36th DPS Meeting, 8-12 November 2004
Session 3 Kuiper Belt I: Observations
Oral, Monday, November 8, 2004, 10:30am-12:noon, Clark

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[3.03] The photometric behavior of 20000 Varuna at very small solar phase angles.

M. D. Hicks, B. J. Buratti, D. P. Simonelli (JPL/Caltech)

In the decade since the discovery of 1992 QB1 (Jewitt & Luu 1993), a vast population of asteroids have been detected beyond the orbit of Neptune. The total mass of the Kuiper belt dwarfs main-belt asteroids, with perhaps 70,000 objects with diameters greater than 100 km and semi-major axis a between 30 and 50 AU (Jewitt et al. 1996). Though challenged by our greater understanding of collisional effects and processing (Davis & Farinella 1996, Durda et al. 2001, Stern 2002), we can assumed that Kuiper Belt Objects (KBOs) represent some of the most pristine asteroids in the Solar System.

20000 Varuna (2000 WR106) is one of the largest and brightest KBOs currently known (McMilllan & Larsen 2000). We took advantage of a well placed Dec 2002-Jan 2003 opposition collect 6 nights of R-band data to quantify the disk integrated photometric behavior down to a phase angle of 0.036 degrees at the Palomar 200 and Palomar 60-inch telescopes and facility CCD imaging systems. After lightcurve subtraction, we found a pronounced 0.1 magnitude opposition surge at angles less than 0.5 degrees. A composite phase curve using our and Jewitt & Sheppard (2002) data allows alows us to fit IAU magnitude parameters (Bowell et al. (1989) H,G of 3.19,-0.35 in the Kron R filter. We shall present the results of our Hapke modeling and analysis, which should shed light on the relative importance of coherent-backscattering and shadow-hiding in the opposition surge.

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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.