Bouy, H. and Martín, E. L. and Brandner, W. and Forveille, T. and Delfosse, X. and Huélamo, N. and Basri, G. and Girard, J. and Zapatero Osorio, M.-R. and Stumpf, M. and Ghez, A. and Valdivielso, L. and Marchis, F. and Burgasser, A. J. and Cruz, K. (2008) Follow-up observations of binary ultra-cool dwarfs. Astronomy and astrophysics, 481 . pp. 757-767. ISSN 0004-6361 http://resolver.caltech.edu/CaltechAUTHORS:20090407-141128964
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Context. Astrometric observations of resolved binaries provide estimates of orbital periods and will eventually lead to measurement of dynamical masses. Only a few very low mass star and brown dwarf masses have been measured to date, and the mass-luminosity relation still needs to be calibrated. Aims. We have monitored 14 very low mass multiple systems for several years to confirm their multiplicity and, for those with a short period, derive accurate orbital parameters and dynamical mass estimates. Methods. We have used high spatial resolution images obtained at the Paranal, Lick and HST observatories to obtain astrometric and photometric measurements of the multiple systems at several epochs. The targets have periods ranging from 5 to 200 years, and spectral types in the range M7.5–T5.5. Results. All of our 14 multiple systems are confirmed as common proper motion pairs. One system (2MASSW J0920122+351742) is not resolved in our new images, probably because the discovery images were taken near maximum elongation. Six systems have periods short enough to allow dynamical mass measurements within the next 15 to 20 years.We estimate that only 8% of the ultracool dwarfs in the solar neighborhood are binaries with separations large enough to be resolved, and yet periods short enough to derive astrometric orbital fits over a reasonable time frame with current instrumentation. A survey that doubles the number of ultracool dwarfs observed with high angular resolution is called for to discover enough binaries for a first attempt to derive the mass-luminosity relationship for very low-mass stars and brown dwarfs.
|Additional Information:||© ESO 2008. Received 5 October 2007 / Accepted 31 January 2008. H. Bouy acknowledges the funding from the European Commission’s Sixth Framework Program as a Marie Curie Outgoing International Fellow (MOIF-CT-2005-8389). We acknowledge the kind and efficient support of Tricia Royle at STScI, Elinor Gates and Bernie Walp at Lick Observatory, and Lowell Tacconi-Garman at ESO and are grateful for their precious help. We also thank our anonymous referee for helping us improving this article. W. Brandner acknowledges support by the Deutsches Zentrum für Luft- und Raumfahrt (DLR), Förderkennzeichen 50 OR 0401. This work is based on observations collected at the European Southern Observatory (Paranal, Chile), programs 70.D-0773, 077.C-0062, 71.C-0327, P. I. Bouy, at the Lick Observatory, with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute (STScI), programs GO-9157, GO- 9345,GO-9499 and GO-9968, GO-10559 and GO-9451. The STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. 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.|
|Subject Keywords:||stars: low-mass, brown dwarfs – binaries: visual – techniques: high angular resolution|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||25 Jun 2009 18:30|
|Last Modified:||26 Dec 2012 10:56|
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