Electronic Telegram No. 1450 Central Bureau for Astronomical Telegrams INTERNATIONAL ASTRONOMICAL UNION M.S. 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A. IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions) CBAT@CFA.HARVARD.EDU (science) URL http://www.cfa.harvard.edu/iau/cbat.html 2008 BT_18 L. A. M. Benner, Jet Propulsion Laboratory (JPL), California Institute of Technology (CIT); M. C. Nolan and E. S. Howell, Arecibo Observatory, National Astronomy and Ionosphere Center; C. Magri, University of Maine at Farmington; J. D. Giorgini, S. J. Ostro, and M. Brozovic, JPL/CIT; M. W. Busch, CIT; J. L. Margot and P. A. Taylor, Cornell University; M. K. Shepard, Bloomsburg University; L. M. Carter, Smithsonian Institution; and T. M. Becker, Lehigh University, report that Arecibo (2380-MHz, 12.6-cm) and Goldstone (8560-MHz, 3.5-cm) radar observations during July 6, 7, and 11 reveal that minor planet 2008 BT_18 (cf. MPECs 2008-C03, 2008-H06; MPO 140193) is a binary system. Preliminary estimates for the component diameters are about 0.6 km and > 200 m. The maximum distance between the components on July 11 is at least 1.5 km. NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2008 CBAT 2008 July 29 (CBET 1450) Daniel W. E. Green