(326732) 2003 HB_6

P. Pravec, K. Hornoch, H. Kucakova, P. Kusnirak, and P. Fatka, Ondrejov Observatory; E. Jehin and M. Ferrais, Liege University; M. Devogele, Arecibo Observatory and University of Central Florida; T. Kareta, University of Arizona; and N. Moskovitz, Lowell Observatory, report that photometric observations taken with a 0.65-m telescope at Ondrejov Observatory and a 0.6-m telescope at the La Silla station of the European Southern Observatory during Aug. 10-Sept. 15 reveal that the Amor-type minor planet (326732) is a binary system with an orbital period of 22.92 +/- 0.05 hr. The primary has a period of 3.4630 +/- 0.0008 hr and a lightcurve amplitude of 0.08 magnitude at solar phases 4-8 degrees, suggesting a nearly spheroidal shape. Mutual eclipse/occultation events that are 0.06 to 0.11 magnitude deep indicate a secondary-to-primary mean-diameter ratio of 0.23 +/- 0.02. The secondary appears synchronous and has a light-curve amplitude (in the combined primary- plus-secondary light curve) of 0.02 mag, suggesting a moderately elongated shape with an equatorial-axis ratio of 1.4 +/- 0.2. The system's mean absolute magnitude is H = 17.42 +/- 0.04, assuming a phase-relation slope parameter G = 0.24 +/- 0.11. The color index in the Johnson-Cousins photometric system is (V - R) = 0.429 +/- 0.010. Spectroscopic observations taken with the DeVeny spectrograph at the 4.3-m Lowell Discovery Telescope in the wavelength range 0.38-1.0 micron suggest it to be of L-type in the Bus-DeMeo taxonomic system, but other classifications are not excluded. These observations were taken in the framework of their NEOROCKS and MANOS projects. Follow-up observations are encouraged.