Electronic Telegram No. 5255 Central Bureau for Astronomical Telegrams Mailing address: Hoffman Lab 209; Harvard University; 20 Oxford St.; Cambridge, MA 02138; U.S.A. e-mail: cbatiau@eps.harvard.edu (alternate cbat@iau.org) URL http://www.cbat.eps.harvard.edu/index.html Prepared using the Tamkin Foundation Computer Network (5781) BARKHATOVA V. Benishek, Belgrade Astronomical Observatory; P. Pravec, Ondrejov Observatory; and R. Durkee, Shed of Science South Observatory, Pontotoc, TX, U.S.A., report that photometric observations taken with a 0.35-m telescope at the Sopot Observatory in Serbia and a 0.50-m telescope at the Shed of Science South Observatory during Mar. 14-Apr. 12 reveal that minor planet (5781) is a binary system with an orbital period of 36.04 +/- 0.05 hr. The primary shows a period of 2.8161 +/- 0.0001 hr and has a lightcurve amplitude of 0.12 magnitude at solar phases 5-19 degrees, suggesting a nearly spheroidal shape. Mutual eclipse/occultation events that are 0.07 to 0.14 magnitude deep indicate a lower limit on the secondary-to-primary mean-diameter ratio of 0.26. NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2023 CBAT 2023 May 11 (CBET 5255) Daniel W. E. Green