Binary asteroid discovery IAU announcement


(100015) 1989 SR7
V. Benishek, Belgrade Astronomical Observatory; P. Pravec, H. Kucakova,
K. Hornoch, and P. Kusnirak, Ondrejov Observatory; J. Oey, Blue Mountains
Observatory, Leura, NSW, Australia; R. Groom, Darling Range Observatory,
Perth, Western Australia; A. Aznar, Astronomia Para Todos Observatories Group,
Spain; and A. Sota, Observatorio de Sierra Nevada, Instituto de Astrofisica de
Andalucia-CSIC, report that photometric observations taken with a 0.35-m
telescope at the Sopot Observatory in Serbia, a 0.65-m telescope at the
Ondrejov Observatory, a 0.35-m telescope at the Blue Mountains Observatory, a
0.30-m telescope at the Darling Range Observatory, and a 0.90-m telescope at
the Sierra Nevada Observatory during Sept. 9-Oct. 12 reveal that minor planet
(100015) is a binary system with an orbital period of 20.65 ± 0.01 hr. The
primary shows a period of 2.4172 ± 0.0002 hr and has a lightcurve amplitude
of 0.05 mag at solar phases 7-22 degrees, suggesting a nearly spheroidal
shape. Mutual eclipse/occultation events that are 0.13 to 0.21 magnitude deep
indicate a secondary-to-primary mean-diameter ratio of 0.35 ± 0.02. The
mean absolute R magnitude in the Cousins system is H_R = 15.55 ± 0.11,
assuming the phase-relation slope parameter G = 0.24 ± 0.11.

2018 October 23,  Daniel W. E. Green