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.

arXiv comment11 pages, 2 figures, accepted for publication in ApJ Letters

References in corpus (13)

• The Limiting Effects of Dust in Brown Dwarf Model Atmospheres
• Astrometry and Photometry for Cool Dwarfs and Brown Dwarfs
• Sixty-seven Additional L Dwarfs Discovered by the Two Micron All Sky Survey (2MASS)
• The First Direct Measurements of Magnetic Fields on Very Low-Mass Stars
• Activity in Very Cool Stars: Magnetic Dissipation in late-M and L Dwarf Atmospheres
• Periodic Bursts of Coherent Radio Emission from an Ultracool Dwarf
• Variability in ultra cool dwarfs: evidence for the evolution of surface features
• L-dwarf variability: I-band observations
• Rotational Modulation of the Radio Emission from the M9 Dwarf TVLM 513-46546: Broadband Coherent Emission at the Substellar Boundary?
• Spectroscopic rotational velocities of brown dwarfs
• The Magnetic Properties of an L Dwarf Derived from Simultaneous Radio, X-ray, and H-alpha Observations
• Photometric Variability in the Ultracool Dwarf BRI 0021-0214: Possible Evidence for Dust Clouds
• Variability and periodicity of field M dwarfs revealed by multichannel monitoring

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