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Y.R. Fernandez (UH-IfA), P.A. Abell (RPI), P. Pravec (Astronomical Inst. ASCR), L.M. French (IWU), T.L. Farnham (UMd), M.J. Gaffey (UND), P.S. Hardersen (UND,RPI), P. Kusnirak, L. Sarounova (Astronomial Inst. ASCR), S.S. Sheppard (UH-IfA)
We present the results from multiwavelength observations of the nucleus of the unusual Comet LONEOS C/2001 OG108. Discovered in July 2001, the object is in a Halley-Family orbit, but was apparently inactive until January 2002, when it was only about 1.5 AU from the Sun and just 2 to 3 months before perihelion. We observed the object in visible, near-IR, and mid-IR wavelengths near its opposition in October and November 2001, while it was still asteroidal. Thus our observations, originally intended to characterize the surface and physical properties of an unusual asteroid, were, in fact, fortuitously of a bare cometary nucleus; perhaps this nucleus is undergoing its last epoch of activity before dormancy. Very few nuclei have been studied in such detail, and even fewer nuclei that belong to comets originating in the Oort Cloud.
We have constrained the nucleus's size, shape, color, reflectance spectrum, albedo, and rotation period. The (near-IR) spectrum, (visible) colors, and geometric albedo most closely resemble those of a D-type asteroid. There are no absorption bands in the 0.75 to 2.4 \mum range at a few percent level, though the spectrum does show a kink near 0.75 \mum. The V-band geometric albedo of the nucleus is 0.030±0.005, and this is well within the currently-known distribution of albedos for other active comets and extinct-comet candidates. Visible-wavelength light curves reveal a double-peaked periodicity of 57.2±0.5 hours with a peak-to-valley range of about 0.3 mag. A measurement of the 10- and 18-\mum flux from the nucleus, combined with the known rotational context, yields an estimate of an ellipsoidal (a > b = c) shape with radii a = 10.1 km and b = 7.9 km. C/2001 OG108's nucleus is both one of the largest known and one of the most slowly rotating.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.