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Published October 20, 2007 | Published + Submitted
Journal Article Open

Rotational Modulation of M/L Dwarfs due to Magnetic Spots


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 the 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.

Additional Information

© 2007 American Astronomical Society. Received 2007 June 26; accepted 2007 September 5; published 2007 October 2. This work is supported by Science Foundation Ireland under its Research Frontiers Programme, the Higher Education Authority's Programme for Research in Third Level Institutions, and the Irish Research Council for Science, Engineering, and Technology. Armagh Observatory is grant-aided by the Northern Ireland Department of Culture, Arts, and Leisure. We also thank Hugh Harris and our referee for their suggestions, which have greatly improved the manuscript.

Attached Files

Published - 1538-4357_668_2_L163.pdf

Submitted - 0709.1045v1.pdf


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