Roaring Storms in the Planetary-Mass Companion VHS 1256-1257 b: Hubble Space Telescope Multi-epoch Monitoring Reveals Vigorous Evolution in an Ultra-cool Atmosphere

Abstract

Photometric and spectral variability of brown dwarfs probes heterogeneous temperature and cloud distribution and traces the atmospheric circulation patterns. We present a new 42-hr Hubble Space Telescope (HST) Wide Field Camera 3 G141 spectral time series of VHS 1256$-$1257 b, a late L-type planetary-mass companion that has been shown to have one of the highest variability amplitudes among substellar objects. The light curve is rapidly evolving and best-fit by a combination of three sine waves with different periods and a linear trend. The amplitudes of the sine waves and the linear slope vary with wavelength, and the corresponding spectral variability patterns match the predictions by models invoking either heterogeneous clouds or thermal profile anomalies. Combining these observations with previous HST monitoring data, we find that the peak-to-valley flux difference is $33\pm 2$% with an even higher amplitude reaching 38% in the $J$ band, the highest amplitude ever observed in a substellar object. The observed light curve can be explained by maps that are composed of zonal waves, spots, or a mixture of the two. Distinguishing the origin of rapid light curve evolution requires additional long-term monitoring. Our findings underscore the essential role of atmospheric dynamics in shaping brown dwarf atmospheres and highlight VHS 1256$-$1257 b as one of the most favorable targets for studying atmospheres, clouds, and atmospheric circulation of planets and brown dwarfs.

Accepted for publicaton in AJ. 18 pages main text, 13 figures

References in corpus (40)

• Array Programming with NumPy
• Direct Imaging of Multiple Planets Orbiting the Star HR 8799
• The generalised Lomb-Scargle periodogram. A new formalism for the floating-mean and Keplerian periodograms
• A comparison of chemistry and dust cloud formation in ultracool dwarf model atmospheres
• Discovery of a young planetary mass companion to the nearby M dwarf VHS J125601.92-125723.9
• Vertical Atmospheric Structure in a Variable Brown Dwarf: Pressure-dependent Phase Shifts in Simultaneous Hubble Space Telescope-Spitzer Light Curves
• Atmospheric Dynamics of Hot Giant Planets and Brown Dwarfs
• A Volume-Limited Sample of Ultracool Dwarfs. I. Construction, Space Density, and a Gap in the L/T Transition
• Cloud busting: enstatite and quartz clouds in the atmosphere of 2M2224-0158
• The Viewing Geometry of Brown Dwarfs Influences Their Observed Colours and Variability Properties
• Observations of Disequilibrium CO Chemistry in the Coldest Brown Dwarfs
• Atmospheric Circulation of Brown Dwarfs: Jets, Vortices, and Time Variability
• Let the Great World Spin: Revealing the Stormy, Turbulent Nature of Young Giant Exoplanet Analogs with the Spitzer Space Telescope
• Atmospheric circulation of brown dwarfs and directly imaged exoplanets driven by cloud radiative feedback: effects of rotation
• Spectral Variability from the Patchy Atmospheres of T and Y Dwarfs
• Temperature Fluctuations as a Source of Brown Dwarf Variability
• Atmospheric circulation of brown dwarfs and directly imaged exoplanets driven by cloud radiative feedback: global and equatorial dynamics
• Cloud structure of the nearest brown dwarfs: Spectroscopic variability of Luhman 16AB from the Hubble Space Telescope
• Cloud Atlas: Discovery of Patchy Clouds and High-amplitude Rotational Modulations In a Young, Extremely Red L-type Brown Dwarf
• Spitzer Variability Properties of Low-Gravity L Dwarfs
• HST Rotational Spectral Mapping of Two L-Type Brown Dwarfs: Variability In and Out of Water Bands Indicates High-Altitude Haze Layers
• Spectral Variability of VHS J1256-1257 b from 1 to 5 $\mu$m
• Weather on Other Worlds. V. The Three Most Rapidly Rotating Ultra-Cool Dwarfs
• Strong Near-Infrared Spectral Variability of the Young Cloudy L Dwarf Companion VHS J1256-1257 b
• The JWST Early Release Science Program for the Direct Imaging & Spectroscopy of Exoplanetary Systems
• Planets Around Low-Mass Stars (PALMS). VI. Discovery of a Remarkably Red Planetary-Mass Companion to the AB Dor Moving Group Candidate 2MASS J22362452+4751425
• TESS Observations of the Luhman 16AB Brown Dwarf System: Rotational Periods, Lightcurve Evolution, and Zonal Circulation
• The Second Discovery from the COol Companions ON Ultrawide orbiTS (COCONUTS) Program: A Cold Wide-Orbit Exoplanet around a Young Field M Dwarf at 10.9 pc
• Cloud Atlas: Discovery of Rotational Spectral Modulations in a Low-mass, L-type Brown Dwarf Companion to a Star
• A High-Contrast Search for Variability in HR 8799bc with VLT-SPHERE
• Cloud Atlas: High-Contrast Time-Resolved Observations of Planetary-Mass Companions
• Cloud Atlas: Weak color modulations due to rotation in the planetary-mass companion GU Psc b and 11 other brown dwarfs
• Detection of new strongly variable brown dwarfs in the L/T transition
• Rotational spectral modulation of cloudless atmospheres for L/T Brown Dwarfs and Extrasolar Giant Planets
• Atmospheric Monitoring and Precise Spectroscopy of the HR 8799 Planets with SCExAO/CHARIS
• Cloud Atlas: Unraveling the vertical cloud structure with the time-series spectrophotometry of an unusually red brown dwarf
• Thermal Infrared Imaging and Atmospheric Modeling of VHS J125601.92-125723.9 b: Evidence for Moderately Thick Clouds and Equilibrium Carbon Chemistry in a Hierarchical Triple System
• Modeling Polarization Signals from Cloudy Brown Dwarfs: Luhman 16 A and B in Three Dimensions
• A Unified Spectroscopic and Photometric Model to Infer Surface Inhomogeneity: Application to Luhman 16B
• Detection of photometric variability in the very low-mass binary VHS J1256-1257AB using TESS and Spitzer

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• A Near-infrared Variability Survey of Young Planetary-mass Objects
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• Exploring the directly imaged HD 1160 system through spectroscopic characterization and high-cadence variability monitoring
• Mapping the Skies of Ultracool Worlds: Detecting Storms and Spots with Extremely Large Telescopes
• X-SHYNE: X-Shooter spectra of young exoplanet analogs II. Presentation and analysis of the full library
• Large-amplitude Variability Driven by Giant Dust Storms on a Planetary-mass Companion
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• Disentangling auroral, cloud and magnetic spot driven variability in three early L-dwarfs with HST/WFC3
• Next-generation Exo-REM atmospheric models: application to VHS 1256 b to emulate patchy clouds