D. Pray, Sugarloaf Mountain Observatory, South Deerfield, MA, U.S.A.; J. Oey, Blue Mountains Observatory, Leura, NSW, Australia; P. Pravec, H. Kucakova, and K. Hornoch, Ondrejov Observatory; V. Benishek, Belgrade Astronomical Observatory; and A. Marchini, R. Papini, and F. Salvaggio, Dipartimento di Scienze Fisiche, Della Terra e Dell’Ambiente, University of Siena, report that photometric observations obtained with a 0.50-m telescope at the Sugarloaf Mountain Observatory, a 0.35m telescope at the Blue Mountains Observatory, a 0.65-m telescope at the Ondrejov Observatory, a 0.35-m telescope at the Sopot Observatory in Serbia, and a 0.30-m telescope at the Astronomical Observatory of the University of Siena during July 16-Sept. 25 reveal that minor planet (23621), whose orbit crosses that of Mars, is a binary system with an orbital period of 20.60 ± 0.03 hr. The primary shows a period of 2.6649 h ± 0.0005 hr and has a lightcurve amplitude of 0.07 mag at solar phases 1-4 degrees, suggesting a nearly spheroidal shape. Mutual eclipse/occultation events that are 0.04- to 0.12-magnitude deep indicate a lower limit on the secondary-to-primary mean-diameter ratio of 0.27.
2017 October 4 (CBET 4436) Daniel W. E. Green