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G. J. Consolmagno (Vatican Observatory), S. C. Tegler (N. Arizona U.), T. Rettig (U. Notre Dame), W. Romanishin (U. Oklahoma)
The outer Solar System object 1999 TD10 is unusual in that it has a perihelion distance similar to Centaurs, 12 AU, but a semi-major axis similar to scattered disk objects, 190 AU. We obtained CCD images of 1999 TD10 using the University of Arizona 2.3-m telescope on Kitt Peak, Arizona on 1999 November 8 and 9 UT and the Vatican Observatory VATT 1.8-m telescope on Mt. Graham, Arizona on 1999 November 11 and 12 UT. All images were obtained through B, V, and R glass filters on photometric nights.
We find 1999 TD10 exhibits large variations in brightness. It has a lightcurve with an average V magnitude of 20.20, an amplitude of 0.68 magnitudes, which can be fit with a period of 5.8 hr. We find an absolute magnitude, H, of 9.07. If we assume an albedo of 0.04, then 1999 TD10 has a mean diameter of 100 km. If the variation in brightness is due to the rotation of an object with an irregular shape, then the ratio of a/b is 1.88, giving the object dimensions of 130 x 70 km. Such an irregular shape for such a large object would be unusual for a main belt asteroid; however, the largest Trojan, 624 Hektor, may be larger and even more irregular in shape, and the largest irregular moon (Hyperion) has a similar a/b with much larger dimensions (410 x 260 x 220 km).
We find a B-V color of 0.77 +/- 0.02 and a V-R color of 0.47 +/- 0.01. Such colors place 1999 TD10 in the "gray" population of centaurs and KBOs, comparable to the Trojans.