Kepler Monitoring of an L Dwarf I. The Photometric Period and White Light Flares

Abstract

We report on the results of fifteen months of monitoring the nearby field L1 dwarf WISEP J190648.47+401106.8 (W1906+40) with the Kepler mission. Supporting observations with the Karl G. Jansky Very Large Array and Gemini North telescope reveal that the L dwarf is magnetically active, with quiescent radio and variable H$\alpha$ emission. A preliminary trigonometric parallax shows that W1906+40 is at a distance of $16.35_{-0.34}^{+0.36}$ pc, and all observations are consistent with W1906+40 being an old disk star just above the hydrogen-burning limit. The star shows photometric variability with a period of 8.9 hours and an amplitude of 1.5%, with a consistent phase throughout the year. We infer a radius of $0.92\pm 0.07R_J$ and $\sin i>0.57$ from the observed period, luminosity ($10^{-3.67\pm 0.03}{L}_{\odot }$), effective temperature ($2300\pm 75$K), and $v\sin i$ ($11.2\pm 2.2$ km/s). The light curve may be modeled with a single large, high latitude dark spot. Unlike many L-type brown dwarfs, there is no evidence of other variations at the $\gtrsim 2$ level, either non-periodic or transient periodic, that mask the underlying rotation period. We suggest that the long-lived surface features may be due to starspots, but the possibility of cloud variations cannot be ruled out without further multi-wavelength observations. During the Gemini spectroscopy, we observed the most powerful flare ever seen on an L dwarf, with an estimated energy of $\sim 1.6\times 10^{32}$ ergs in white light emission. Using the Kepler data, we identify similar flares and estimate that white light flares with optical/ultraviolet energies of $10^{31}$ ergs or more occur on W1906+40 as often as 1-2 times per month.

accepted to ApJ

References in corpus (16)

• Young L Dwarfs Identified in the Field: A Preliminary Low-Gravity, Optical Spectral Sequence from L0 to L5
• Chromospheric Activity, Rotation, and Rotational Braking in M and L Dwarfs
• Confirmation of the Electron Cyclotron Maser Instability as the Dominant Source of Radio Emission from Very Low Mass Stars and Brown Dwarfs
• Radio Observations of a Large Sample of Late-M, L, and T Dwarfs: The Distribution of Magentic Field Strengths
• Activity and Kinematics of Ultracool Dwarfs Including An Amazing Flare Observation
• Rotational Modulation of the Radio Emission from the M9 Dwarf TVLM 513-46546: Broadband Coherent Emission at the Substellar Boundary?
• A White Light Megaflare on the dM4.5e Star YZ CMi
• Vertical Atmospheric Structure in a Variable Brown Dwarf: Pressure-dependent Phase Shifts in Simultaneous Hubble Space Telescope-Spitzer Light Curves
• Radiative Hydrodynamic Models of Optical and Ultraviolet Emission from M Dwarf Flares
• Simultaneous Multi-Wavelength Observations of Magnetic Activity in Ultracool Dwarfs. II. Mixed Trends in VB10 and LSR1835+32 and the Possible Role of Rotation
• Multiwavelength observations of a giant flare on CN Leonis I. The chromosphere as seen in the optical spectra
• Simultaneous Multi-Wavelength Observations of Magnetic Activity in Ultracool Dwarfs. I. The Complex Behavior of the M8.5 Dwarf TVLM513-46546
• Simultaneous optical and X-ray observations of a giant flare on the ultracool dwarf LP412-31
• A Spectroscopic Binary at the M/L Transition
• Rotational Modulation of M/L Dwarfs due to Magnetic Spots
• Quasi-Quiescent Radio Emission from the First Radio-Emitting T Dwarf

Cited by in corpus (52)

• Kepler Flares I. Active and Inactive M dwarfs
• Water loss from Earth-sized planets in the habitable zones of ultracool dwarfs: Implications for the planets of TRAPPIST-1
• Do Kepler superflare stars really include slowly-rotating Sun-like stars ? - Results using APO 3.5m telescope spectroscopic observations and Gaia-DR2 data -
• Photometry and Proper Motions of M, L, and T Dwarfs from the Pan-STARRS1 3$\pi$ Survey
• A Volume-Limited Sample of Ultracool Dwarfs. I. Construction, Space Density, and a Gap in the L/T Transition
• The Viewing Geometry of Brown Dwarfs Influences Their Observed Colours and Variability Properties
• Doppler Imaging of Exoplanets and Brown Dwarfs
• The Evolution of Flare Activity with Stellar Age
• A Panchromatic View of Brown Dwarf Aurorae
• K2 Ultracool Dwarfs Survey. III. White Light Flares are Ubiquitous in M6-L0 Dwarfs
• Spectral Variability from the Patchy Atmospheres of T and Y Dwarfs
• The Hawaii Infrared Parallax Program. IV. A Comprehensive Parallax Survey of L0-T8 dwarfs with UKIRT
• Hydrogen Balmer Line Broadening in Solar and Stellar Flares
• Flares in Open Clusters with K2. II. Pleiades, Hyades, Praesepe, Ruprecht 147, and M67
• Kepler Flares III: Stellar Activity on GJ 1245 A and B
• Variability of the Lowest Mass Objects in the AB Doradus Moving Group
• High-resolution spectroscopy of flares and CMES on AD Leo*
• The largest M dwarfs flares from ASAS-SN
• Astrometric planet search around southern ultracool dwarfs I: First results, including parallaxes of 20 M8-L2 dwarfs
• ASASSN-16ae: A Powerful White-Light Flare on an Early-L Dwarf
• The Rotation Period and Magnetic Field of the T Dwarf 2MASSI J1047539+212423 Measured From Periodic Radio Bursts
• K2 Ultracool Dwarfs Survey II: The White Light Flare Rate of Young Brown Dwarfs
• K2 Ultracool Dwarfs Survey. V. High superflare rates on rapidly rotating late-M dwarfs
• A Study of Flares in the Ultra-Cool Regime from SPECULOOS-South
• K2 Ultracool Dwarfs Survey I: Photometry of an L Dwarf Superflare
• $K2$ Ultracool Dwarfs Survey. VI. White light superflares observed on an L5 dwarf and flare rates of L dwarfs
• The CARMENES search for exoplanets around M dwarfs: Wing asymmetries of H$\alpha$, Na I D, and He I lines
• Weather on Other Worlds. IV. H$\alpha$ emission and photometric variability are not correlated in L0$-$T8 dwarfs
• Detection of a giant white-light flare on an L2.5 dwarf with the Next Generation Transit Survey
• Kepler Monitoring of an L Dwarf II. Clouds with Multiyear Lifetimes
• WISEP J060738.65+242953.4: A Nearby. Pole-On L8 Brown Dwarf with Radio Emission
• Optical Spectra of Ultracool Dwarfs with the Southern African Large Telescope
• High resolution near-infrared spectroscopy of a flare around the ultracool dwarf vB 10
• A $\Delta R\sim 9.5$ mag Super Flare of An Ultracool Star Detected by $\text{SVOM/GWAC}$ System
• Flaring-associated Complex Dynamics in Two M-dwarfs Revealed by Fast, Time-resolved Spectroscopy
• Lower-than-expected flare temperatures for TRAPPIST-1
• Radio Emission from Binary Ultracool Dwarf Systems
• The Occurrence Rate of Quiescent Radio Emission for Ultracool Dwarfs using a Generalized Semi-Analytical Bayesian Framework
• Spectral Variability of Two Rapidly Rotating Brown Dwarfs: 2MASS J08354256-0819237 and 2MASS J18212815+1414010
• A first eROSITA view of ultracool dwarfs
• The photometric periods of rapidly rotating field ultra-cool dwarfs
• Radio Emission from Ultra-Cool Dwarfs
• The M4.5V flare star AF Psc as seen in K2 engineering data
• The Potential of Detecting Radio-flaring Ultracool Dwarfs at L band in the FAST Drift-scan Survey
• 2MASS J10274572+0629104: The very short period young M6 Dwarf Binary System identified in K2 data
• A huge-amplitude white-light superflare on a L0 brown dwarf discovered by GWAC survey
• Searching for I band variability in stars in the M/L spectral transition region
• The corona of a fully convective star with a near-polar flare
• Spectral analysis of two directly imaged benchmark L dwarf companions at the stellar-substellar boundary
• Disentangling auroral, cloud and magnetic spot driven variability in three early L-dwarfs with HST/WFC3
• Using Old and New Approaches: Determining Physical Properties of Brown Dwarfs with Empirical Relations and Machine Learning Models
• Dynamic Photometric Variability in Three Young Brown Dwarfs in Taurus: Detection of Optical Flares with TESS data