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C.A.L. Bailer-Jones (Max-Planck-Institut fuer Astronomie)
Recent work has shown that photometric variability is relatively common in late M and L dwarfs. In several cases, this variability appears to be nonperiodic, suggesting that the putative surface features modulating the light curve are evolving on a time scale comparable to the rotation period. I shall review this work, plus more recent attempts to identify the nature of these surface features, in particular to distinguish between magnetically induced star spots and dust-related clouds. Dust is known to form in the atmospheres of ultra cool dwarfs (UCDs), and the relative efficiencies of dust precipitation and convective recycling is a factor in determining the distribution of this dust in the atmosphere. Given that UCDs are probably fully convective and are generally rapid rotators (with periods of just a few hours), turbulence-driven surface inhomogeneities are a possible source of photometric variability. However, the detection of X-ray emission and radio and H\alpha flaring indicates that magnetic fields may yet have a role to play in this.
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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.