Rotational Modulation of M/L Dwarfs due to Magnetic Spots

Abstract

We find periodic I-band variability in two ultracool dwarfs, TVLM 513-46546 and 2MASS J00361617+1821104, on either side of the M/L dwarf boundary. Both of these targets are short-period radio transients, with the detected I-band periods matching those found at radio wavelengths (P=1.96 hr for TVLM 513-46546, and P=3 hr for 2MASS J00361617+1821104). We attribute the detected I-band periodicities to the periods of rotation of the dwarfs, supported by radius estimates and measured $v$ sin $i$ values for the objects. Based on the detected period of rotation of TVLM 513-46546 (M9) in the I-band, along with confirmation of strong magnetic fields from recent radio observations, we argue for magnetically induced spots as the cause of this periodic variability. The I-band rotational modulation of L3.5 dwarf 2MASS J00361617+1821104 appeared to vary in amplitude with time. We conclude that the most likely cause of the I-band variability for this object is magnetic spots, possibly coupled with time-evolving features such as dust clouds.

11 pages, 2 figures, accepted for publication in ApJ Letters

References in corpus (3)

• The First Direct Measurements of Magnetic Fields on Very Low-Mass Stars
• Periodic Bursts of Coherent Radio Emission from an Ultracool Dwarf
• Rotational Modulation of the Radio Emission from the M9 Dwarf TVLM 513-46546: Broadband Coherent Emission at the Substellar Boundary?

Cited by in corpus (18)

• Confirmation of the Electron Cyclotron Maser Instability as the Dominant Source of Radio Emission from Very Low Mass Stars and Brown Dwarfs
• Strong Brightness Variations Signal Cloudy-to-Clear Transition of Brown Dwarfs
• Doppler Imaging of Exoplanets and Brown Dwarfs
• Simultaneous Multi-Wavelength Observations of Magnetic Activity in Ultracool Dwarfs. I. The Complex Behavior of the M8.5 Dwarf TVLM513-46546
• The Dawes Review 3: The Atmospheres of Extrasolar Planets and Brown Dwarfs
• A Mini-survey of Ultracool Dwarfs at 4.9 GHz
• The Second Arecibo Search for 5 GHz Radio Flares from Ultracool Dwarfs
• Steady and Transient Radio Emission from Ultracool Dwarfs
• Optical variability of the ultracool dwarf TVLM 513-46546: evidence for inhomogeneous dust clouds
• Timing Analysis of the Periodic Radio and Optical Brightness Variations of the Ultracool Dwarf, TVLM 513-46546
• Serendipitous discovery of radio flaring behaviour from a nearby M dwarf with MeerKAT
• The Deepest Constraints on Radio and X-ray Magnetic Activity in Ultracool Dwarfs from WISE J104915.57-531906.1
• Modelling the environment around five ultracool dwarfs via the radio domain
• Mapping the Skies of Ultracool Worlds: Detecting Storms and Spots with Extremely Large Telescopes
• Long-Term Evolution in Transit Duration of Extrasolar Planets from Magnetic Activity in their Parent Stars
• Long-term K${}_S$-band photometric monitoring of L dwarfs
• Optical Variability, Rotation Period and Inclination Angle of the M9.5 dwarf BRI 0021-0214
• Disentangling auroral, cloud and magnetic spot driven variability in three early L-dwarfs with HST/WFC3