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J. L. Margot, C. Trujillo, M. E. Brown (California Institute of Technology), F. Bertoldi (Max-Planck-Institut für Radioastronomie)
The discovery of the Kuiper belt object 2002 AW197 by Trujillo and Brown in January 2002 was announced in MPEC 2002-O30. We measured the diameter and albedo of this object by combining measurements of its reflected light and thermal emission. Photometric observations were performed at the Palomar 60-inch telescope and showed that the object has no detectable lightcurve (Trujillo and Brown, in prep.). Thermal emission observations at 1.2 mm wavelength were made using the Max-Planck Millimeter Bolometer (MAMBO) at the IRAM 30 m telescope on Pico Veleta (Spain). Pointing and ephemeris uncertainties were much less than the 10.6 arcsec beamwidth, and the weather conditions were good with zenith opacities less than ~0.2. Average sensitivity was 30 mJy s1/2, and the KBO was clearly detected with a statistical significance of ~4 sigmas.
Our estimate for the diameter of the KBO is 886+115-131 km, which makes it slightly smaller than the largest main-belt asteroid 1 Ceres (~950 km). The red geometric albedo is estimated to be 0.101+0.038-0.022, more than twice the 4% value traditionally assumed for KBOs. Kuiper belt objects may display a wide variety of albedos, as their surfaces likely endure a combination of processes including radiation mantling and impact resurfacing.
The values reported for 20000 Varuna are a diameter of 900+129-145 km and an albedo of 0.070+0.030-0.017 . We note that both objects have relatively high inclinations (~ 20 degrees). Trujillo and Brown  reported a correlation between the inclination and color in the classical Kuiper belt, which possibly emphasizes the role of collisions in altering KBO surfaces.
 Jewitt, Aussel and Evans, Nature, 411, 2001.  Trujillo and Brown, ApJ Letters, 566, 2002.
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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.