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New Near-Infrared Solar Coronal Observations...(1Mar94) at NSO/Sac Peak (from NSO, NOAO Newsletter No. 37, 1 March 1994) The first ground-based observations of the Si X coronal emission were made using the 40-cm coronagraph, 3-m Littrow spectrograph, and the Michigan Infrared Camera at the Evans Solar Facility. Two previous observations of this line were made from aircraft flying in the path of a total eclipse. The new wavelength measurement of 1430.08 +- 0.01 nm places the emission in the center of a small atmospheric transmission window - a lucky break for observers! More coronal emission wavelength measurements were made; this time for the two "well-known" Fe XIII emission lines. The new wavelengths for these lines are 1074.62 +- 0.01 nm and 1079.78 +- 0.01 nm. Surprisingly these Fe XIII positions have not been updated since the lines were discovered by Lyot in the 1930's. The intensity of the Si X emission is rather faint; the measured intensities range from 1 to 10 millionths of the solar disk center brightness. This is very different from some recent work whichsuggested that the brightness would be 100 millionths! The 1075 nm Fe XIII emission ranged from 15 to 45 millionths of Sun center brightness, while the 1080 nm emission was about 5 millionths. This work will be detailed in a forthcoming paper. Many other solar coronal emission lines are predicted to exist in the 1000 to 2000 nm wavelength regime. Only one spectrum exists (of a small wavelength region) from data taken in 1970, but recent observations suggest that there may be problems with these measurements. What are the exact wavelengths of these near-IR coronal lines? What are the intensities of these lines? Can these emission lines be used to accurately measure the temperature, density, velocities and magnetic fields of the solar corona? These are the questions driving new work behind the coronagraph at NSO/Sac Peak. [Figure not included] Matt Penn, Jeff Kuhn
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