L-dwarf variability: Magnetic star spots or non-uniform clouds?
Abstract
The recent discovery of photometric variations in L dwarfs has opened a discussion on the cause of the variations. We argue against the existence of magnetic spots in these atmospheres and favor the idea that non-uniform condensate coverage (i.e. clouds) is responsible for the variations. The magnetic Reynolds number (Rm) in the atmosphere of L dwarfs, which describes how well the gas couples with the magnetic field, is too small (<<1) to support the formation of magnetic spots. In constrast silicate and iron clouds form in the photospheres of L dwarfs. Inhomogeneities in such cloud decks can plausibly produce the observed photometric variations. Further evidence in support of clouds is the tendency for variable L dwarfs to be bluer in J-Ks than the average L dwarf of a given spectral type. This color effect is expected if clear holes appear in an otherwise uniform cloud layer.
Cite
@article{arxiv.astro-ph/0106062,
title = {L-dwarf variability: Magnetic star spots or non-uniform clouds?},
author = {Christopher R. Gelino and Mark S. Marley and Jon A. Holtzman and Andrew S. Ackerman and Katharina Lodders},
journal= {arXiv preprint arXiv:astro-ph/0106062},
year = {2007}
}
Comments
submitted to ApJL, 13 pages, 2 figures