Infrared Images of the Sun During the July 11, 1991 Solar Eclipse

Abstract

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.