Radial Velocity Variability of Field Brown Dwarfs

Creators: Prato, L.; Mace, G. N.; Rice, E. L.; McLean, I. S.; Kirkpatrick, J. Davy; Burgasser, A. J.; Kim, Sungsoo S.

Abstract

We present paper six of the NIRSPEC Brown Dwarf Spectroscopic Survey, an analysis of multi-epoch, high-resolution (R ~ 20,000) spectra of 25 field dwarf systems (3 late-type M dwarfs, 16 L dwarfs, and 6 T dwarfs) taken with the NIRSPEC infrared spectrograph at the W. M. Keck Observatory. With a radial velocity (RV) precision of ~2 km s^−1, we are sensitive to brown dwarf companions in orbits with periods of a few years or less given a mass ratio of 0.5 or greater. We do not detect any spectroscopic binary brown dwarfs in the sample. Given our target properties, and the frequency and cadence of observations, we use a Monte Carlo simulation to determine the detection probability of our sample. Even with a null detection result, our 1σ upper limit for very low mass binary frequency is 18%. Our targets included seven known, wide brown dwarf binary systems. No significant RV variability was measured in our multi-epoch observations of these systems, even for those pairs for which our data spanned a significant fraction of the orbital period. Specialized techniques are required to reach the high precisions sensitive to motion in orbits of very low-mass systems. For eight objects, including six T dwarfs, we present the first published high-resolution spectra, many with high signal to noise, that will provide valuable comparison data for models of brown dwarf atmospheres.

Additional Information

© 2015 The American Astronomical Society. Received 2015 February 11; accepted 2015 June 6; published 2015 July 14. We thank the Keck Observatory OAs and SAs and B. Schaefer, probably all of whom helped with these runs and observations during the 11 year period over which the data were gathered, for their exceptional support. We are grateful to Q. Konopacky and M. McGovern for assistance with some of the later observing runs. L.P. thanks O. Franz and L. Wasserman for helpful discussions on orbital dynamics. We are grateful to the anonymous referee for comments that improved this manuscript. Partial support to L.P. for this work was provided by NSF grant AST 04-44017. This research has benefited from the M, L, T, and Y dwarf compendium housed at DwarfArchives.org. This work made use of the SIMBAD reference database, the NASA Astrophysics Data System, and the data products from the 2MASS, 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. Data presented herein were obtained at the W. M. Keck Observatory, which 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 recognize and acknowledge the significant cultural role that the summit of Mauna Kea plays within the indigenous Hawaiian community. We are grateful for the opportunity to conduct observations from this special mountain.

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