Disentangling auroral, cloud and magnetic spot driven variability in three early L-dwarfs with HST/WFC3

Abstract

Variability monitoring provides an unparalleled insight into the atmospheric processes of brown dwarfs and directly imaged exo-planets. Inhomogeneous clouds, aurorae and magnetic spots have all been postulated as potential drivers of variability. While objects at the L/T transition have had their variability studied extensively, the variability of early L-dwarfs remains an understudied region of the parameter space. We use observations from the Hubble Space Telescope in the near-infrared, using WFC3/G141 to disentangle the drivers of variability in three known variable early L-dwarfs: 2MASS J1721039+334415, 2MASS J00361617+1821104 and 2MASS J19064801+4011089. We find that all three objects exhibit significant variability at all wavelengths, with white-light amplitudes of 0.53-1.41 %. We find that their colour variations are brighter and bluer compared to later spectral types, except for 2MASSJ19064801+4011089 which exhibits largely grey variations. We report a new period for 2MASS J1721039+334415, of 4.9^{+0.4}_{-0.2} hours. We find evidence of long term light curve stability in each object, which may indicate the presence of long lived features on their surfaces. We create a flexible modelling framework to model three potential drivers of variability: clouds, aurorae and magnetic spots. We fit our models to the spectral variability amplitude from 1.1-1.67 μm of each object. We find that changing cloud properties or magnetic spots are the most likely drivers of variability in each object. Auroral models do not reproduce the variability within the HST wavelengths, however future observations at longer wavelengths that probe higher in the atmosphere may be more sensitive to auroral effects. This work provides a foundation for future variability studies of early L-dwarfs and directly imaged exoplanets to disentangle auroral, cloud and magnetic spot driven variability.

22 pages, 18 figures

References in corpus (83)

• Astropy: A Community Python Package for Astronomy
• emcee: The MCMC Hammer
• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• Binary companions of evolved stars in APOGEE DR14: Search method and catalog of ~5,000 companions
• MultiNest: an efficient and robust Bayesian inference tool for cosmology and particle physics
• X-ray spectral modelling of the AGN obscuring region in the CDFS: Bayesian model selection and catalogue
• Fast and scalable Gaussian process modeling with applications to astronomical time series
• The Infrared Telescope Facility (IRTF) Spectral Library: Cool Stars
• ExoMol molecular line lists XXX: a complete high-accuracy line list for water
• petitRADTRANS: a Python radiative transfer package for exoplanet characterization and retrieval
• A probable giant planet imaged in the Beta Pictoris disk
• Meeting the Cool New Neighbors V: A 2MASS-Selected Sample of Ultracool Dwarfs
• The Transit Light Source Effect: False Spectral Features and Incorrect Densities for M-dwarf Transiting Planets
• L and T Dwarf Models and the L to T Transition
• Fundamental Parameters and Spectral Energy Distributions of Young and Field Age Objects with Masses Spanning the Stellar to Planetary Regime
• Weather on Other Worlds. II. Survey Results: Spots Are Ubiquitous on L and T Dwarfs
• Population Properties of Brown Dwarf Analogs to Exoplanets
• Confirmation of the Electron Cyclotron Maser Instability as the Dominant Source of Radio Emission from Very Low Mass Stars and Brown Dwarfs
• The Hawaii Infrared Parallax Program. II. Young Ultracool Field Dwarfs
• HST Spectral Mapping of L/T Transition Brown Dwarfs Reveals Cloud Thickness Variations
• Spitzer Infrared Spectrograph Observations of M, L, and T Dwarfs
• Strong Brightness Variations Signal Cloudy-to-Clear Transition of Brown Dwarfs
• Four nearby L dwarfs
• Flaring Up All Over -- Radio Activity in Rapidly-Rotating Late-Type M and L Dwarfs
• Magnetospherically driven optical and radio aurorae at the end of the stellar main sequence
• Vertical Atmospheric Structure in a Variable Brown Dwarf: Pressure-dependent Phase Shifts in Simultaneous Hubble Space Telescope-Spitzer Light Curves
• Retrieval of atmospheric properties of cloudy L dwarfs
• New study of the line profiles of sodium perturbed by H2
• The Slitless Spectroscopy Data Extraction Software aXe
• Brown Dwarf Photospheres are Patchy: A Hubble Space Telescope Near-infrared Spectroscopic Survey Finds Frequent Low-level Variability
• MIRACLES: atmospheric characterization of directly imaged planets and substellar companions at 4-5 $\mu$m. I. Photometric analysis of $\beta$ Pic b, HIP 65426 b, PZ Tel B and HD 206893 B
• Auroral radio emission from late L and T dwarfs: A new constraint on dynamo theory in the substellar regime
• BOSS Ultracool Dwarfs I: Colors and Magnetic Activity of M and L dwarfs
• Planets Around Low-Mass Stars (PALMS). III. A Young Dusty L Dwarf Companion at the Deuterium-Burning Limit
• Cloud busting: enstatite and quartz clouds in the atmosphere of 2M2224-0158
• A Physical Model-based Correction for Charge Traps in the Hubble Space Telescope's Wide Field Camera 3 Near-IR Detector and Applications to Transiting Exoplanets and Brown Dwarfs
• Let the Great World Spin: Revealing the Stormy, Turbulent Nature of Young Giant Exoplanet Analogs with the Spitzer Space Telescope
• Ultracool Dwarfs Observed with the Spitzer Infrared Spectrograph. II. Emergence and Sedimentation of Silicate Clouds in L Dwarfs, and Analysis of the Full M5--T9 Field Dwarf Spectroscopic Sample
• The Brown dwarf Atmosphere Monitoring (BAM) Project I: The largest near-IR monitoring survey of L- & T-dwarfs
• High-Cadence, High-Contrast Imaging for Exoplanet Mapping: Observations of the HR 8799 Planets with VLT/SPHERE Satellite Spot-Corrected Relative Photometry
• An independent analysis of the brown dwarf atmosphere monitoring (BAM) data: large-amplitude variability is rare outside the L/T transition
• Spectral Variability from the Patchy Atmospheres of T and Y Dwarfs
• Kepler Monitoring of an L Dwarf I. The Photometric Period and White Light Flares
• Starspot distributions on fully convective M dwarfs: implications for radial velocity planet searches
• Thermo-compositional diabatic convection in the atmospheres of brown dwarfs and in Earth's atmosphere and oceans
• Spitzer Variability Properties of Low-Gravity L Dwarfs
• Patchy Forsterite Clouds in the Atmospheres of Two Highly Variable Exoplanet Analogs
• 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
• Periodic Radio Emission from the M7 Dwarf 2MASS J13142039+1320011: Implications for the Magnetic Field Topology
• Variability of the Lowest Mass Objects in the AB Doradus Moving Group
• Strong Near-Infrared Spectral Variability of the Young Cloudy L Dwarf Companion VHS J1256-1257 b
• Atmospheric retrievals with petitRADTRANS
• Periodic Optical Variability of Radio Detected Ultracool Dwarfs
• Improving transit characterisation with Gaussian process modelling of stellar variability
• Maps of Evolving Cloud Structures in Luhman 16AB from HST Time-Resolved Spectroscopy
• Variability and periodicity of field M dwarfs revealed by multichannel monitoring
• Peering into the Young Planetary System AB Pic. Atmosphere, Orbit, Obliquity & Second Planetary Candidate
• The JWST Weather Report from the Nearest Brown Dwarfs I: multi-period JWST NIRSpec + MIRI monitoring of the benchmark binary brown dwarf WISE 1049AB
• 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
• Molecules as magnetic probes of starspots
• Rotational Modulation of M/L Dwarfs due to Magnetic Spots
• A Very High Proper Motion Star and the First L dwarf in the Kepler Field
• Contemporaneous Imaging Comparisons of the Spotted Giant $\sigma$ Geminorum Using Interferometric, Spectroscopic, and Photometric Data
• Cloud Atlas: Rotational Modulations in the L/T Transition Brown Dwarf Companion HN Peg B
• 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
• Methane Emission From a Cool Brown Dwarf
• 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
• Rotational spectral modulation of cloudless atmospheres for L/T Brown Dwarfs and Extrasolar Giant Planets
• $K2$ Ultracool Dwarfs Survey. VI. White light superflares observed on an L5 dwarf and flare rates of L dwarfs
• EXTraS discovery of an X-ray superflare from an L dwarf
• Kepler Monitoring of an L Dwarf II. Clouds with Multiyear Lifetimes
• Cloud Atlas: High-precision HST/WFC3/IR Time-Resolved Observations of Directly-Imaged Exoplanet HD106906b
• Limits on the Auroral Generation of H${}_3^{+}$ in Brown Dwarf and Extrasolar Giant Planet Atmospheres with Keck/NIRSPEC
• Cloud Atlas: Unraveling the vertical cloud structure with the time-series spectrophotometry of an unusually red brown dwarf
• On the Correlation between L Dwarf Optical and Infrared Variability and Radio Aurorae
• The JWST Weather Report: retrieving temperature variations, auroral heating, and static cloud coverage on SIMP-0136
• Detection of photometric variability in the very low-mass binary VHS J1256-1257AB using TESS and Spitzer
• Helium abundance in giant planets and the local interstellar medium
• Estimates of Densities and Filling Factors from a Cooling Time Analysis of Solar Microflares Observed with RHESSI
• Simulations of Electron Beam Interactions in Brown Dwarf Atmospheres