Saturn's Rings: Azimuthal variations,phase curves,and radial profiles in four colors |
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| Authors: | WT Thompson K Lumme WM Irvine WA Baum LW Esposito |
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| Institution: | Department of Physics and Astronomy, University of Massachusetts, Amherst, Massachusetts 01003, USA;Onsala Space Observatory, Chalmers University of Technology, S-439 00 Onsala, Sweden;Planetary Research Center, Lowell Observatory, Flagstaff, Arizona 85721, USA;LASP, University of Colorado, Boulder, Colorado 80302, USA |
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| Abstract: | Four-color photographic photometry of Saturn for the 1977–1979 apparitions has been analyzed to determine the dependence of ring brightness on wavelength, solar phase angle, ring particle orbital phase angle (azimuthal effect), declination of the Earth relative to the ring plane (tilt angle), and radial distance from Saturn. Azimuthal brightness variations up to ±20% relative to the ansae are clearly apparent for the maximum of ring A, but are not detectable for ring B or the outer portion of ring A. The shape of the intensity (I) versus orbital phase angle (θ) curve varies with ring tilt (B) and probably with wavelength, and shows 180° symmetry. As characterized by its slope near the ansae, this curve suggests that the azimuthal effect increases as B decreases from 26 to ≈11°. The phase curves l(α) for the ansae show very little dependence on ring tilt (26° > B > 6°), on wavelength, or on radial distance from Saturn; possibly the curves are somewhat steeper at the smallest tilt angles and for ring A relative to ring B. The radial profile of both rings becomes flatter with decreasing tilt angle and with decreasing wavelength. The latter effect is a natural result of the classical, many-particle-thick ring model. |
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