Electronic Telegram No. 1143 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 (16635) 1993 QO D. Pray, Carbuncle Hill Observatory, Greene, RI; P. Pravec, P. Kusnirak, and K. Hornoch, Ondrejov Observatory; Yu. Krugly and V. Chiorny, Institute of Astronomy, Kharkiv National University, National Academy of Science of Ukraine; M. Husarik and M. Pikler, Skalnate Pleso Observatory; J. Vilagi, S. Gajdos, and A. Galad, Modra Observatory; W. Cooney, J. Gross, and D. Terrell, Sonoita Research Observatory, Sonoita, AZ; N. Gaftonyuk, Simeiz Observatory; R. Stephens, Goat Mountain Astronomical Research Station, Yucca Valley, CA; R. Durkee, Minneapolis, MN; F. Marchis and M. Baek, SETI Institute; B. Macomber, University of California at Berkeley; V. Reddy, Department of Earth System Science and Policy, University of North Dakota, Grand Forks; F. Colas and J. Lecacheux, IMCCE and Pic du Midi Observatory; and J. Ries, McDonald Observatory, report that photometric observations obtained during Sept. 2- Nov. 9 reveal that minor planet (16635) is a binary system with an orbital period of 32.25 +/- 0.03 hr. Additive rotation lightcurves of system's components have periods 2.2083 +/- 0.0002 and 7.622 +/- 0.002 hr and amplitudes 0.17 and 0.05 mag, respectively. Mutual events indicate a lower limit on the secondary-to-primary mean-diameter ratio of 0.27. Calibrated data give an estimated mean absolute magnitude H_R = 14.0 +/- 0.3, assuming G = 0.15 +/- 0.2. NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2007 CBAT 2007 November 19 (CBET 1143) Daniel W. E. Green