton,et al.  Neptune’s global circulation deduced from multi-wavelength observations , 2014 .

[13]  Michael H. Wong,et al.  NEPTUNE’S DYNAMIC ATMOSPHERE FROM KEPLER K2 OBSERVATIONS: IMPLICATIONS FOR BROWN DWARF LIGHT CURVE ANALYSES , 2015, The Astrophysical journal.

[14]  Patrick J. Lowrance,et al.  EXTRASOLAR STORMS: PRESSURE-DEPENDENT CHANGES IN LIGHT-CURVE PHASE IN BROWN DWARFS FROM SIMULTANEOUS HST AND SPITZER OBSERVATIONS , 2016, 1605.02708.

[15]  Etienne Artigau,et al.  LARGE-AMPLITUDE VARIATIONS OF AN L/T TRANSITION BROWN DWARF: MULTI-WAVELENGTH OBSERVATIONS OF PATCHY, HIGH-CONTRAST CLOUD FEATURES , 2012, 1201.3403.

[16]  S. Seager,et al.  Clouds and chemistry: Ultracool dwarf atmospheric properties from optical and infrared colors , 2002 .

[17]  Xi Zhang,et al.  ATMOSPHERIC CIRCULATION OF BROWN DWARFS: JETS, VORTICES, AND TIME VARIABILITY , 2014, 1403.2143.

[18]  I. Reid,et al.  CLOUD STRUCTURE OF THE NEAREST BROWN DWARFS: SPECTROSCOPIC VARIABILITY OF LUHMAN 16AB FROM THE HUBBLE SPACE TELESCOPE , 2014, 1411.0003.

[19]  R. Street,et al.  A MONITORING CAMPAIGN FOR LUHMAN 16AB. I. DETECTION OF RESOLVED NEAR-INFRARED SPECTROSCOPIC VARIABILITY , 2014, 1402.2342.

[20]  G. Schubert,et al.  Thermal structure of Jupiter's atmosphere near the edge of a 5‐μm hot spot in the north equatorial belt , 1998 .

[21]  Daniel Foreman-Mackey,et al.  emcee: The MCMC Hammer , 2012, 1202.3665.

[22]  Peter Plavchan,et al.  WEATHER ON OTHER WORLDS. II. SURVEY RESULTS: SPOTS ARE UBIQUITOUS ON L AND T DWARFS , 2014, 1411.3051.

[23]  D. Apai,et al.  AEOLUS: A MARKOV CHAIN MONTE CARLO CODE FOR MAPPING ULTRACOOL ATMOSPHERES. AN APPLICATION ON JUPITER AND BROWN DWARF HST LIGHT CURVES , 2015, 1510.04251.

[24]  D. Rubin,et al.  Inference from Iterative Simulation Using Multiple Sequences , 1992 .

[25]  David Lafreniere,et al.  PHOTOMETRIC VARIABILITY OF THE T2.5 BROWN DWARF SIMP J013656.5+093347: EVIDENCE FOR EVOLVING WEATHER PATTERNS , 2009, 0906.3514.

[26]  Bernd Freytag,et al.  WEATHER ON THE NEAREST BROWN DWARFS: RESOLVED SIMULTANEOUS MULTI-WAVELENGTH VARIABILITY MONITORING OF WISE J104915.57−531906.1AB , 2013, 1310.5144.

[27]  Nicolas B. Cowan,et al.  Light curves of stars and exoplanets: estimating inclination, obliquity and albedo , 2013, 1304.6398.

[28]  J. Akrman,et al.  Dyeing behavior of polypropylene blend fiber. III. Effect of drawing on dyeability , 1999 .

[29]  I. Reid,et al.  BROWN DWARF PHOTOSPHERES ARE PATCHY: A HUBBLE SPACE TELESCOPE NEAR-INFRARED SPECTROSCOPIC SURVEY FINDS FREQUENT LOW-LEVEL VARIABILITY , 2013, 1312.5294.

[30]  William B. Hubbard,et al.  Atmospheric confinement of jet streams on Uranus and Neptune , 2013, Nature.

[31]  Yohai Kaspi,et al.  ATMOSPHERIC DYNAMICS OF BROWN DWARFS AND DIRECTLY IMAGED GIANT PLANETS , 2012, 1210.7573.

[32]  I. Reid,et al.  VERTICAL ATMOSPHERIC STRUCTURE IN A VARIABLE BROWN DWARF: PRESSURE-DEPENDENT PHASE SHIFTS IN SIMULTANEOUS HUBBLE SPACE TELESCOPE–SPITZER LIGHT CURVES , 2012, 1210.6654.