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Published December 20, 2013 | Published + Submitted
Journal Article Open

Periodic Optical Variability of Radio-detected Ultracool Dwarfs


A fraction of very low mass stars and brown dwarfs are known to be radio active, in some cases producing periodic pulses. Extensive studies of two such objects have also revealed optical periodic variability, and the nature of this variability remains unclear. Here, we report on multi-epoch optical photometric monitoring of six radio-detected dwarfs, spanning the ~M8-L3.5 spectral range, conducted to investigate the ubiquity of periodic optical variability in radio-detected ultracool dwarfs. This survey is the most sensitive ground-based study carried out to date in search of periodic optical variability from late-type dwarfs, where we obtained 250 hr of monitoring, delivering photometric precision as low as ~0.15%. Five of the six targets exhibit clear periodicity, in all cases likely associated with the rotation period of the dwarf, with a marginal detection found for the sixth. Our data points to a likely association between radio and optical periodic variability in late-M/early-L dwarfs, although the underlying physical cause of this correlation remains unclear. In one case, we have multiple epochs of monitoring of the archetype of pulsing radio dwarfs, the M9 TVLM 513–46546, spanning a period of 5 yr, which is sufficiently stable in phase to allow us to establish a period of 1.95958 ± 0.00005 hr. This phase stability may be associated with a large-scale stable magnetic field, further strengthening the correlation between radio activity and periodic optical variability. Finally, we find a tentative spin-orbit alignment of one component of the very low mass binary, LP 349–25.

Additional Information

© 2013 American Astronomical Society. Received 2012 June 23; accepted 2013 September 27; published 2013 November 27. This work was largely carried out under the National University of Ireland Traveling Studentship in the Sciences (Physics). L.K.H. gratefully acknowledges the support of the Science Foundation Ireland (Grant Number 07/RFP/PHYF553). We thank the VATT team for their help and guidance, especially Dave Harvey, Michael Franz, and Ken Duffek. L.K.H. personally thanks Dr. Mark Lang for his constant assistance, in addition to the staff of the NRAO who provided significant support when L.K.H. was conducting some of his work during his appointment as an NRAO graduate intern. We extend our thanks to Dr. Stuart Littlefair for his many helpful comments on this work. Finally, we thank the editor, Dr. Steven Kawaler, in addition to the referee for their careful reading of our work and for their helpful input on how to improve this manuscript.

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Published - 0004-637X_779_2_101.pdf

Submitted - 1310.1367v1.pdf


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