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Mid-Infrared Solar Imaging at the McMath-Pierce...(1Dec92) Solar Facility (from NSO, NOAO Newsletter No. 32, 1 December 1992) Dan Gezari (NASA/Goddard), William Livingston and Greg Kopp recently imaged active regions and the quiet Sun at several mid-infrared wavelengths, acquiring the most detailed thermal images to date of the solar photosphere. The all-reflecting, windowless McMath-Pierce Solar Facility was used to feed the infrared signal to a cryogenically- cooled 58 x 62 Si:Ge camera system built by Dan Gezari at NASA/Goddard Space Flight Center. Images of sunspots, surrounding plage, and the solar limb were made at 4.8, 12.4, and 18 um. These are basically thermal maps, the infrared intensity being nearly linearly proportional to temperature at these wavelengths. Thermal structure within sunspot penumbrae and the surrounding plage is evident in several images, although umbrae appear homogeneous on scales greater than the 2 arcsec diffraction limit of the telescope at 12 um. Movies of the quiet Sun show temperature changes of about 2% in spatial patterns that change slowly with time. Limb profiles and off-disk measurements will allow for a quantitative characterization of stray light. Seeing in the mid-infrared may be better than in the visible, but seeing distortions are nevertheless present. The infrared capabilities of the McMath-Pierce Solar Facility are promising, this being the first attempt at using it for direct imaging in the thermal infrared. Greg Kopp
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