Accepted for publication in The Astrophysical Journal Preprint typeset using L A T E X style emulateapj v. 5/2/11 CHARACTERIZATION OF THE BENCHMARK BINARY NLTT 33370 †* Joshua E. Schlieder 1,2 , Micka¨ el Bonnefoy 1,3 , T. M. Herbst 1 , S´ ebastien L´ epine 4,5 , Edo Berger 6 , Thomas Henning 1 , Andrew Skemer 7 , Ga¨ el Chauvin 3 , Emily Rice 2,4,8 , Beth Biller 1,9 , Julien H. V. Girard 10 , Anne-Marie Lagrange 3 , Philip Hinz 7 , Denis Defr` ere 7 , Carolina Bergfors 1,11 , Wolfgang Brandner 1 , Sylvestre Lacour 12 , Michael Skrutskie 13 , Jarron Leisenring 7,14 Accepted for publication in The Astrophysical Journal ABSTRACT We report the confirmation of the binary nature of the nearby, very low-mass system NLTT 33370 with adaptive optics imaging and present resolved near-infrared photometry and integrated light optical and near-infrared spectroscopy to characterize the system. VLT-NaCo and LBTI-LMIRCam images show significant orbital motion between 2013 February and 2013 April. Optical spectra reveal weak, gravity sensitive alkali lines and strong lithium 6708 ˚ A absorption that indicate the system is younger than field age. VLT-SINFONI near-IR spectra also show weak, gravity sensitive features and spectral morphology that is consistent with other young, very low-mass dwarfs. We combine the constraints from all age diagnostics to estimate a system age of ∼30-200 Myr. The 1.2-4.7 µm spectral energy distribution of the components point toward T eff = 3200 ± 500 K and T eff = 3100 ± 500 K for NLTT 33370 A and B, respectively. The observed spectra, derived temperatures, and estimated age combine to constrain the component spectral types to the range M6-M8. Evolutionary models predict masses of 113 ± 8 M Jup and 106 ± 7 M Jup from the estimated luminosities of the components. KPNO-Phoenix spectra allow us to estimate the systemic radial velocity of the binary. The Galactic kinematics of NLTT 33370AB are broadly consistent with other young stars in the Solar neighborhood. However, definitive membership in a young, kinematic group cannot be assigned at this time and further follow-up observations are necessary to fully constrain the system’s kinematics. The proximity, age, and late-spectral type of this binary make it very novel and an ideal target for rapid, complete orbit determination. The system is one of only a few model calibration benchmarks at young ages and very low-masses. Subject headings: stars: binaries — stars: late-type — stars: individual (NLTT 33370) schlieder@mpia-hd.mpg.de † Based on observations collected at the European Organi- zation for Astronomical Research in the Southern Hemisphere, Chile during program ID 090.C-0819 * The LBT is an international collaboration among institu- tions in the United States, Italy and Germany. LBT Corporation partners are: The University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; The Ohio State University, and The Research Cor- poration, on behalf of The University of Notre Dame, University of Minnesota and University of Virginia. 1 Max-Planck-Institut f¨ ur Astronomie, K¨onigstuhl 17, 69117, Heidelberg, Germany 2 Visiting Astronomer, Kitt Peak National Observatory, Na- tional Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA) under cooperative agreement with the National Science Founda- tion. 3 UJF-Grenoble 1 / CNRS-INSU, Institut de Plan´ etologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, Grenoble 38041, France 4 Department of Astrophysics, Division of Physical Sciences, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024, USA 5 Department of Physics and Astronomy, Georgia State Uni- versity, Atlanta, GA 30302-4106, USA 6 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA 7 Steward Observatory, Department of Astronomy, University of Arizona, 933 N. Cherry Ave, Tucson, AZ 85721, USA 8 Department of Engineering Science and Physics, College of Staten Island, City University of New York, 2800 Victory Blvd, Staten Island, NY 10314 9 Institute for Astronomy, University of Edinburgh, Blackford Hill View, Edinburgh EH9 3HJ, UK 10 European Southern Observatory, Casilla 19001, Santiago 19, Chile 11 Department of Physics and Astronomy, University College London, Gower Street, London, WC1E 6BT, UK 12 LESIA, Observatoire de Paris, CNRS, University Pierre et Marie Curie Paris 6 and University Denis Diderot Paris 7, 5 place Jules Janssen, 92195 Meudon, France 13 Department of Astronomy, University of Virginia, Char- lottesville, VA 22904, USA 14 Institute for Astronomy, ETH, Wolfgang-Pauli-Strasse 27, 8093 Zurich, Switzerland arXiv:1401.0947v1 [astro-ph.SR] 5 Jan 2014