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P. A. Yanamandra-Fisher, B. M. Fisher, G. S. Orton, P. D. Parrish (CIT/Jet Propulsion Laboratatory), T. Fuse, T. Fujiyoshi (NAOJ/Subaru Observatory)
Brightness temperature trends observed on Saturn and its main rings at solar elevation angles ranging from 0 to 26 degrees, available from earth, exhibit the expected increase with solar elevation. However, based on observations from NASA/InfraRed Telescope Facility (IRTF) covering two seasons on Saturn, at intermediate solar elevation (16 - 20 degrees) in 1999 all three rings, A, B and C exhibit a local maximum. The variation of the planet's brightness temperature over the same interval demonstrates similar trends at different latitudes. Since the planet and rings form a coupled system, the planet cannot be used for calibration, unlike the situation when the rings are edge-on (1995) and at their maximum opening (2002-2003). Our results are based on the temporal baseline middle-infrared images of Saturn and rings from NASA/InfraRed Telescope Facility (IRTF) since 1995 and recently from Subaru 8.2m telescope during May and June 2005. The current epoch corresponds to a solar elevation angle of 20 degrees and provides us with a second opportunity to observe Saturn and its rings to determine the variation of brightness temperature, but at a higher spatial resolution, almost comparable to Cassini/Composite InfraRed Spectrometer (CIRS). The compilation of previous results of the brightness temperature of Ring B does not have any information in this range of solar elevation angles. Our results are therefore new and will address the thermal asymmetries in the rings and correlation (if any) with the planet's changing temperature field.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.