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Published May 2012 | Published + Accepted Version
Journal Article Open

Rotational Velocities of Individual Components in Very Low Mass Binaries


We present rotational velocities for individual components of 11 very low mass (VLM) binaries with spectral types between M7 and L7.5. These results are based on observations taken with the near-infrared spectrograph, NIRSPEC, and the Keck II laser guide star adaptive optics system. We find that the observed sources tend to be rapid rotators (v sin i > 10 km s^(–1)), consistent with previous seeing-limited measurements of VLM objects. The two sources with the largest v sin i, LP 349–25B and HD 130948C, are rotating at ~30% of their break-up speed, and are among the most rapidly rotating VLM objects known. Furthermore, five binary systems, all with orbital semimajor axes ≾3.5 AU, have component v sin i values that differ by greater than 3σ. To bring the binary components with discrepant rotational velocities into agreement would require the rotational axes to be inclined with respect to each other, and that at least one component is inclined with respect to the orbital plane. Alternatively, each component could be rotating at a different rate, even though they have similar spectral types. Both differing rotational velocities and inclinations have implications for binary star formation and evolution. We also investigate possible dynamical evolution in the triple system HD 130948A–BC. The close binary brown dwarfs B and C have significantly different v sin i values. We demonstrate that components B and C could have been torqued into misalignment by the primary star, A, via orbital precession. Such a scenario can also be applied to another triple system in our sample, GJ 569A–Bab. Interactions such as these may play an important role in the dynamical evolution of VLM binaries. Finally, we note that two of the binaries with large differences in component v sin i, LP 349–25AB and 2MASS 0746+20AB, are also known radio sources.

Additional Information

© 2012 American Astronomical Society. Received 2011 July 8; accepted 2012 February 24; published 2012 April 17. The authors thank the observing assistants Joel Aycock, Heather Hershley, Carolyn Parker, Gary Puniwai, Chuck Sorenson, Terry Stickel, and Cynthia Wilburn, and support astronomers Randy Campbell, Al Conrad, Marc Kassis, Jim Lyke, and Hien Tran for their help in obtaining the observations. We thank John Bailey for helpful advice regarding the analysis. We also thank an anonymous referee for helpful suggestions for the improvement of this document. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under the Contract DE-AC52-07NA27344. Support for this work was provided by the NASA Origins Program (NNX1 OAH39G) and the NSF Science & Technology Center for AO, managed by UCSC (AST-9876783). Some of the spectral analysis tools used in this study were developed in part by funding provided by the NSF/AAG Grant #0908018. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. The W.M. Keck Observatory is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. The authors also wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

Attached Files

Published - Konopacky2012p18208Astrophys_J.pdf

Accepted Version - 1202.5555.pdf


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