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 sin 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.
Keywords
Cite
@article{arxiv.0709.1045,
title = {Rotational Modulation of M/L Dwarfs due to Magnetic Spots},
author = {C. Lane and G. Hallinan and R. T. Zavala and R. F. Butler and R. P. Boyle and S. Bourke and A. Antonova and J. G. Doyle and F. J. Vrba and A. Golden},
journal= {arXiv preprint arXiv:0709.1045},
year = {2009}
}
Comments
11 pages, 2 figures, accepted for publication in ApJ Letters