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Published online by Cambridge University Press: 03 August 2017
Infrared images (1.65 μm) of the eclipsed Sim were taken atop Mauna Kea, Hawaii, during the July 11, 1991 total eclipse with an Amber Engineering 128 × 128 InSb array camera. The camera, mounted on a portable solar tracker, had a 3.8-cm, f/2 objective that produced a 4.9° field of view. The primary objective of the experiment was to search for dust or rocky rings around the Sun, previously detected at about 4 R ⊙. High thin clouds, atmospheric dust and aerosols from the June 1991 explosion of Mount Pinatubo in the Philippines, and the overall brightness of the solar corona resulted in a very high infrared background. Despite this, high signal-to-noise radial infrared intensity profiles were obtained of the solar corona from the Moon's limb out to about 10 R ⊙. Preliminary analysis shows some evidence for an enhanced surface brightness between 3 to 4 R ⊙ along the east-west direction, but much fainter than seen in previous solar eclipses. The transition region between the K-corona and the F-corona clearly shows at 2.5 R ⊙, and the surface brightness of the F-corona as a function of radius (from about 2 to 10 R ⊙) can be fit by a simple power law.