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B. E. Cobb (Williams College), B. J. Buratti, M. D. Hicks (Jet Propulsion Lab), M. Garske (Northwest Nazarene University), J. Ward (Colgate College)
Photometric observations of Triton in the BVRI and 890 nm methane filters were obtained at Table Mountain Observatory during a 7-day observing run in July 2000. The observations span a full rotational period, and they cover the solar phase angles of 0.20 to 0.008 degrees. Disk integrated photometry was performed on the images with IRAF and a false aperture technique to accurately model the scattered light from Neptune. The amplitudes of Triton's lightcurve in all filters show a significant increase from previously recorded values (e.g., Hillier et al., J.G.R Suppl 96, 19,211 (1991)), suggesting that volatile transport has occurred on the satellite's surface during the past decade. Triton's lightcurves are distinctly non-sinusoidal and wavelength dependent, with decreasing amplitudes at increasing wavelengths. Triton's leading hemisphere is brighter than its trailing hemisphere, but the darker, trailing face of Triton exhibits a bright surface feature at 270 degrees longitude. Triton's phase coefficient is small at visual wavelengths (0.013 mag/degree in V), but there is a possible trend in our measurements for the magnitude of the opposition surge to increase with increasing wavelength. This result suggests that the surge may be due in part to coherent backscatter.
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